Effects of high-protein diets on fat-free mass and muscle protein synthesis following weight loss: a randomized controlled trial

Common questions and misconceptions about protein supplementation: what does the scientific evidence really show?

Protein supplementation often refers to increasing the intake of this particular macronutrient through dietary supplements in the form of powders, ready-to-drink shakes, and bars. The primary purpose of protein supplementation is to augment dietary protein intake, aiding individuals in meeting their protein requirements, especially when it may be challenging to do so through regular food (i.e. chicken, beef, fish, pork, etc.) sources alone. A large body of evidence shows that protein has an important role in exercising and sedentary individuals. A PubMed search of "protein and exercise performance" reveals thousands of publications. Despite the considerable volume of evidence, it is somewhat surprising that several persistent questions and misconceptions about protein exist. The following are addressed: 1) Is protein harmful to your kidneys? 2) Does consuming "excess" protein increase fat mass? 3) Can dietary protein have a harmful effect on bone health? 4) Can vegans and vegetarians consume enough protein to support training adaptations? 5) Is cheese or peanut butter a good protein source? 6) Does consuming meat (i.e., animal protein) cause unfavorable health outcomes? 7) Do you need protein if you are not physically active? 8) Do you need to consume protein ≤ 1 hour following resistance training sessions to create an anabolic environment in skeletal muscle? 9) Do endurance athletes need additional protein? 10) Does one need protein supplements to meet the daily requirements of exercise-trained individuals? 11) Is there a limit to how much protein one can consume in a single meal? To address these questions, we have conducted a thorough scientific assessment of the literature concerning protein supplementation.

A comprehensive approach to lifestyle intervention based on a calorie-restricted diet ameliorates liver fat in overweight/obese patients with NAFLD: a multicenter randomized controlled trial in China

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is a globally increasing health epidemic. Lifestyle intervention is recommended as the main therapy for NAFLD. However, the optimal approach is still unclear. This study aimed to evaluate the effects of a comprehensive approach of intensive lifestyle intervention (ILI) concerning enhanced control of calorie-restricted diet (CRD), exercise, and personalized nutrition counseling on liver steatosis and extrahepatic metabolic status in Chinese overweight and obese patients with NAFLD.

METHODS

This study was a multicenter randomized controlled trial (RCT) conducted across seven hospitals in China. It involved 226 participants with a body mass index (BMI) above 25. These participants were randomly assigned to two groups: the ILI group, which followed a low carbohydrate, high protein CRD combined with exercise and intensive counseling from a dietitian, and a control group, which adhered to a balanced CRD along with exercise and standard counseling. The main measure of the study was the change in the fat attenuation parameter (FAP) from the start of the study to week 12, analyzed within the per-protocol set. Secondary measures included changes in BMI, liver stiffness measurement (LSM), and the improvement of various metabolic indexes. Additionally, predetermined subgroup analyses of the FAP were conducted based on variables like gender, age, BMI, ethnicity, hyperlipidemia, and hypertension.

RESULTS

A total of 167 participants completed the whole study. Compared to the control group, ILI participants achieved a significant reduction in FAP (LS mean difference, 16.07 [95% CI: 8.90-23.25] dB/m) and BMI (LS mean difference, 1.46 [95% CI: 1.09-1.82] kg/m2) but not in LSM improvement (LS mean difference, 0.20 [95% CI: -0.19-0.59] kPa). The ILI also substantially improved other secondary outcomes (including ALT, AST, GGT, body fat mass, muscle mass and skeletal muscle mass, triglyceride, fasting blood glucose, fasting insulin, HbA1c, HOMA-IR, HOMA-β, blood pressure, and homocysteine). Further subgroup analyses showed that ILI, rather than control intervention, led to more significant FAP reduction, especially in patients with concurrent hypertension (p < 0.001).

CONCLUSION

In this RCT, a 12-week intensive lifestyle intervention program led to significant improvements in liver steatosis and other metabolic indicators in overweight and obese Chinese patients suffering from nonalcoholic fatty liver disease. Further research is required to confirm the long-term advantages and practicality of this approach.

TRIAL REGISTRATION

This clinical trial was registered on ClinicalTrials.gov (registration number: NCT03972631) in June 2019.

Effects of protein-enriched nutritional support on skeletal muscle mass and rehabilitative outcomes in brain tumor patients: a randomized controlled trial

Patients with brain tumors require extensive and prolonged rehabilitation efforts as they suffer from lesion-induced motor weakness as well as treatment-related side effects, often leading to a significant decline in function. Protein supplements have shown positive effects on promoting muscle strength and physical performance in various tumor etiologies. However, reports on their effects specifically in brain tumor patients remain scarce. This study aims to investigate the feasibility and efficacy of protein supplements in enhancing rehabilitative outcomes via muscle strengthening and functional gain in brain tumor patients with neurological demise. Sixty brain tumor patients were randomly assigned to either a protein supplement or a control group, receiving either protein supplements or a placebo for 6 weeks, in conjunction with conventional rehabilitation therapy. Assessments before and after the intervention included laboratory tests, anthropometric measures using bioimpedance analysis, and functional assessments, which included the MMSE, the modified Barthel Index, the Beck Depression Inventory, the Brief Fatigue Inventory, the Timed Up and Go test, the 6-min walk test, the isokinetic quadriceps muscle strength test, and the handgrip power. After the intervention, the levels of serum hemoglobin, protein, albumin, and C-reactive protein were improved in both groups, however, the change was significant only in the protein group. The muscle strength was enhanced in both groups, however, the significant increase in pinch grasp power was only noted in the protein group (P < 0.05). The distance on 6MWT was also significantly extended at follow-up in the protein group (P < 0.01). In the subgroup analysis according to nutritional status, the moderate malnutrition group showed greater augmentation of muscle mass than those with adequate nutrition (P < 0.05). Interestingly, the amelioration of malnutrition was observed only the in protein group. This study using protein supplements to promote the rehabilitative potential of brain tumor patients revealed a significant effect on improving hemodynamic nutritional indices, muscle power reimbursement, and functional improvement, especially in malnourished patients. The safety and feasibility of protein supplements in brain tumor patients were affirmative in this study. Further studies with more patients may help confirm the secondary functional gain resulting from increased muscle power.Trial registration: This study was retrospectively registered in the Clinical Research Information Service, CRIS no. KCT0009113 on Jan 12, 2024.

Fasting mimicking diet in diabetic mice partially preserves glomerular endothelial glycocalyx coverage, without changing the diabetic metabolic environment

Intermittent fasting has become of interest for its possible metabolic benefits and reduction of inflammation and oxidative damage, all of which play a role in the pathophysiology of diabetic nephropathy. We tested in a streptozotocin (60 mg/kg)-induced diabetic apolipoprotein E knockout mouse model whether repeated fasting mimicking diet (FMD) prevents glomerular damage. Diabetic mice received 5 FMD cycles in 10 wk, and during cycles 1 and 5 caloric measurements were performed. After 10 wk, glomerular endothelial morphology was determined together with albuminuria, urinary heparanase-1 activity, and spatial mass spectrometry imaging to identify specific glomerular metabolic dysregulation. During FMD cycles, blood glucose levels dropped while a temporal metabolic switch was observed to increase fatty acid oxidation. Overall body weight at the end of the study was reduced together with albuminuria, although urine production was dramatically increased without affecting urinary heparanase-1 activity. Weight loss was found to be due to lean mass and water, not fat mass. Although capillary loop morphology and endothelial glycocalyx heparan sulfate contents were preserved, hyaluronan surface expression was reduced together with the presence of UDP-glucuronic acid. Mass spectrometry imaging further revealed reduced protein catabolic breakdown products and increased oxidative stress, not different from diabetic mice. In conclusion, although FMD preserves partially glomerular endothelial glycocalyx, loss of lean mass and increased glomerular oxidative stress argue whether such diet regimes are safe in patients with diabetes.NEW & NOTEWORTHY Repeated fasting mimicking diet (FMD) partially prevents glomerular damage in a diabetic mouse model; however, although endothelial glycocalyx heparan sulfate contents were preserved, hyaluronan surface expression was reduced in the presence of UDP-glucuronic acid. The weight loss observed was of lean mass, not fat mass, and increased glomerular oxidative stress argue whether such a diet is safe in patients with diabetes.

Nutritional approaches targeting mitochondria for the prevention of sarcopenia

A decline in function and loss of mass, a condition known as sarcopenia, is observed in the skeletal muscles with aging. Sarcopenia has a negative effect on the quality of life of elderly. Individuals with sarcopenia are at particular risk for adverse outcomes, such as reduced mobility, fall-related injuries, and type 2 diabetes mellitus. Although the pathogenesis of sarcopenia is multifaceted, mitochondrial dysfunction is regarded as a major contributor for muscle aging. Hence, the development of preventive and therapeutic strategies to improve mitochondrial function during aging is imperative for sarcopenia treatment. However, effective and specific drugs that can be used for the treatment are not yet approved. Instead studies on the relationship between food intake and muscle aging have suggested that nutritional intake or dietary control could be an alternative approach for the amelioration of muscle aging. This narrative review approaches various nutritional components and diets as a treatment for sarcopenia by modulating mitochondrial homeostasis and improving mitochondria. Age-related changes in mitochondrial function and the molecular mechanisms that help improve mitochondrial homeostasis are discussed, and the nutritional components and diet that modulate these molecular mechanisms are addressed.

Sex differences in energy balance, body composition, and metabolic and endocrine markers during prolonged arduous military training

This study investigated sex differences in energy balance, body composition, and metabolic and endocrine markers during prolonged military training. Twenty-three trainees (14 women) completed 44-wk military training (three terms of 14 wk with 2-wk adventurous training). Dietary intake and total energy expenditure were measured over 10 days during each term by weighed food and doubly labeled water. Body composition was measured by dual-energy X-ray absorptiometry (DXA) at baseline and at the end of each term. Circulating metabolic and endocrine markers were measured at baseline and at the end of terms 2 and 3. Absolute energy intake and total energy expenditure were higher, and energy balance was lower, for men than women (P ≤ 0.008). Absolute energy intake and balance were lower, and total energy expenditure was higher, during term 2 than terms 1 and 3 (P < 0.001). Lean mass did not change with training (P = 0.081). Fat mass and body fat increased from term 1 to terms 2 and 3 (P ≤ 0.045). Leptin increased from baseline to terms 2 and 3 in women (P ≤ 0.002) but not in men (P ≥ 0.251). Testosterone and free androgen index increased from baseline to term 3 (P ≤ 0.018). Free thyroxine (T4) decreased and thyroid-stimulating hormone (TSH) increased from baseline to term 2 and term 3 (P ≤ 0.031). Cortisol decreased from baseline to term 3 (P = 0.030). IGF-I and total triiodothyronine (T3) did not change with training (P ≥ 0.148). Men experienced greater energy deficits than women during military training due to higher total energy expenditure.NEW & NOTEWORTHY Energy deficits are common in military training and can result in endocrine and metabolic disturbances. This study provides first investigation of sex differences in energy balance, body composition, and endocrine and metabolic markers in response to prolonged and arduous military training. Men experienced greater energy deficits than women due to higher energy expenditure, which was not compensated for by increased energy intake. These energy deficits were not associated with decreases in fat or lean mass or metabolic or endocrine function.

The Importance of Dietary Protein Quality in Mid- to High-Income Countries

In wealthy countries, the protein intake of adults is usually considered to be adequate, and considerations of protein quality are often deemed irrelevant. The objective was to examine dietary protein intakes of adults in developed countries in the context of dietary protein quality. An analysis of NHANES population data on actual protein intakes in the United States (a developed country) demonstrated that for a dietary Digestible Indispensable Amino Acid Score (DIAAS) of 100%, 11% of the adult (19-50 y) population had habitual protein intakes below the Estimated Average Requirement (EAR) and 22% below the Recommended Dietary Allowance. The percentage of the population with utilizable protein intakes potentially falling below the EAR increased as the assumed DIAAS declined. Analysis of the NHANES data and several other datasets also indicated that total protein intakes can be limiting or close to limiting for the elderly and some vegetarians and vegans. Here, lower dietary protein quality can potentially lead to inadequate utilizable protein intakes. For many people in specific physiological states (e.g., weight loss, endurance sports, resistance exercise) attempting to meet higher dietary protein targets often with accompanying lowered energy intakes, low dietary protein quality can lead to protein calories expressed as a proportion of total calories, falling outside what may be acceptable limits (maximum of 30% protein calories from total calories). In general, individuals within the adult population may be susceptible to macronutrient imbalance (whenever total protein intakes are high, daily energy intakes low) and for diets with lower protein quality (DIAAS <100%). Our analysis shows that dietary protein quality is relevant in mid- to high-income countries.

High-protein diet with immediate post-exercise protein drink: Impact on appetite in middle-aged obesity

Successful management of obesity can be challenging if individuals constantly experience cravings. The present study investigated the effects of a high-protein diet, including a high-protein drink consumed immediately after high-intensity interval training (HIIT), on appetite and weight loss in obese middle-aged individuals. A total of 52 obese middle-aged individuals (58.2 ± 4.11 years old) were randomly assigned to one of three groups: the exercise group (E, n=19), exercise and high-protein diet group (ED, n=21), and a control group (n=12). The E and ED groups engaged in cycling HIIT (comprising 90 % of peak heart rate (HRpeak) for 3 min, followed by 70 % of HRpeak for 3 min, for a total of 5 cycles) three times a week for 3 months. The ED group consumed a high-protein drink immediately after HIIT and had a daily protein intake of 1.6g/kg. Body composition and eating behavior were assessed before and after the intervention. Additionally, appetite levels were measured before and after each exercise session, before dinner, and before bedtime during three phases of the intervention: the first phase (weeks 3-4), the second phase (weeks 5-8), and the third phase (weeks 9-12). Results showed that only the ED group experienced a decrease in body mass index (from 27.4 ± 4.28 to 26.8 ± 4.09 kg/m2, p=0.04). Appetite significantly increased after exercise in both E and ED groups (p values for the three phases ranged from 0.04 to 0.001 for the E group and from 0.042 to 0.003 for the ED group). The desire to eat significantly increased after exercise in the E group (phase 1: p = 0.026; phase 2: p = 0.011; phase 3: p = 0.003), but not in the ED group. Furthermore, the frequency of late-night snacking decreased in the ED group (the score changed from 2.4 ± 0.86 to 2.7 ± 0.80, p = 0.034). Notably, the E group tended to have a higher pre-dinner appetite score than the ED group in the third phase (p = 0.063). In summary, a high daily protein intake, combined with the consumption of high-protein drinks after exercise, resulted in reduced post-exercise appetite and a decrease in the frequency of late-night snacking.

Impact of EASO/ESPEN-Defined Sarcopenic Obesity Following a Technology-Based Weight Loss Intervention

BACKGROUND

Sarcopenic Obesity is the co-existence of increased adipose tissue (obesity) and decreased muscle mass or strength (sarcopenia) and is associated with worse outcomes than obesity alone. The new EASO/ESPEN consensus provides a framework to standardize its definition. This study sought to evaluate whether there are preliminary differences observed in weight loss or physical function in older adults with and without sarcopenic obesity taking part in a multicomponent weight loss intervention using these new definitions.

METHODS

A 6-month, non-randomized, non-blinded, single-arm pilot study was conducted from 2018 to 2020 in adults ≥ 65 years with a body mass index (BMI) ≥ 30 kg/m2. Weekly dietitian visits and twice-weekly physical therapist-led exercise classes were delivered using telemedicine. We conducted a secondary retrospective analysis of the parent study (n = 53 enrolled, n = 44 completers) that investigated the feasibility of a technology-based weight management intervention in rural older adults with obesity. Herein, we applied five definitions of sarcopenic obesity (outlined in the consensus) to ascertain whether the response to the intervention differed among those with and without sarcopenic obesity. Primary outcomes evaluated included weight loss and physical function (30-s sit-to-stand).

RESULTS

In the parent study, mean weight loss was - 4.6 kg (95% CI - 3.6, - 5.6; p < 0.001). Physical function measures of 30-s sit-to-stand showed a mean increase of 3.1 in sit-to-stand repetitions (+ 1.9, + 4.3; p < 0.001). In this current analysis, there was a significant decrease in weight and an increase in repetitions between baseline and follow-up within each group of individuals with and without sarcopenia for each of the proposed definitions. However, we did not observe any significant differences in the changes between groups from baseline to follow-up.

CONCLUSIONS

The potential lack of significant differences in weight loss or physical function between older adults with and without sarcopenic obesity participating in a weight loss intervention may suggest that well-designed, multicomponent interventions can lead to similar outcomes irrespective of sarcopenia status in persons with obesity. Fully powered randomized clinical trials are critically needed to confirm these preliminary results.

Dose-Response of Myofibrillar Protein Synthesis To Ingested Whey Protein During Energy Restriction in Overweight Postmenopausal Women: A Randomized, Controlled Trial

BACKGROUND

Diet-induced weight loss is associated with a decline in lean body mass, as mediated by an impaired response of muscle protein synthesis (MPS). The dose-response of MPS to ingested protein, with or without resistance exercise, is well characterized during energy balance but limited data exist under conditions of energy restriction in clinical populations.

OBJECTIVE

To determine the dose-response of MPS to ingested whey protein following short-term diet-induced energy restriction in overweight, postmenopausal, women at rest and postexercise.

DESIGN

Forty middle-aged (58.6±0.4 y), overweight (BMI: 28.6±0.4), postmenopausal women were randomly assigned to 1 of 4 groups: Three groups underwent 5 d of energy restriction (∼800 kcal/d). On day 6, participants performed a unilateral leg resistance exercise bout before ingesting either a bolus of 15g (ERW15, n = 10), 35g (ERW35, n = 10) or 60g (ERW60, n = 10) of whey protein. The fourth group (n = 10) ingested a 35g whey protein bolus after 5 d of an energy balanced diet (EBW35, n = 10). Myofibrillar fractional synthetic rate (FSR) was calculated under basal, fed (FED) and postexercise (FED-EX) conditions by combining an L-[ring-13C6] phenylalanine tracer infusion with the collection of bilateral muscle biopsies.

RESULTS

Myofibrillar FSR was greater in ERW35 (0.043±0.003%/h, P = 0.013) and ERW60 (0.042±0.003%/h, P = 0.026) than ERW15 (0.032 ± 0.003%/h), with no differences between ERW35 and ERW60 (P = 1.000). Myofibrillar FSR was greater in FED (0.044 ± 0.003%/h, P < 0.001) and FED-EX (0.048 ± 0.003%/h, P < 0.001) than BASAL (0.027 ± 0.003%/h), but no differences were detected between FED and FED-EX (P = 0.732) conditions. No differences in myofibrillar FSR were observed between EBW35 (0.042 ± 0.003%/h) and ERW35 (0.043 ± 0.003%/h, P = 0.744).

CONCLUSION

A 35 g dose of whey protein, ingested with or without resistance exercise, is sufficient to stimulate a maximal acute response of MPS following short-term energy restriction in overweight, postmenopausal women, and thus may provide a per serving protein recommendation to mitigate muscle loss during a weight loss program.

TRIAL REGISTRY

clinicaltrials.gov (ID: NCT03326284).

A Nutrigenetic Strategy for Reducing Blood Lipids and Low-Grade Inflammation in Adults with Obesity and Overweight

The pathogenesis of obesity and dyslipidemia involves genetic factors, such as polymorphisms related to lipid metabolism alterations predisposing their development. This study aimed to evaluate the effect of a nutrigenetic intervention on the blood lipid levels, body composition, and inflammation markers of adults with obesity and overweight. Eleven genetic variants associated with dyslipidemias in Mexicans were selected, and specific nutrigenetic recommendations for these polymorphisms were found. One hundred and one adults were recruited and assigned to follow either a standard or nutrigenetic diet for eight weeks. Anthropometric, biochemical, body composition, and inflammation markers were evaluated through standardized methods. Weighted genetic risk scores (wGRSs) were computed using the study polymorphisms. After intervention, both diets significantly decreased the anthropometric parameters and body composition (p < 0.05). Only the nutrigenetic diet group showed significant reductions in VLDL-c (p = 0.001), triglycerides (p = 0.002), TG:HDL (p = 0.002), IL-6 (p = 0.002), and TNF-α (p = 0.04). wGRSs had a high impact on the ΔTGs and ΔVLDL-c of both groups (standard diet: ΔTGs: Adj R2 = 0.69, p = 0.03; ΔVLDL-c: Adj R2 = 0.71, p = 0.02; nutrigenetic diet: ΔTGs: Adj R2 = 0.49, p = 0.03 and ΔVLDL-c: R2 = 0.29, p = 0.04). This nutrigenetic intervention improved lipid abnormalities in patients with excessive body weight. Hence, nutrigenetic strategies could be coadjuvant tools and enhance the standard dietary treatment for cardiometabolic diseases.

Post-Exercise Protein Intake May Reduce Time in Hypoglycemia Following Moderate-Intensity Continuous Exercise among Adults with Type 1 Diabetes

Little is known about the role of post-exercise protein intake on post-exercise glycemia. Secondary analyses were conducted to evaluate the role of post-exercise protein intake on post-exercise glycemia using data from an exercise pilot study. Adults with T1D (n = 11), with an average age of 33.0 ± 11.4 years and BMI of 25.1 ± 3.4, participated in isoenergetic sessions of high-intensity interval training (HIIT) or moderate-intensity continuous training (MICT). Participants completed food records on the days of exercise and provided continuous glucose monitoring data throughout the study, from which time in range (TIR, 70-180 mg/dL), time above range (TAR, >180 mg/dL), and time below range (TBR, <70 mg/dL) were calculated from exercise cessation until the following morning. Mixed effects regression models, adjusted for carbohydrate intake, diabetes duration, and lean mass, assessed the relationship between post-exercise protein intake on TIR, TAR, and TBR following exercise. No association was observed between protein intake and TIR, TAR, or TBR (p-values ≥ 0.07); however, a borderline significant reduction of -1.9% (95% CI: -3.9%, 0.0%; p = 0.05) TBR per 20 g protein was observed following MICT in analyses stratified by exercise mode. Increasing post-exercise protein intake may be a promising strategy to mitigate the risk of hypoglycemia following MICT.

Diet, Supplementation and Nutritional Habits of Climbers in High Mountain Conditions

Appropriate nutritional preparation for a high-mountain expedition can contribute to the prevention of nutritional deficiencies affecting the deterioration of health and performance. The aim of the study was to analyze the dietary habits, supplementation and nutritional value of diets of high mountain climbers. The study group consisted of 28 men (average age 33.12 ± 5.96 years), taking part in summer mountaineering expeditions at an altitude above 3000 m above sea level, lasting at least 3 weeks. Food groups consumed with low frequency during the expedition include vegetables, fruits, eggs, milk and milk products, butter and cream, fish and meat. The energy demand of the study participants was 4559.5 ± 425 kcal, and the energy supply was 2776.8 ± 878 kcal. The participants provided 79.6 ± 18.5 g of protein (1.1 ± 0.3 g protein/kg bw), 374.0 ± 164.5 g of carbohydrates (5.3 ± 2.5 g/kg bw) and 110.7 ± 31.7 g of fat (1.6 ± 0.5 g/kg bw) in the diet. The climbers' diet was low in calories, the protein supply was too low, and the fat supply was too high. There is a need to develop nutritional and supplementation recommendations that would serve as guidelines for climbers, improving their well-being and exercise capacity in severe high-mountain conditions, which would take their individual taste preferences into account.

The Role of Dietary Protein in Body Weight Regulation among Active-Duty Military Personnel during Energy Deficit: A Systematic Review

Active-duty military personnel are subjected to sustained periods of energy deficit during combat and training, leaving them susceptible to detrimental reductions in body weight. The importance of adequate dietary protein intake during periods of intense physical training is well established, where previous research has primarily focused on muscle protein synthesis, muscle recovery, and physical performance. Research on how protein intake may influence body weight regulation in this population is lacking; therefore, the objective of this review was to evaluate the role of dietary protein in body weight regulation among active-duty military during an energy deficit. A literature search based on fixed inclusion and exclusion criteria was performed. English language peer-reviewed journal articles from inception to 3 June 2023 were selected for extraction and quality assessment. Eight studies were identified with outcomes described narratively. The study duration ranged from eight days to six months. Protein was directly provided to participants in all studies except for one. Three studies supplied additional protein via supplementation. The Downs and Black Checklist was used to assess study quality. Five studies were classified as good, two as fair, and one as excellent. All studies reported mean weight loss following energy deficit: the most severe was 4.0 kg. Protein dose during energy deficit varied from 0.5 g/kg/day to 2.4 g/kg/day. Six studies reported mean reductions in fat mass, with the largest being 4.5 kg. Four studies reported mean reductions in fat-free mass, while two studies reported an increase. Results support the recommendation that greater than 0.8 g/kg/day is necessary to mitigate the impact of energy deficit on a decline in lean body mass, while intakes up to 1.6 g/kg/day may be preferred. However, exact recommendations cannot be inferred as the severity and duration of energy deficit varied across studies. Longer and larger investigations are needed to elucidate protein's role during energy deficit in active-duty military.

Low energy availability reduces myofibrillar and sarcoplasmic muscle protein synthesis in trained females

Low energy availability (LEA) describes a state where the energy intake is insufficient to cover the energy costs of both exercise energy expenditure and basal physiological body functions. LEA has been associated with various physiological consequences, such as reproductive dysfunction. However, the effect of LEA on skeletal muscle protein synthesis in females performing exercise training is still poorly understood. We conducted a randomized controlled trial to investigate the impact of LEA on daily integrated myofibrillar and sarcoplasmic muscle protein synthesis in trained females. Thirty eumenorrheic females were matched based on training history and randomized to undergo 10 days of LEA (25 kcal · kg fat-free mass (FFM)-1  · day-1 ) or optimal energy availability (OEA, 50 kcal · kg FFM-1  · day-1 ). Before the intervention, both groups underwent a 5-day 'run-in' period with OEA. All foods were provided throughout the experimental period with a protein content of 2.2 g kg lean mass-1  · day-1 . A standardized, supervised combined resistance and cardiovascular exercise training programme was performed over the experimental period. Daily integrated muscle protein synthesis was measured by deuterium oxide (D2 O) consumption along with changes in body composition, resting metabolic rate, blood biomarkers and 24 h nitrogen balance. We found that LEA reduced daily integrated myofibrillar and sarcoplasmic muscle protein synthesis compared with OEA. Concomitant reductions were observed in lean mass, urinary nitrogen balance, free androgen index, thyroid hormone concentrations and resting metabolic rate following LEA. These results highlight that LEA may negatively affect skeletal muscle adaptations in females performing exercise training. KEY POINTS: Low energy availability (LEA) with potential health and performance impairments is widespread among female athletes. We investigated the impact of 10 days of LEA on daily integrated myofibrillar and sarcoplasmic muscle protein synthesis in young, trained females. We show that LEA impairs myofibrillar and sarcoplasmic muscle protein synthesis in trained females performing exercise training. These findings suggest that LEA may have negative consequences for skeletal muscle adaptations and highlight the importance of ensuring adequate energy availability in female athletes.

Association of Macronutrients Intake with Body Composition and Sarcopenic Obesity in Children and Adolescents: A Population-Based Analysis of the National Health and Nutrition Examination Survey (NHANES) 2011-2018

The association of macronutrients intake with body composition and sarcopenic obesity remains uncertain in children and adolescents. We aimed to explore the association between macronutrients intake and body composition, especially sarcopenic obesity, in children and adolescents residing in the United States. The study utilized data from 5412 participants aged 6-17 years who attended NHANES between 2011 and 2018. Body composition was assessed using DXA, and nutrient intake was based on 24-h recall. Multivariable linear regression and multinomial logistic regression were used. The unweighted prevalence of sarcopenic obesity was 15.6%. A higher percentage of energy (5 %E) from fat was inversely associated with muscle mass but positively associated with fat mass and sarcopenic obesity. Substituting carbohydrate (5 %E) with fat decreased muscle mass by 0.03 (95% CI 0.01 to 0.06) but increased fat mass by 0.03 (95% CI 0.01 to 0.06) and increased the prevalence of sarcopenic obesity by 254% (95% CI 15% to 487%). Replacing protein intake with fat intake also increased the OR of sarcopenic obesity (OR, 2.36 [95% CI 1.18 to 3.18]). In conclusion, a high-fat diet, coupled with low carbohydrate/protein intake, is associated with sarcopenic obesity among children and adolescents. The change in children's diet towards a healthy diet with low fat composition may help prevent sarcopenic obesity. However, randomized clinical trials or longitudinal studies are needed to further validate our findings.

Metabolic Adaptations and Substrate Oxidation are Unaffected by Exogenous Testosterone Administration during Energy Deficit in Men

INTRODUCTION/PURPOSE

The effects of testosterone on energy and substrate metabolism during energy deficit are unknown. The objective of this study was to determine the effects of weekly testosterone enanthate (TEST; 200 mg·wk -1 ) injections on energy expenditure, energy substrate oxidation, and related gene expression during 28 d of energy deficit compared with placebo (PLA).

METHODS

After a 14-d energy balance phase, healthy men were randomly assigned to TEST ( n = 24) or PLA ( n = 26) for a 28-d controlled diet- and exercise-induced energy deficit (55% below total energy needs by reducing energy intake and increasing physical activity). Whole-room indirect calorimetry and 24-h urine collections were used to measure energy expenditure and energy substrate oxidation during balance and deficit. Transcriptional regulation of energy and substrate metabolism was assessed using quantitative reverse transcription-polymerase chain reaction from rested/fasted muscle biopsy samples collected during balance and deficit.

RESULTS

Per protocol design, 24-h energy expenditure increased ( P < 0.05) and energy intake decreased ( P < 0.05) in TEST and PLA during deficit compared with balance. Carbohydrate oxidation decreased ( P < 0.05), whereas protein and fat oxidation increased ( P < 0.05) in TEST and PLA during deficit compared with balance. Change (∆; deficit minus balance) in 24-h energy expenditure was associated with ∆activity factor ( r = 0.595), but not ∆fat-free mass ( r = 0.147). Energy sensing (PRKAB1 and TP53), mitochondria (TFAM and COXIV), fatty acid metabolism (CD36/FAT, FABP, CPT1b, and ACOX1) and storage (FASN), and amino acid metabolism (BCAT2 and BCKHDA) genes were increased ( P < 0.05) during deficit compared with balance, independent of treatment.

CONCLUSIONS

These data demonstrate that increased physical activity and not exogenous testosterone administration is the primary determinate of whole-body and skeletal muscle metabolic adaptations during diet- and exercise-induced energy deficit.

Ketogenic Diet Applied in Weight Reduction of Overweight and Obese Individuals with Progress Prediction by Use of the Modified Wishnofsky Equation

Ketogenic diet is often used as diet therapy for certain diseases, among other things, its positive effect related to weight loss is highlighted. Precisely because of the suggestion that KD can help with weight loss, visceral obesity, and appetite control, 100 respondents joined the weight loss program (of which 31% were men and 69% were women). The aforementioned respondents were interviewed in order to determine their eating habits, the amount of food consumed, and the time when they consume meals. Basic anthropometric data (body height, body mass, chest, waist, hips, biceps, and thigh circumferences) were also collected, in order to be able to monitor their progress during the different phases of the ketogenic diet. Important information is the expected body mass during the time frame of a certain keto diet phase. This information is important for the nutritionist, medical doctor, as well as for the participant in the reduced diet program; therefore, the model was developed that modified the original equation according to Wishnofsky. The results show that women lost an average of 22.7 kg (average number of days in the program 79.5), and for men the average weight loss was slightly higher, 29.7 kg (with an average of 76.8 days in the program). The prediction of expected body mass by the modified Wishnofsky's equation was extremely well aligned with the experimental values, as shown by the Bland-Altman graph (bias for women 0.021 kg and -0.697 kg for men) and the coefficient of determination of 0.9903. The modification of the Wishnofsky equation further shed light on the importance of controlled energy reduction during the dietetic options of the ketogenic diet.

Effect of increased protein intake and exogenous ketosis on body composition, energy expenditure and exercise capacity during a hypocaloric diet in recreational female athletes

Introduction: Since low body weight is an important determinant of success in many sports such as gymnastics, martial arts and figure skating, athletes can benefit from effective weight loss strategies that preserve muscle mass and athletic performance. The present study investigates the effects of increased protein intake and exogenous ketosis on body composition, energy expenditure, exercise capacity, and perceptions of appetite and well-being during a hypocaloric diet in females. Methods: Thirty-two female recreational athletes (age: 22.2 ± .5 years; body weight: 58.3 ± .8 kg; BMI: 20.8 ± .2 kg·m^-2) underwent 4 weeks of 30% caloric restriction and were randomized to receive either an increased daily amount of dietary protein (PROT, ∼2.0-2.2 g protein·kg^-1·day^-1), 3 × 20 g·day^-1 of a ketone ester (KE), or an isocaloric placebo (PLA). Body composition was measured by DXA, resting energy expenditure (REE) by indirect calorimetry, exercise capacity during a VO₂max test, appetite hormones were measured in serum, and perceptions of general well-being were evaluated via questionnaires. Results: The hypocaloric diet reduced body weight by 3.8 ± .3 kg in PLA, 3.2 ± .3 kg in KE and 2.4 ± .2 kg in PROT (P_time<.0001). The drop in fat mass was similar between treatments (average: 2.6 ± .1 kg, P_time<.0001), while muscle mass was only reduced in PLA and KE (average: .8 ± .2 kg, P_time<.05), and remained preserved in PROT (P_interaction<.01). REE [adjusted for lean mass] was reduced after caloric restriction in PLA (pre: 32.7 ± .5, post: 28.5 ± .6 kcal·day^-1·kg^-1) and PROT (pre: 32.9 ± 1.0, post: 28.4 ± 1.0 kcal·day^-1·kg^-1), but not in KE (pre: 31.8 ± .9, post: 30.4 ± .8 kcal·day^-1·kg^-1) (P_interaction<.005). Furthermore, time to exhaustion during the VO₂max test decreased in PLA (by 2.5 ± .7%, p < .05) but not in KE and PROT (P_interaction<.05). Lastly, the perception of overall stress increased in PLA and PROT (p < .05), but not in KE (P_interaction<.05). Conclusion: Increased protein intake effectively prevented muscle wasting and maintained exercise capacity during a period of caloric restriction in female recreational athletes. Furthermore, exogenous ketosis did not affect body composition, but showed its potential in weight management by preserving a drop in exercise capacity and REE and by improving overall stress parameters during a period of caloric restriction.

How dietary amino acids and high protein diets influence insulin secretion

Glucose homeostasis is the maintenance and regulation of blood glucose concentration within a tight physiological range, essential for the functioning of most tissues and organs. This is primarily achieved by pancreatic secretion of insulin and glucagon. Deficient pancreatic endocrine function, coupled with or without peripheral insulin resistance leads to prolonged hyperglycemia with chronic impairment of glucose homeostasis, most commonly seen in diabetes mellitus. High protein diets (HPDs) are thought to modulate glucose homeostasis through various metabolic pathways. Insulin secretion can be directly modulated by the amino acid products of protein digestion, which activate nutrient receptors and nutrient transporters expressed by the endocrine pancreas. Insulin secretion can also be modulated indirectly, through incretin release from enteroendocrine cells, and via vagal neuronal pathways. Additionally, glucose homeostasis can be promoted by the satiating effects of anorectic hormones released following HPD consumption. This review summarizes the insulinotropic mechanisms by which amino acids and HPDs may influence glucose homeostasis, with a particular focus on their applicability in the management of Type 2 diabetes mellitus.

Testosterone status following short-term, severe energy deficit is associated with fat-free mass loss in U.S. Marines

The objective of this study was to determine metabolic and physiological differences between males with low testosterone (LT) versus those with normal testosterone (NT) following a period of severe energy deficit. In this secondary analysis, 68 male US Marines (mean ± SD, 24.6 ± 2.4 y) were dichotomized by testosterone concentration (< or ≥ 10.5 nmol/L as determined from a single blood sample collected between 0600-0630 after an 8-10 h overnight fast by automated immunoassay) following 7 days of near complete starvation (~300 kcal consumed/d, ~85% energy deficit) during Survival, Evasion, Resistance, and Escape (SERE) training. Dietary intake was assessed before (PRE) SERE. Body composition (dual-energy x-ray absorptiometry and peripheral quantitative computed tomography) and whole-body protein turnover (15 N alanine) were assessed before (PRE) and after (POST) SERE. Mean testosterone concentrations decreased PRE (17.5 ± 4.7 nmol/L) to POST (9.8 ± 4.0 nmol/L, p < 0.0001). When volunteers were dichotomized by POST testosterone concentrations [NT (n = 24) 14.1 ± 3.4 vs. LT (n = 44): 7.5 ± 1.8 nmol/L, p < 0.0001], PRE BMI, total fat mass, trunk fat mass, and testosterone were greater and the diet quality score and total carbohydrate intake were lower in NT compared to LT (p ≤ 0.05). LT lost more fat-free mass and less fat mass, particularly in the trunk region, compared to NT following SERE (p-interaction≤0.044). Whole-body protein synthesis, net balance, and flux decreased and whole-body protein breakdown increased from PRE to POST in both groups (p-time ≤0.025). Following short-term, severe energy deficit, Marines who exhibited low testosterone had greater fat-free mass loss than those who maintained normal testosterone concentrations. Altering body composition and dietary strategies prior to physical training that elicits severe energy deficit may provide an opportunity to attenuate post-training decrements in testosterone and its associated effects (e.g., loss of lean mass, performance declines, fatigue).

Biomarkers of Frailty: miRNAs as Common Signatures of Impairment in Cognitive and Physical Domains

The past years have seen an increasing concern about frailty, owing to the growing number of elderly people and the major impact of this syndrome on health and social care. The identification of frail people passes through the use of different tests and biomarkers, whose concerted analysis helps to stratify the populations of patients according to their risk profile. However, their efficiency in prognosis and their capability to reflect the multisystemic impairment of frailty is discussed. Recent works propose the use of miRNAs as biological hallmarks of physiological impairment in different organismal districts. Changes in miRNAs expression have been described in biological processes associated with phenotypic outcomes of frailty, opening intriguing possibilities for their use as biomarkers of fragility. Here, with the aim of finding reliable biomarkers of frailty, while considering its complex nature, we revised the current literature on the field, for uncovering miRNAs shared across physical and cognitive frailty domains. By applying in silico analyses, we retrieved the top-ranked shared miRNAs and their targets, finally prioritizing the most significant ones. From this analysis, ten miRNAs emerged which converge into two main biological processes: inflammation and energy homeostasis. Such markers, if validated, may offer promising capabilities for early diagnosis of frailty in the elderly population.

The Health Benefits of Egg Protein

Once the general public accepts that dietary cholesterol is not a concern for cardiovascular disease risk, foods that have been labeled as high-cholesterol sources, including eggs, may be appreciated for their various other dietary components. One of the nutrients in eggs that deserves further discussion is egg protein. Egg protein has been recognized to be highly digestible and an excellent source of essential amino acids, with the highest attainable protein digestibility-corrected amino acid score. Egg protein has been shown to decrease malnutrition in underdeveloped countries, possibly increase height in children, and protect against kwashiorkor. Egg protein has been demonstrated to be important to skeletal muscle health and protective against sarcopenia. Egg protein also can decrease appetite, resulting in a reduction in the caloric intake from the next meal and weight reduction. Other protective effects of egg protein addressed in this review include protection against infection as well as hypotensive and anti-cancer effects.

Effects of Testosterone on Mixed-Muscle Protein Synthesis and Proteome Dynamics During Energy Deficit

CONTEXT

Effects of testosterone on integrated muscle protein metabolism and muscle mass during energy deficit are undetermined.

OBJECTIVE

The objective was to determine the effects of testosterone on mixed-muscle protein synthesis (MPS), proteome-wide fractional synthesis rates (FSR), and skeletal muscle mass during energy deficit.

DESIGN

This was a randomized, double-blind, placebo-controlled trial.

SETTING

The study was conducted at Pennington Biomedical Research Center.

PARTICIPANTS

Fifty healthy men.

INTERVENTION

The study consisted of 14 days of weight maintenance, followed by a 28-day 55% energy deficit with 200 mg testosterone enanthate (TEST, n = 24) or placebo (PLA, n = 26) weekly, and up to 42 days of ad libitum recovery feeding.

MAIN OUTCOME MEASURES

Mixed-MPS and proteome-wide FSR before (Pre), during (Mid), and after (Post) the energy deficit were determined using heavy water (days 1-42) and muscle biopsies. Muscle mass was determined using the D3-creatine dilution method.

RESULTS

Mixed-MPS was lower than Pre at Mid and Post (P < 0.0005), with no difference between TEST and PLA. The proportion of individual proteins with numerically higher FSR in TEST than PLA was significant by 2-tailed binomial test at Post (52/67; P < 0.05), but not Mid (32/67; P > 0.05). Muscle mass was unchanged during energy deficit but was greater in TEST than PLA during recovery (P < 0.05).

CONCLUSIONS

The high proportion of individual proteins with greater FSR in TEST than PLA at Post suggests exogenous testosterone exerted a delayed but broad stimulatory effect on synthesis rates across the muscle proteome during energy deficit, resulting in muscle mass accretion during subsequent recovery.

Circulating and skeletal muscle microRNA profiles are more sensitive to sustained aerobic exercise than energy balance in males

KEY POINTS

Circulating and skeletal muscle miRNA profiles are more sensitive to high levels of aerobic exercise-induced energy expenditures compared to energy status Changes in circulating miRNA in response to high levels of daily sustained aerobic exercise are not reflective of changes in skeletal muscle miRNA.

ABSTRACT

MicroRNA (miRNA) regulate molecular processes governing muscle metabolism. Physical activity and energy balance influence both muscle anabolism and metabolism, but whether circulating and skeletal muscle miRNA mediate those effects remains unknown. This study assessed the impact of sustained physical activity with participants in energy balance (BAL) or deficit (DEF) on circulating and skeletal muscle miRNA. Using a randomized cross-over design, 10 recreational active healthy males (mean ± SD; 22±5 yrs, 87±11 kg) completed 72 hours of high aerobic exercise-induced energy expenditures in BAL (689±852 kcal/d) or DEF (-2047±920 kcal/d). Blood and muscle samples were collected under rested/fasted conditions before (PRE) and immediately after 120-min load carriage exercise bout at the end (POST) of the 72 hours. Trials were separated by 7 days. Circulating and skeletal muscle miRNA were measured using microarray RT-qPCR. Independent of energy status, 36 circulating miRNA decreased (P<0.05), while 10 miRNA increased and 3 miRNA decreased in skeletal muscle (P<0.05) at POST compared to PRE. Of these, miR-122-5p, miR-221-3p, miR-222-3p, and miR-24-3p decreased in circulation and increased in skeletal muscle. Two circulating (miR-145-5p and miR-193a-5p) and 4 skeletal muscle (miR-21-5p, miR-372-3p, miR-34a-5p, and miR-9-5p) miRNA had time-by-treatment effects (P<0.05). These data suggest that changes in miRNA profiles are more sensitive to increased physical activity compared to energy status, and that changes in circulating miRNA in response to high levels of daily aerobic exercise are not reflective of changes in skeletal muscle miRNA. Graphical abstract legend In response to 72 hours of high aerobic exercise, circulating miRNA decreased and miRNA in skeletal muscle primarily increased. The changes in miRNA occurred independent of energy status (i.e., exercise-induced energy defcit or exercise plus increased energy intake to achieve energy balance), and circulating miRNA did not refect changes in skeletal muscle. This article is protected by copyright. All rights reserved.

Higher protein intake during caloric restriction improves diet quality and attenuates loss of lean body mass

OBJECTIVE

Higher protein intake during weight loss is associated with better health outcomes, but whether this is because of improved diet quality is not known. The purpose of this study was to examine how the change in self-selected protein intake during caloric restriction (CR) alters diet quality and lean body mass (LBM).

METHODS

In this analysis of pooled data from multiple weight loss trials, 207 adults with overweight or obesity were examined before and during 6 months of CR (approximately 10 food records/person). Body composition was measured by dual-energy x-ray absorptiometry. Diet quality was assessed using the Healthy Eating Index in 2 groups: lower (LP) and higher (HP) protein intake.

RESULTS

Participants (mean [SD], 54 [11] years; 29 [4] kg/m² ) lost 5.0% (5.4%) of weight. Protein intake was 79 (9) g/d (1.0 [0.2] g/kg/d) and 58 (6) g/d (0.8 [0.1] g/kg/d) in the HP and LP groups, respectively (p < 0.05), and there was an attenuated LBM (kilograms) loss in the HP (-0.6% [1.5%]) compared with the LP (-1.2% [1.4%]) group (p < 0.01). The increased Healthy Eating Index score in the HP compared with the LP group was attributed to greater total protein and green vegetable intake and reduced refined grain and added-sugar intake (p < 0.05).

CONCLUSIONS

Increasing dietary protein during CR improves diet quality and may be another reason for reduced LBM, but it requires further study.

Effects of Intermittent Energy Restriction Alone and in Combination with Sprint Interval Training on Body Composition and Cardiometabolic Biomarkers in Individuals with Overweight and Obesity

The popularity of intermittent fasting (IF) and high intensity (sprint) interval training (SIT) has increased in recent years amongst the general public due to their purported health benefits and feasibility of incorporation into daily life. The number of scientific studies investigating these strategies has also increased, however, very few have examined the combined effects, especially on body composition and cardiometabolic biomarkers, which is the primary aim of this investigation. A total of thirty-four male and female participants (age: 35.4 ± 8.4 y, body mass index (BMI): 31.3 ± 3.5 kg/m2, aerobic capacity (VO2peak) 27.7 ± 7.0 mL·kg−1·min−1) were randomized into one of three 16-week interventions: (1) 5:2 IF (2 non-consecutive days of fasting per week, 5 days on ad libitum eating), (2) supervised SIT (3 bouts per week of 20s cycling at 150% VO2peak followed by 40 s of active rest, total 10 min duration), and (3) a combination of both interventions. Body composition, haemodynamic and VO2peak were measured at 0, 8 and 16 weeks. Blood samples were also taken and analysed for lipid profiles and markers of glucose regulation. Both IF and IF/SIT significantly decreased body weight, fat mass and visceral fat compared to SIT only (p < 0.05), with no significant differences between diet and diet + exercise combined. The effects of diet and/or exercise on cardiometabolic biomarkers were mixed. Only exercise alone or with IF significantly increased cardiorespiratory fitness. The results suggest that energy restriction was the main driver of body composition enhancement, with little effect from the low volume SIT. Conversely, to achieve benefits in cardiorespiratory fitness, exercise is required.

Ketogenic diets, physical activity and body composition: a review

Obesity remains a serious relevant public health concern throughout the world despite related countermeasures being well understood (i.e. mainly physical activity and an adjusted diet). Among different nutritional approaches, there is a growing interest in ketogenic diets (KD) to manipulate body mass (BM) and to enhance fat mass loss. KD reduce the daily amount of carbohydrate intake drastically. This results in increased fatty acid utilisation, leading to an increase in blood ketone bodies (acetoacetate, 3-β-hydroxybutyrate and acetone) and therefore metabolic ketosis. For many years, nutritional intervention studies have focused on reducing dietary fat with little or conflicting positive results over the long term. Moreover, current nutritional guidelines for athletes propose carbohydrate-based diets to augment muscular adaptations. This review discusses the physiological basis of KD and their effects on BM reduction and body composition improvements in sedentary individuals combined with different types of exercise (resistance training or endurance training) in individuals with obesity and athletes. Ultimately, we discuss the strengths and the weaknesses of these nutritional interventions together with precautionary measures that should be observed in both individuals with obesity and athletic populations. A literature search from 1921 to April 2021 using Medline, Google Scholar, PubMed, Web of Science, Scopus and Sportdiscus Databases was used to identify relevant studies. In summary, based on the current evidence, KD are an efficient method to reduce BM and body fat in both individuals with obesity and athletes. However, these positive impacts are mainly because of the appetite suppressive effects of KD, which can decrease daily energy intake. Therefore, KD do not have any superior benefits to non-KD in BM and body fat loss in individuals with obesity and athletic populations in an isoenergetic situation. In sedentary individuals with obesity, it seems that fat-free mass (FFM) changes appear to be as great, if not greater, than decreases following a low-fat diet. In terms of lean mass, it seems that following a KD can cause FFM loss in resistance-trained individuals. In contrast, the FFM-preserving effects of KD are more efficient in endurance-trained compared with resistance-trained individuals.

Evaluating the Effects of Increased Protein Intake on Muscle Strength, Hypertrophy and Power Adaptations with Concurrent Training: A Narrative Review

Concurrent training incorporates dual exercise modalities, typically resistance and aerobic-based exercise, either in a single session or as part of a periodized training program, that can promote muscle strength, mass, power/force and aerobic capacity adaptations for the purposes of sports performance or general health/wellbeing. Despite multiple health and exercise performance-related benefits, diminished muscle hypertrophy, strength and power have been reported with concurrent training compared to resistance training in isolation. Dietary protein is well-established to facilitate skeletal muscle growth, repair and regeneration during recovery from exercise. The degree to which increased protein intake can amplify adaptation responses with resistance exercise, and to a lesser extent aerobic exercise, has been highly studied. In contrast, much less focus has been directed toward the capacity for protein to enhance anabolic and metabolic responses with divergent contractile stimuli inherent to concurrent training and potentially negate interference in muscle strength, power and hypertrophy. This review consolidates available literature investigating increased protein intake on rates of muscle protein synthesis, hypertrophy, strength and force/power adaptations following acute and chronic concurrent training. Acute concurrent exercise studies provide evidence for the significant stimulation of myofibrillar protein synthesis with protein compared to placebo ingestion. High protein intake can also augment increases in lean mass with chronic concurrent training, although these increases do not appear to translate into further improvements in strength adaptations. Similarly, the available evidence indicates protein intake twice the recommended intake and beyond does not rescue decrements in selective aspects of muscle force and power production with concurrent training.

Lean mass sparing in resistance-trained athletes during caloric restriction: the role of resistance training volume

Many sports employ caloric restriction (CR) to reduce athletes’ body mass. During these phases, resistance training (RT) volume is often reduced to accommodate recovery demands. Since RT volume is a well-known anabolic stimulus, this review investigates whether a higher training volume helps to spare lean mass during CR. A total of 15 studies met inclusion criteria. The extracted data allowed calculation of total tonnage lifted (repetitions × sets × intensity load) or weekly sets per muscle group for only 4 of the 15 studies, with RT volume being highly dependent on the examined muscle group as well as weekly training frequency per muscle group. Studies involving high RT volume programs (≥ 10 weekly sets per muscle group) revealed low-to-no (mostly female) lean mass loss. Additionally, studies increasing RT volume during CR over time appeared to demonstrate no-to-low lean mass loss when compared to studies reducing RT volume. Since data regarding RT variables applied were incomplete in most of the included studies, evidence is insufficient to conclude that a higher RT volume is better suited to spare lean mass during CR, although data seem to favor higher volumes in female athletes during CR. Moreover, the data appear to suggest that increasing RT volume during CR over time might be more effective in ameliorating CR-induced atrophy in both male and female resistance-trained athletes when compared to studies reducing RT volume. The effects of CR on lean mass sparing seem to be mediated by training experience, pre-diet volume, and energy deficit, with, on average, women tending to spare more lean mass than men. Potential explanatory mechanisms for enhanced lean mass sparing include a preserved endocrine milieu as well as heightened anabolic signaling.

Intermittent fasting and continuous energy restriction result in similar changes in body composition and muscle strength when combined with a 12 week resistance training program

Purpose

The objective of this study was to compare the effects of 12 weeks of resistance training combined with either 5:2 intermittent fasting or continuous energy restriction on body composition, muscle size and quality, and upper and lower body strength.

Methods

Untrained individuals undertook 12 weeks of resistance training plus either continuous energy restriction [20% daily energy restriction (CERT)] or 5:2 intermittent fasting [~ 70% energy restriction 2 days/week, euenergetic consumption 5 days/week (IFT)], with both groups prescribed a mean of ≥ 1.4 g of protein per kilogram of body weight per day. Participants completed 2 supervised resistance and 1 unsupervised aerobic/resistance training combination session per week. Changes in lean body mass (LBM), thigh muscle size and quality, strength and dietary intake were assessed.

Results

Thirty-four participants completed the study (CERT = 17, IFT = 17). LBM was significantly increased (+ 3.7%, p < 0.001) and body weight (− 4.6%, p < 0.001) and fat (− 24.1%, p < 0.001) were significantly reduced with no significant difference between groups, though results differed by sex. Both groups showed improvements in thigh muscle size and quality, and reduced intramuscular and subcutaneous fat assessed by ultrasonography and peripheral quantitative computed tomography (pQCT), respectively. The CERT group demonstrated a significant increase in muscle surface area assessed by pQCT compared to the IFT group. Similar gains in upper and lower body strength and muscular endurance were observed between groups.

Conclusion

When combined with resistance training and moderate protein intake, continuous energy restriction and 5:2 intermittent fasting resulted in similar improvements in body composition, muscle quality, and strength. ACTRN: ACTRN12620000920998, September 2020, retrospectively registered.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00394-022-02804-3.

Loss of Skeletal Muscle Mass and Intracellular Water as Undesired Outcomes of Weight Reduction in Obese Hyperglycemic Women: A Short-Term Longitudinal Study

The current study is focused on the influence of hyperglycemia on weight loss in obese premenopausal women. Specifically, the study evaluated the impact of a six-month individualized low-calorie diet combined with moderate exercise on weight reduction and glucose metabolism in obese women with normoglycemia compared to obese women with moderate hyperglycemia. The results indicated that patients with normoglycemia achieved a successful weight loss, which was connected to a decrease in adipose tissue and reflected by diminished content of visceral fat area (VFA) and percent body fat. In contrast, weight reduction in patients with hyperglycemia was connected not only to the loss of VFA but also to undesired decrease in skeletal muscle mass as well as intracellular and total body water. These unfavorable outcomes were observed despite normalization of glucose metabolism reflected by statistically significant lowering glucose, fructosamine, advanced glycation end-products, and HOMA-IR levels. Overall, the obtained results indicate the importance of the measurement of the carbohydrate profile in obese women and the need for an early introduction of weight reduction strategies before the development of hyperglycemia.

Weight loss and high-protein, high-fiber diet consumption impact blood metabolite profiles, body composition, voluntary physical activity, fecal microbiota, and fecal metabolites of adult dogs

Canine obesity is associated with reduced lifespan and metabolic dysfunction, but can be managed by dietary intervention. This study aimed to determine the effects of restricted feeding of a high-protein, high-fiber (HPHF) diet and weight loss on body composition, physical activity, blood metabolites, and fecal microbiota and metabolites of overweight dogs. Twelve spayed female dogs (age: 5.5 ± 1.1 yr; body weight [BW]: 14.8 ± 2.0 kg, body condition score [BCS]: 7.9 ± 0.8) were fed a HPHF diet during a 4-wk baseline phase to maintain BW. After baseline (week 0), dogs were first fed 80% of baseline intake and then adjusted to target 1.5% weekly weight loss for 24 wk. Body composition using dual-energy x-ray absorptiometry and blood samples (weeks 0, 6, 12, 18, and 24), voluntary physical activity (weeks 0, 7, 15, and 23), and fresh fecal samples for microbiota and metabolite analysis (weeks 0, 4, 8, 12, 16, 20, and 24) were measured over time. Microbiota data were analyzed using QIIME 2. All data were analyzed statistically over time using SAS 9.4. After 24 wk, dogs lost 31.2% of initial BW and had 1.43 ± 0.73% weight loss per week. BCS decreased (P < 0.0001) by 2.7 units, fat mass decreased (P < 0.0001) by 3.1 kg, and fat percentage decreased (P < 0.0001) by 11.7% with weight loss. Many serum metabolites and hormones were altered, with triglycerides, leptin, insulin, C-reactive protein, and interleukin-6 decreasing (P < 0.05) with weight loss. Relative abundances of fecal Bifidobacterium, Coriobacteriaceae UCG-002, undefined Muribaculaceae, Allobaculum, Eubacterium, Lachnospira, Negativivibacillus, Ruminococcus gauvreauii group, uncultured Erysipelotrichaceae, and Parasutterella increased (P < 0.05), whereas Prevotellaceae Ga6A1 group, Catenibacterium, Erysipelatoclostridium, Fusobacterium, Holdemanella, Lachnoclostridium, Lactobacillus, Megamonas, Peptoclostridium, Ruminococcus gnavus group, and Streptococcus decreased (P < 0.01) with weight loss. Despite the number of significant changes, a state of dysbiosis was not observed in overweight dogs. Fecal ammonia and secondary bile acids decreased, whereas fecal valerate increased with weight loss. Several correlations between gut microbial taxa and biological parameters were observed. Our results suggest that restricted feeding of a HPHF diet and weight loss promotes fat mass loss, minimizes lean mass loss, reduces inflammatory marker and triglyceride concentrations, and modulates fecal microbiota phylogeny and activity in overweight dogs.

Emerging role of MyomiRs as biomarkers and therapeutic targets in skeletal muscle diseases

Several chronic diseases lead to skeletal muscle loss and a decline in physical performance. MicroRNAs (miRNAs) are small, noncoding RNAs, which have exhibited their role in the development and diseased state of the skeletal muscle. miRNA regulates gene expression by binding to the 3' untranslated region of its target mRNA. Due to the robust stability in biological fluids, miRNAs are ideal candidate as biomarker. These miRNAs provide a novel avenue in strengthening our awareness and knowledge about the factors governing skeletal muscle functions such as development, growth, metabolism, differentiation, and cell proliferation. It also helps in understanding the therapeutic strategies in improving or conserving skeletal muscle health. This review outlines the evidence regarding the present knowledge on the role miRNA as a potential biomarker in skeletal muscle diseases and their exploration might be a unique and potential therapeutic strategy for various skeletal muscle disorders.

Dietary protein requirements and recommendations for healthy older adults: a critical narrative review of the scientific evidence

Adequate protein intake is essential for the maintenance of whole-body protein mass. Different methodological approaches are used to substantiate the evidence for the current protein recommendations, and it is continuously debated whether older adults require more protein to counteract the age-dependent loss of muscle mass, sarcopenia. Thus, the purpose of this critical narrative review is to outline and discuss differences in the approaches and methodologies assessing the protein requirements and, hence, resulting in controversies in current protein recommendations for healthy older adults. Through a literature search, this narrative review first summarises the historical development of the Food and Agriculture Organization/World Health Organization/United Nations University setting of protein requirements and recommendations for healthy older adults. Hereafter, we describe the various types of studies (epidemiological studies and protein turnover kinetic measurements) and applied methodological approaches founding the basis and the different recommendations with focus on healthy older adults. Finally, we discuss important factors to be considered in future studies to obtain evidence for international agreement on protein requirements and recommendations for healthy older adults. We conclude by proposing future directions to determine 'true' protein requirements and recommendations for healthy older adults.

Achieving an Optimal Fat Loss Phase in Resistance-Trained Athletes: A Narrative Review

Managing the body composition of athletes is a common practice in the field of sports nutrition. The loss of body weight (BW) in resistance-trained athletes is mainly conducted for aesthetic reasons (bodybuilding) or performance (powerlifting or weightlifting). The aim of this review is to provide dietary–nutritional strategies for the loss of fat mass in resistance-trained athletes. During the weight loss phase, the goal is to reduce the fat mass by maximizing the retention of fat-free mass. In this narrative review, the scientific literature is evaluated, and dietary–nutritional and supplementation recommendations for the weight loss phase of resistance-trained athletes are provided. Caloric intake should be set based on a target BW loss of 0.5–1.0%/week to maximize fat-free mass retention. Protein intake (2.2–3.0 g/kgBW/day) should be distributed throughout the day (3–6 meals), ensuring in each meal an adequate amount of protein (0.40–0.55 g/kgBW/meal) and including a meal within 2–3 h before and after training. Carbohydrate intake should be adapted to the level of activity of the athlete in order to training performance (2–5 g/kgBW/day). Caffeine (3–6 mg/kgBW/day) and creatine monohydrate (3–5 g/day) could be incorporated into the athlete’s diet due to their ergogenic effects in relation to resistance training. The intake of micronutrients complexes should be limited to special situations in which there is a real deficiency, and the athlete cannot consume through their diet.

Effects of Combined High-Protein Diet and Exercise Intervention on Cardiometabolic Health in Middle-Aged Obese Adults: A Randomized Controlled Trial

Background: Obesity is the main risk factor of cardiovascular diseases (CVD) and metabolic diseases. The middle-aged population is the age group with the highest prevalence of obesity. Thus, improving cardiometabolic health is important to prevent CVD and metabolic diseases in middle-aged obese adults. The aim of this study was to examine the effects of exercise alone or in combination with a high-protein diet on markers of cardiometabolic health in middle-aged adults with obesity.

Methods: Sixty-nine middle-aged adults with obesity were assigned randomly to the control group (C; n = 23), exercise group (E; n = 23), or exercise combined with high-protein diet group (EP; n = 23). Individuals in the E and EP groups received supervised exercise training and individuals in the EP group received high-protein diet intervention. Body composition (assessed by dual-energy X-ray absorptiometry), oral glucose tolerance test (OGTT), lipid profiles, and inflammatory markers were determined before and after 12 weeks of intervention. Insulin sensitivity index (ISI_0,120) was calculated from values of fasting and 2-h insulin and glucose concentration of OGTT. Insulin-peak-time during the OGTT was recorded to reflect β-cell function. Analysis of covariance with baseline values as covariates was used to examine the effects of the intervention. The significant level was set at 0.05.

Results: After 12 weeks of intervention, the E group had a greater percentage of individuals with early insulin-peak-time during the OGTT than that in the C and EP groups (p = 0.031). EP group had lower total cholesterol and triglycerides than that in the C group (p = 0.046 and 0.014, respectively). Within-group comparisons showed that the 2-h glucose of OGTT and C-reactive protein decreased in the EP group (p = 0.013 and 0.008, respectively) but not in the E and C groups; insulin sensitivity improved in the EP group (p = 0.016) and had a trend to improve in the E group (p = 0.052); and abdominal fat mass and total body fat mass decreased in both intervention groups (p < 0.05).

Conclusion: Combined high-protein diet and exercise intervention significantly decreased fat mass and improved lipid profiles, insulin sensitivity, glucose tolerance, and inflammation in middle-aged adults with obesity.

Clinical Trial Registration: Thai Clinical Trials Registry, TCTR20180913003, 13-09-2018.

Energy Restriction Suppresses Muscle Protein Synthesis, and High Protein Diets Extend Protein Half-Lives Across the Muscle Proteome in Obese Female Zucker Rats

BACKGROUND

Effects of high protein (HP) diets and prolonged energy restriction (ER) on integrated muscle protein kinetics have not been determined.

OBJECTIVE

The objective of this study was to measure protein kinetics in response to prolonged ER and HP on muscle protein synthesis (MPS; absolute rates of synthesis) and muscle protein breakdown (MPB; half-lives) for proteins across the muscle proteome.

METHODS

Female 6-wk-old obese Zucker rats (Leprfa+/fa+, n = 48) were randomly assigned to one of four diets for 10 wk: ad libitum-standard protein (AL-SP; 15% kcal from protein), AL-HP (35% kcal from protein), ER-SP, and ER-HP (both fed 60% feed consumed by AL-SP). During week 10, heavy/deuterated water (2H2O) was administered by intraperitoneal injection, and isotopic steady-state was maintained via 2H2O in drinking water. Rats were euthanized after 1 wk, and mixed-MPS as well as fractional replacement rate (FRR), relative concentrations, and half-lives of individual muscle proteins were quantified in the gastrocnemius. Data were analyzed using 2-factor (energy × protein) ANOVAs and 2-tailed t-tests or binomial tests as appropriate.

RESULTS

Absolute MPS was lower in ER than AL for mixed-MPS (-29.6%; P < 0.001) and MPS of most proteins measured [23/26 myofibrillar, 48/60 cytoplasmic, and 46/60 mitochondrial (P < 0.05)], corresponding with lower gastrocnemius mass in ER compared with AL (-29.4%; P < 0.001). Although mixed-muscle protein half-life was not different between groups, prolonged half-lives were observed for most individual proteins in HP compared with SP in ER and AL (P < 0.001), corresponding with greater gastrocnemius mass in HP than SP (+5.3%; P = 0.043).

CONCLUSIONS

ER decreased absolute bulk MPS and most individual MPS rates compared with AL, and HP prolonged half-lives of most proteins across the proteome. These data suggest that HP, independent of energy intake, may reduce MPB, and reductions in MPS may contribute to lower gastrocnemius mass during ER by reducing protein deposition in obese female Zucker rats.

Caloric Restriction per se Rather Than Dietary Macronutrient Distribution Plays a Primary Role in Metabolic Health and Body Composition Improvements in Obese Mice

Caloric restriction (CR) is of key importance in combating obesity and its associated diseases. We aimed to examine effects of dietary macronutrient distribution on weight loss and metabolic health in obese mice exposed to CR. Male C57BL/6J mice underwent diet-induced obesity for 18 weeks. Thereafter mice were exposed to a 6-week CR for up to 40% on either low-fat diet (LFD; 20, 60, 20% kcal from protein, carbohydrate, fat), low-carb diet (LCD; 20, 20, 60% kcal, respectively) or high-pro diet (HPD; 35, 35, 30% kcal, respectively) (n = 16 each). Ten mice on the obesogenic diet served as age-matched controls. Body composition was evaluated by tissue dissections. Glucose tolerance, bloods lipids and energy metabolism were measured. CR-induced weight loss was similar for LFD and LCD while HPD was associated with a greater weight loss than LCD. The diet groups did not differ from obese controls in hindlimb muscle mass, but showed a substantial decrease in body fat without differences between them. Glucose tolerance and blood total cholesterol were weight-loss dependent and mostly improved in LFD and HPD groups during CR. Blood triacylglycerol was lowered only in LCD group compared to obese controls. Thus, CR rather than macronutrient distribution in the diet plays the major role for improvements in body composition and glucose control in obese mice. Low-carbohydrate-high-fat diet more successfully reduces triacylglycerol but not cholesterol levels compared to isocaloric high-carbohydrate-low-fat weight loss diets.

Changes in energy balance, body composition, metabolic profile and physical performance in a 62-day Army Ranger training in a hot-humid environment

OBJECTIVES

To determine the physiological effects of multiple stressors including energy deficit during a 62-day Ranger course in a hot-humid environment.

DESIGN

Prospective cohort design.

METHODS

Food intake data were collected daily and energy expenditure at each of the three phases of the course was estimated by the doubly-labeled water method. Anthropometry, hydration status, stress and metabolic hormones, handgrip strength and lower explosive power were measured at the start and at the end of each phase.

RESULTS

Seventeen male participants (age: 24.5 ± 3.2 years, height: 173.9 ± 5.1 cm, body mass: 69.3 ± 3.2 kg, BMI: 22.9 ± 0.9 kg/m², percent body fat: 14 ± 5%) completed the study. Mean total daily energy expenditure was 4756 kcal/day and mean daily energy intake was 3882 kcal/day. An 18% energy deficit resulted in an average body mass loss of 4.6 kg, comprising mostly fat mass. Participants with higher baseline adiposity (>15% body fat) lost more fat mass and gained (rather than lost) muscle mass compared to those with lower baseline adiposity. Handgrip strength declined only at the end of Phase I, while lower body explosive power declined progressively throughout the course. Lean mass in arms and legs was correlated with initial grip strength and lower body explosive power, but only at the start of the course.

CONCLUSIONS

Physiologically demanding Ranger training in an equatorial environment is at least as metabolically demanding and stressful as other similar high-risk training courses, as demonstrated by the stress and metabolic endocrine responses, changes in body composition, and reduction in explosive power. Moreover, the smaller body size of Asian soldiers may confer an energetic advantage over larger sized Western counterparts.

Ramadan Fasting Improves Body Composition without Exacerbating Depression in Males with Diagnosed Major Depressive Disorders

Background: Ramadan fasting (RF) is a form of intermittent fasting that generally improves body composition and related metabolic profiles. Whether RF exacerbates depressive symptomatology in individuals diagnosed with major depressive disorder (MDD) is undetermined. Methods: 100 men, who lived in Bahrain and were between the ages of 18 and 64 years with an established diagnosis of MDD, participated in this 4-week study. Based on preference, participants were assigned to a fasting group (FG, n = 50) and a non-fasting group (NFG, n = 50). The FG engaged in fasting from 03:40 to 18:10 (dawn and dusk timings). Changes in depressive symptoms, body mass, body composition, and components of metabolic syndrome were measured. Results: There were no significant changes in depressive symptoms within the FG vs. NFG after controlling for baseline covariates: mean difference 0.49 (SE = 0.63), p = 0.43. No adverse effects were reported in either group. The FG experienced significant reductions in body mass, 1.87 kg, p = 0.001; body mass index, 0.69 kg/m², p = 0.001; body fat, 0.87%, p = 0.001; body surface area, 0.03 m², p = 0.001; and lean mass, 0.77 kg, p = 0.001. Conclusions: RF did not negatively affect depressive symptoms and improved body composition, suggesting short-term intermittent fasting may be a safe dietary practice for adult males with MDD.

Weight Loss Strategies and the Risk of Skeletal Muscle Mass Loss

With energy intake restriction and exercise remaining the key diet and lifestyle approaches to weight loss, this is not without potential negative implications for body composition, metabolic health, and quality and quantity of life. Ideally, weight loss should be derived almost exclusively from the fat mass compartment as this is the main driver of metabolic disease, however, several studies have shown that there is an accompanying loss of tissue from the fat-free compartment, especially skeletal muscle. Population groups including post-menopausal women, the elderly, those with metabolic disease and athletes may be particularly at risk of skeletal muscle loss when following a weight management programme. Research studies that have addressed this issue across a range of population groups are reviewed with a focus upon the contribution of resistance and endurance forms of exercise and a higher intake dietary protein above the current guideline of 0.8 g/kg body weight/day. While findings can be contradictory, overall, the consensus appears that fat-free and skeletal muscle masses can be preserved, albeit to varying degrees by including both forms of exercise (but especially resistance forms) in the weight management intervention. Equally, higher intakes of protein can protect loss of these body compartments, acting either separately or synergistically with exercise. Elderly individuals in particular may benefit most from this approach. Thus, the evidence supports the recommendations for intakes of protein above the current guidelines of 0.8 g/kg body weight/d for the healthy elderly population to also be incorporated into the dietary prescription for weight management in this age group.

Mediterranean diet - promotion and dissemination of healthy eating: proceedings of an exploratory seminar at the Radcliffe institute for advanced study

The traditional Mediterranean diet is considered the world's most evidence-based eating pattern for promoting health and longevity. However, institutional food environments and their busy consumers often sacrifice health benefits for the convenience of faster and cheaper foods that generally are of lower quality and are more processed, and thus, contribute to the current epidemics of obesity and diabetes. Expert consensus has even identified the Mediterranean diet as the easiest to follow among healthy eating patterns. Nonetheless, fewer American families cook at home and many food services have been slow to implement healthier food options compatible with the Mediterranean diet. In September 2019, we convened a group of thought leaders at an exploratory seminar entitled: "Mediterranean Diet: Promotion and Dissemination of Healthy Eating", hosted by the Radcliffe Institute for Advanced Studies at Harvard University. The multidisciplinary faculty discussed best practices for translating traditional Mediterranean lifestyle principles to modern society.

Effects of 6 Months of Soy-Enriched High Protein Compared to Eucaloric Low Protein Snack Replacement on Appetite, Dietary Intake, and Body Composition in Normal-Weight Obese Women: A Randomized Controlled Trial

(1) Background: The favorable effects of high protein snacks on body composition and appetite status in lean and athletic populations have been illustrated previously. However, the effects of soy-enriched high protein snacks have not been investigated in women with normal-weight obesity (NWO). Consequently, we aimed at comparing the effects of six months of soy-enriched high protein snack replacement on appetite, body composition, and dietary intake in women with NWO. (2) Methods: One hundred seven (107) women with NWO [(age: 24 ± 3 yrs, BMI: 22.7 ± 2.3 kg/m², body fat percentage (BFP): 38 ± 3.2%)] who were assigned to one of two groups; high protein snack (HP, n = 52) containing 50 g soybean or isocaloric low-protein snack (protein: 18.2 g, carbohydrate: 15 g, fat: 10 g, energy: 210 kcal) or isocaloric low protein snack (LP, n = 55) containing 3.5 servings of fruit (protein: <2 g, carbohydrate: ≈50 g, fat: <1 g, energy: ≈210 kcal) as part of their daily meals (as a snack at 10 a.m.), successfully completed the study interventions. Body mass (BM), body mass index (BMI), waist circumference (WC), BFP, skeletal muscle mass, dietary intake, and appetite levels were evaluated prior to and after the six-month intervention. (3) Results: Appetite (HP = -12 mm and LP = -0.6 mm), energy intake (HP = -166.2 kcal/day and LP = 91.3 kcal), carbohydrate intake (HP = -58.4 g/day and LP = 6.4 g/day), WC (HP = -4.3 cm and LP = -0.9 cm), and BFP (HP = -3.7% and LP = -0.9%) were significantly (p < 0.05) reduced, while skeletal muscle mass (HP = 1.2 kg and LP = 0.3 kg) significantly increased in the HP compared to the LP group, respectively. (4) Conclusions: Six months of a soy-enriched high protein snack replacement decreased appetite and improved body composition in women with NWO. Our findings suggest that soy-enriched high protein snacks are an efficacious strategy for body composition improvement.

Flexible vs. rigid dieting in resistance-trained individuals seeking to optimize their physiques: A randomized controlled trial

Abstract

Background

The purpose of this study was to compare a flexible vs. rigid diet on weight loss and subsequent weight regain in resistance-trained (RT) participants in a randomized, parallel group design.

Methods

Twenty-three males and females (25.6 ± 6.1 yrs; 170 ± 8.1 cm; 75.4 ± 10.3 kg) completed the 20-week intervention (consisting of a 10-week diet phase and a 10-week post-diet phase). Participants were randomized to a flexible diet (FLEX) comprised of non-specific foods or a rigid diet (RIGID) comprised of specific foods. Participants adhered to an ~20%kcal reduction during the first 10-weeks of the intervention and were instructed to eat ad libitum for the final 10-weeks. Body composition and resting metabolic rate were assessed 5 times: (baseline, 5, 10 [end of diet phase], 16, and 20 weeks).

Results

During the 10-week diet phase, both groups significantly reduced bodyweight (FLEX: baseline = 76.1 ± 8.4kg, post-diet = 73.5 ± 8.8 kg, ▲2.6 kg; RIGID: baseline = 74.9 ± 12.2 kg, post-diet = 71.9 ± 11.7 kg, ▲3.0 kg, p < 0.001); fat mass (FLEX: baseline = 14.8 ± 5.7 kg, post-diet = 12.5 ± 5.0 kg, ▲2.3 kg; RIGID: baseline = 18.1 ± 6.2 kg, post-diet = 14.9 ± 6.5 kg, ▲3.2 kg p < 0.001) and body fat% (FLEX: baseline = 19.4 ± 8.5%, post-diet = 17.0 ± 7.1%, ▲2.4%; RIGID: baseline = 24.0 ± 6.2%, post-diet = 20.7 ± 7.1%, ▲3.3%; p < 0.001). There were no significant differences between the two groups for any variable during the diet phase. During the post-diet phase, a significant diet x time interaction (p < 0.001) was observed for FFM with the FLEX group gaining a greater amount of FFM (+1.7 kg) in comparison with the RIGID group (−0.7 kg).

Conclusions

A flexible or rigid diet strategy is equally effective for weight loss during a caloric restriction diet in free-living, RT individuals. While post-diet FFM gains were greater in the FLEX group, there were no significant differences in the amount of time spent in resistance and aerobic exercise modes nor were there any significant differences in protein and total caloric intakes between the two diet groups. In the absence of a clear physiological rationale for increases in FFM, in addition to the lack of a standardized diet during the post-diet phase, we refrain from attributing the increases in FFM in the FLEX group to their diet assignment during the diet phase of the investigation. We recommend future research investigate additional physiological and psychological effects of flexible diets and weight regain in lean individuals.

Association between dietary protein intake and skeletal muscle mass in older Korean adults

PURPOSE

We investigated the association of low and high daily protein intakes on skeletal muscle mass status in Korean adults aged 60 years and older.

METHODS

This cross-sectional study used data from the Korean National Health and Nutrition Examination Survey conducted between 2008 and 2011. The participants' dietary protein intake was assessed using the 24-h dietary recall method and was classified as low (< 0.8 g/kg body weight/day), moderate (0.8-1.2 g/kg/day), and high (> 1.2 g/kg/day). Amount of skeletal muscle mass was measured using whole-body dual-energy X-ray absorptiometry. Low skeletal muscle mass was defined as appendicular skeletal muscle mass index < 7.0 kg/m² in men and < 5.4 kg/m² in women.

RESULTS

The study included data from 4585 participants (2022 men and 2563 women). All skeletal muscle parameters in women and total lean mass in men decreased as the amount of protein consumed daily increased. However, there was no association between high or low protein intake and low skeletal muscle mass in men or women.

CONCLUSIONS

No association was found between the amount of daily protein intake and skeletal muscle mass status in older Korean adults. Gender-specific further studies focussing on the interactions of dietary protein intake under specific conditions including physical activity status and the daily distribution of protein intake and the quality and source of the protein are needed to evaluate the impact of protein intake status on muscle health in older Koreans.