Inadequate protein intake affects skeletal muscle transcript profiles in older humans

Sarcopenia in Parkinson's disease: from pathogenesis to interventions

Parkinson's disease (PD) and sarcopenia are prevalent age-related conditions that often coexist in affected individuals. Sarcopenia is particularly common among PD patients, with severe cases affecting approximately one in five individuals with the disease. Furthermore, sarcopenia is closely linked to the accelerated progression of PD, diminished quality of life, greater susceptibility to falls and fractures, and increased mortality risk. Although the precise mechanisms remain unclear, numerous studies suggest that factors such as the accumulation of α-Synuclein in skeletal muscle, loss of motor neurons, inflammation, phosphate toxicity, hormonal dysregulation, vitamin D deficiency, intestinal flora imbalances, and dysfunction of the gut-muscle-brain axis contribute to sarcopenia in PD. Understanding these mechanisms provides valuable insights into the relationship between PD and sarcopenia and establishes a foundation for future research and therapeutic strategies. This review examines the mechanisms underlying sarcopenia in PD, methods for its screening and assessment, and potential avenues for future research, including strategies for risk reduction and treatment.

The Impact of Bariatric Surgery on Nitrogen Balance at Six months Post-surgery

PURPOSE

Obesity, defined as abnormal or excessive fat accumulation that presents a risk to health, rose from 8.6 to 10.5% in Singapore's residents. Bariatric surgery, the primary treatment for severe obesity, induces fat and muscle loss. Adequate protein intake is vital for preventing muscle loss. This study examines nitrogen balance in individuals with obesity pre- and post-surgery.

MATERIALS AND METHODS

Sixteen participants with severe obesity (BMI ≥ 32.5 kg/m2) undergoing bariatric surgery (14 sleeve gastrectomy, 2 Roux-en-Y gastric bypass) and 20 normal-weight controls (BMI < 25 kg/m2) were recruited. Nitrogen balance, calculated from dietary protein intake and urine nitrogen excretion, was assessed. Participants with obesity were re-evaluated 6 months post-surgery. Data were analyzed using parametric methods.

RESULTS

At baseline, controls had a BMI of 20.8 ± 2.1 kg/m2; those with obesity had 40.9 ± 7.3. Daily calorie and protein intake for participants with obesity were not statistically significantly different from controls (calorie intake at 1467 ± 430 vs. 1462 ± 391 kcal, p = 0.9701, protein intake 74.2 ± 28.7 vs. 64.6 ± 18.3 g, p = 0.2289). Post-surgery, BMI, fat-free mass, fat mass, total energy intake, carbohydrate, and protein intake decreased significantly (p < 0.01). Protein oxidation and urine nitrogen excretion did not change after bariatric surgery. However, nitrogen balance significantly reduced from 2.62 ± 5.07 to - 1.69 ± 5.07 g/day (p = 0.025).

CONCLUSION

Dietary protein intake is inadequate in individuals with obesity at 6 months post-bariatric surgery and contributes to a state of negative nitrogen balance.

Transcriptomic Analysis of Human Skeletal Muscle in Response to Aerobic Exercise and Protein Intake

This study aimed to provide a more comprehensive molecular insight into the effects of aerobic exercise (AE), protein intake (PI), and AE combined with PI on human skeletal muscle by comparing their transcriptomic profiles. Fourteen published datasets obtained from the Gene Expression Omnibus (GEO) database were used. The hub genes were identified in response to acute AE (ACTB, IL6), training AE (UBB, COL1A1), PI (EZH2), acute AE combined with PI (DDIT3), and training AE combined with PI (MYC). Both FOS and MYC were upregulated in response to acute AE, and they were, respectively, downregulated by higher PI and a combination of AE and PI. COL1A1 was upregulated by training AE but was downregulated by higher PI. Results from the gene set enrichment analysis (p < 0.05 and FDR < 25%) showed that AE and PI delivered their impacts on human skeletal muscle in analogous pathways, including aerobic respiration, mitochondrial complexes, extracellular matrix (ECM) remodeling, metabolic process, and immune/inflammatory responses, whereas, PI may attenuate the response of immune/inflammation and ECM remodeling which would be promoted by AE, irrespective of its types. Compared to PI alone, acute AE combined with PI would further promote protein turnover and synthesis, but suppress skeletal muscle contraction and movement.

Sarcopenia in youth

Recent research has revealed causes other than aging that may induce sarcopenia in young people, contrary to the long-studied age-dependent reduction in muscular mass and function. The risk of sarcopenia begins in early adulthood, resulting in exaggerated muscle dysfunction in later life. Despite its clinical significance, research on youth-onset sarcopenia is still in its infancy. Due to a paucity of epidemiologic data and standardized criteria for sarcopenia in youth, determining the prevalence of sarcopenia in the young population remains challenging. Based on the evidence, >1 in every 10 young adults of most ethnicities is estimated to have sarcopenia. This review summarizes the possible etiologies of sarcopenia in young populations, including metabolic syndrome, physical inactivity, inadequate nutrition, inherent and perinatal factors, vitamin D deficiency, endocrinopathy, an imbalance of gut microbiota, neuromuscular diseases, organ failure, malignancy, and other inflammatory disorders. This is the first review of the current knowledge on the importance, prevalence, diagnosis, and causes of sarcopenia in youth.

Increased Intake of Omega-3 Polyunsaturated Fatty Acids Is Associated with Reduced Odds of Low Hand Grip Strength in Korean Adults

Nutritional status is thought to be one of the modifiable risk factors for muscle health. This study investigates the association between dietary omega-3 polyunsaturated fatty acids (PUFA) intake and hand grip strength (HGS) in Korean adults. The cross-sectional analysis was performed on 18,278 participants aged ≥19 years enrolled in the Korea National Health and Nutrition Examination Survey from 2016-2019. Omega-3 PUFA consumption was positively linked to the dietary intake of nuts, fish, and shellfish in Korean adults. After adjusting for potential confounders, the results showed that increased omega-3 PUFA intake was associated with a decreased risk of low HGS (odds ratio (OR) for upper quartile (Q4) compared to Q1, men: OR = 1.42 (95% CI: 1.17-1.72), women: OR = 1.61 (1.37-1.89)). This inverse association was reported in people who did no resistance exercise or had an insufficient protein intake. In contrast, this association was not evident in adults who did resistance exercise or had sufficient protein intake. Furthermore, participants with hypertension or type 2 diabetes showed stronger associations between dietary omega-3 PUFA intake and HGS compared with other subgroups. These results suggest that dietary omega-3 PUFA intake positively related with HGS in Korean adults.

Daily Dietary Supplementation with Steamed Soybean Improves Muscle Volume and Strength in Healthy People Lacking Exercise

Various dietary protein supplements are used by the elderly and bedridden to maintain their skeletal muscle mass and functions. High-quality proteins act as an anabolic driver and help to improve muscle strength and performance. Previously, we reported that soy protein significantly attenuates denervation-induced loss of muscle mass and myofiber cross sectional area in mice with inhibition of ubiquitination and degradation of IRS-1 in tibialis anterior muscle. It also increased muscle volume and strength in bedridden patients. In the present study, we investigated the effects of dietary soybean supplementation on muscle functions in taxi drivers lacking vigorous physical exercise. We conducted a case-control study on 25 healthy, male taxi drivers between the ages of 36 and 71 y performing minimal physical exercise. They were divided into two dietary groups: the soybean diet group (n=13) who ate daily meals (dinner) supplemented with 50 g of steamed soybean for 30 d and the control diet group (n=12) who received no soybean supplement. Next, we measured the muscle cross-sectional area (CSA) and muscle strength and function in both the groups before and after 30 d of soybean intake. The body weights of both diet groups did not differ significantly over time. However, after 30 d of soybean supplementation, the soybean-fed group developed significantly higher muscle CSA and grip strength compared to the control groups. In conclusion, dietary soybean supplementation improved muscle function in taxi drivers who lacked exercise.

Association between food texture levels consumed and the prevalence of malnutrition and sarcopenia in older patients after stroke

BACKGROUND/OBJECTIVES

Texture-modified diets (TMDs) may affect nutritional status and sarcopenia in patients after stroke. This study aimed to investigate the association of food texture levels consumed by patients after stroke with the prevalence of malnutrition and sarcopenia.

SUBJECTS/METHODS

This was a two-center cross-sectional study. A total of 443 patients aged ≥65 years undergoing post-stroke rehabilitation and with oral intake in rehabilitation wards in Shizuoka prefecture and Okinawa prefecture, Japan, were included in the analysis. Food textures were categorized according to the International Dysphagia Diet Standardization Initiative (IDDSI) framework. Malnutrition was diagnosed according to the Global Leadership Initiative on Malnutrition and sarcopenia was assess by the European Working Group on Sarcopenia in Older People 2 criteria. The Cochran-Armitage trend test was used to examine the prevalence of malnutrition and sarcopenia by consumption of lower food texture levels.

RESULTS

Malnutrition and sarcopenia were diagnosed in 245 (55.3%) and 275 (62.1%) participants, respectively. Consumption of lower food texture levels was associated with a higher prevalence of malnutrition and severe malnutrition (P < 0.001 for both). In addition, consumption of lower food texture levels was associated with a higher prevalence of probable sarcopenia and sarcopenia (P < 0.001 for both). On multivariate analysis, significant associations were observed between IDDSI levels 5 (P < 0.001) and 4 (P = 0.009) and malnutrition, and between IDDSI levels 6 (P = 0.015), 5 (P = 0.033), and 4 (P = 0.015) and sarcopenia.

CONCLUSIONS

In patients with stroke, consumption of lower food texture levels categorized by the IDDSI framework was associated with a higher prevalence of malnutrition and sarcopenia.

Association between total protein intake and low muscle mass in Korean adults

Background

Adults with low muscle mass have a poor prognosis. Studies that examined the association between total protein intake and low muscle mass among adults are limited. Thus, we investigated the association between total protein intake and low muscle mass among Korean adults aged ≥19 years.

Methods

We included 15,995 adults (6528 male and 9467 female) aged ≥19 years from the Korea National Health and Nutrition Examination Surveys (2008–2011). We divided the participants into groups according to protein intake quartile: Q1, Q2, Q3 and Q4 groups. The odds ratios (ORs) and 95% confidence intervals (CIs) of low muscle mass according to protein intake were analysed via multivariable logistic regression analysis. Stratified analyses according to sex, age and comorbidities were also performed.

Results

Of the participants, 3.8% had weight-adjusted low muscle mass. The prevalence rates of low muscle mass were 1.5, 3.0, 3.9 and 7.2% in the Q4, Q3, Q2 and Q1 groups, respectively (p < 0.001). Compared with the Q4 group, the Q1 group had the highest ORs for low muscle mass, followed by the Q2 and Q3 groups (Model 5; OR, 95% CI: 2.03, 1.36–3.02 for Q3; 2.44, 1.64–3.61 for Q2; and 4.32, 2.89–6.45 for Q4) after adjusting for confounding variables (p for trend < 0.001). The associations between protein intake and low muscle mass were stronger in younger individuals, men, individuals without hypertension, those with diabetes mellitus and those without dyslipidemia.

Conclusions

The prevalence of low muscle mass in Korean adults significantly increased with lower protein intake. Nutrition education for proper protein intake is also important for adults.

Trial registration

Retrospectively registered.

Guava Fruit and Acacia pennata Vegetable Intake Association with Frailty of Older Adults in Northern Thailand

As Thailand moves toward an aging society, frailty has become a concern amongst northern Thai elderly. The causes of frailty are multifactorial and include genetic, environmental, and socio-economic factors; diet is of particular interest. A cross-sectional study was conducted from September to October 2017 to investigate what kind of diets normally consumed by 350 Thai elders were associated with frailty using a questionnaire and frailty determination by Fried’s phenotype followed by phytochemical analyses of the diets. The multivariable logistic regression analysis demonstrated a significant positive association between certain foods and lower frailty. Guava fruit and Acacia pennata vegetable consumption had lower odds of frailty, which were 0.52 times (95% CI 0.28−0.96, p = 0.037) and 0.42 times (95% CI 0.21−0.83, p = 0.012) when adjusted for the potential confounders. The phytochemical analyses of guava fruit showed a significantly higher amount of total flavonoids (p < 0.001), total phenolic compounds (p = 0.002), and antioxidant capacity, including DPPH (p < 0.001), ABTS (p < 0.001), and FRAP (p = 0.002) when compared to those of banana. Acacia pennata vegetable contained a significantly higher amount of total phenolic compounds (p = 0.012) when compared to those of lettuce. These findings may assist in health promotion programs of frailty prevention by encouraging an increase in consumption of either guava fruit or Acacia pennata vegetable among Thai elderly.

Effect of Whey Protein Supplementation on Perioperative Outcomes in Patients with Cancer-A Systematic Review and Meta-Analysis (PROSPERO 2020: CRD42020188666)

Whey protein has several biochemical characteristics which make it an ideal nutritional supplement in cancer. This meta-analysis aims to evaluate the effects of whey on perioperative outcomes in cancer. A systematic review was conducted as per the Preferred Reporting of Systematic Reviews and Meta-analysis (PRISMA) guidelines. The primary outcome was postoperative complications. Secondary outcomes included 6-minute walk test, length of stay (LOS), and thirty-day readmission. Of the ten trials, six supplemented whey to meet protein requirements of around 1.2 mg/kg/day, and four supplemented whey variably. A synthesis of ten trials with 643 patients showed significantly decreased postoperative complications in the whey supplemented (22%) group as compared to the control (32%) (OR 0.61, 95% CI 0.41-0.90; P = 0.01). Analysis of six trials showed that patients supplemented with whey had greater functional walking capacity before surgery (MD 23.76 meters, 95% CI 4.05-43.47; participants = 377; P = 0.02) and after 4 weeks of surgery (MD 45.76, 95% CI 14.19-77.33; participants = 366; P = 0.004). Thirty-day readmissions and LOS showed no differences. Risk of bias varied between the trials and evidence was moderate to low. Whey protein supplementation improved the perioperative functional capacity and significantly reduced postoperative complications in patients with cancer.

Association between frailty and dietary quality in community-dwelling elderly: data from the 6th Korea National Health and Nutrition Examination Survey (2014-2015)

Frailty is a progressive age-related disorder associated with odds ratio for subsequent falls, disability, and mortality. This study analyzed the association between frailty odds ratios and diet quality using the Korean Healthy Eating Index in older individuals. Data were obtained for 2,660 community-dwelling individuals aged ≥60 years who participated in the 6th Korea National Health and Nutrition Survey (2014-2015). Frailty was diagnosed following the Fried phenotype index based on five criteria: unintentional weight loss, emotional exhaustion, low physical activity, slow walking speed, and weak grip strength. The participants were categorized as normal, pre-frail, and frail. Diet quality was assessed using Korean Healthy Eating Index scores calculated based on 24-h dietary recall. Compared to the group with the highest Korean Healthy Eating Index score, the group with low Korean Healthy Eating Index showed a 1.71-fold higher pre-frail odds ratio (95% CI 1.31-2.22, p<0.001) and 1.87-fold higher frail odds ratio (95% CI 1.21-2.91, p = 0.009). Also, compared to the group with the highest adequacy score, the group with the lowest score showed a 1.51-fold higher pre-frail odds ratio (95% CI 1.16-1.96, p = 0.010) and a 2.39-fold higher frail odds ratio (95% CI 1.48-3.86, p = 0.002). The findings of this study suggested that a high-quality diet, as assessed by Korean Healthy Eating Index, was negatively associated with the odds ratio of frailty.

Factors influencing the efficacy of nutritional interventions on muscle mass in older adults: a systematic review and meta-analysis

CONTEXT

Nutritional interventions stimulate muscle protein synthesis in older adults. To optimize muscle mass preservation and gains, several factors, including type, dose, frequency, timing, duration, and adherence have to be considered.

OBJECTIVE

This systematic review and meta-analysis aimed to summarize these factors influencing the efficacy of nutritional interventions on muscle mass in older adults.

DATA SOURCES

A systematic search was performed using the electronic databases MEDLINE, Embase, CINAHL, Cochrane Central Register of Controlled Trials, and SPORTDiscus from inception date to November 22, 2017, in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Inclusion criteria included randomized controlled trials, mean or median age ≥65 years, and reporting muscle mass at baseline and postintervention. Exclusion criteria included genetically inherited diseases, anabolic drugs or hormone therapies, neuromuscular electrical stimulation, chronic kidney disease, kidney failure, neuromuscular disorders, and cancer.

DATA EXTRACTION

Extracted data included study characteristics (ie, population, sample size, age, sex), muscle mass measurements (ie, method, measure, unit), effect of the intervention vs the control group, and nutritional intervention factors (ie, type, composition, dose, duration, frequency, timing, and adherence).

DATA ANALYSIS

Standardized mean differences and 95%CIs were calculated from baseline to postintervention. A meta-analysis was performed using a random-effects model and grouped by the type of intervention.

CONCLUSIONS

Twenty-nine studies were included, encompassing 2255 participants (mean age, 78.1 years; SD, 2.22). Amino acids, creatine, β-hydroxy-β-methylbutyrate, and protein with amino acids supplementation significantly improved muscle mass. No effect was found for protein supplementation alone, protein and other components, and polyunsaturated fatty acids. High interstudy variability was observed regarding the dose, duration, and frequency, coupled with inconsistency in reporting timing and adherence. Overall, several nutritional interventions could be effective to improve muscle mass measures in older adults. Because of the substantial variability of the intervention factors among studies, the optimum profile is yet to be established.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration no. CRD42018111306.

A Novel Dietary Intervention Reduces Circulatory Branched-Chain Amino Acids by 50%: A Pilot Study of Relevance for Obesity and Diabetes

Elevated circulating branched-chain amino acids (BCAAs; isoleucine, leucine, and valine) are associated with obesity and type 2 diabetes (T2D). Reducing circulatory BCAAs by dietary restriction was suggested to mitigate these risks in rodent models, but this is a challenging paradigm to deliver in humans. We aimed to design and assess the feasibility of a diet aimed at reducing circulating BCAA concentrations in humans, while maintaining energy balance and overall energy/protein intake. Twelve healthy individuals were assigned to either a 7-day BCAA-restricted diet or a 7-day control diet. Diets were iso-nitrogenous and iso-caloric, with only BCAA levels differing between the two. The BCAA-restricted diet significantly reduced circulating BCAA concentrations by ~50% i.e., baseline 437 ± 60 to 217 ± 40 µmol/L (p < 0.005). Individually, both valine (245 ± 33 to 105 ± 23 µmol/L; p < 0.0001), and leucine (130 ± 20 to 75 ± 13 µmol/L; p < 0.05), decreased significantly in response to the BCAA-restricted diet. The BCAA-restricted diet marginally lowered Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) levels: baseline 1.5 ± 0.2 to 1.0 ± 0.1; (p = 0.096). We successfully lowered circulating BCAAs by 50% while maintaining iso-nitrogenous, iso-caloric dietary intakes, and while meeting the recommended daily allowances (RDA) for protein requirements. The present pilot study represents a novel dietary means by which to reduce BCAA, and as such, provides a blueprint for a potential dietary therapeutic in obesity/diabetes.

Neuromuscular Junction as an Entity of Nerve-Muscle Communication

One of the crucial systems severely affected in several neuromuscular diseases is the loss of effective connection between muscle and nerve, leading to a pathological non-communication between the two tissues. The neuromuscular junction (NMJ) represents the critical region at the level of which muscle and nerve communicate. Defects in signal transmission between terminal nerve endings and muscle membrane is a common feature of several physio-pathologic conditions including aging and Amyotrophic Lateral Sclerosis (ALS). Nevertheless, controversy exists on whether pathological events beginning at the NMJ precede or follow loss of motor units. In this review, the role of NMJ in the physio-pathologic interplay between muscle and nerve is discussed.

Amount Rather than Animal vs Plant Protein Intake Is Associated with Skeletal Muscle Mass in Community-Dwelling Middle-Aged and Older Chinese Adults: Results from the Guangzhou Nutrition and Health Study

BACKGROUND

Current literature does not indicate if the amount and animal vs plant protein are equally important in the prevention of muscle loss in middle-aged and older Chinese adults.

OBJECTIVE

The aim of the study was to examine the associations between amount or animal vs plant protein and skeletal muscle mass in Chinese adults aged 40 to 80 years.

DESIGN

A cross-sectional analysis of a prospective, community-based cohort was performed.

PARTICIPANTS/SETTING

Participants included 1,044 men and 2,169 women aged 40 to 80 years from the Guangzhou Nutrition and Health Study 2011-2013 with body composition measurements by dual-energy x-ray absorptiometry.

MAIN OUTCOME MEASURE

The skeletal muscle index (SMI) was defined as appendicular skeletal muscle mass divided by body weight. Participants in the lowest quartile of the sex-specific SMI were considered to have low muscle mass (LMM).

STATISTICAL ANALYSIS

Analyses of covariance were performed to estimate the SMI across quintiles of relative dietary intake of total, animal, and plant protein and the ratio of animal-to-plant protein. Logistic regression models were applied to assess the associations between quintiles of protein intake and LMM.

RESULTS

The SMI increased significantly across quintiles of relative dietary intake of total, animal, and plant protein (all P trends<0.001). Odds ratios (95% CIs) for LMM among participants in the highest (vs lowest) quintile were 0.3 (0.2, 0.4) for total protein, 0.3 (0.2, 0.5) for animal protein, and 0.4 (0.3, 0.7) for plant protein, respectively (all P trends<0.001). However, the ratio of animal-to-plant protein was not associated with either the SMI or the presence of LMM.

CONCLUSION

Higher dietary intakes of total, animal, and plant protein, regardless of the ratio of animal-to-plant protein, are associated with greater skeletal muscle mass in community-dwelling middle-aged and older Chinese adults with a mean protein intake above the current recommendation for protein of 0.8 g/kg per day.

Associations between muscle mass, physical activity and dietary behaviour in adolescents

BACKGROUND AND OBJECTIVES

Investigations in older individuals suggest that adequate nutrition and physical activity are particularly important to skeletal muscle health; however, data in adolescents are scant and equivocal. The objective was to determine the associations among diet, physical activity and skeletal muscle mass in adolescents.

METHODS

We assessed diet with four to seven 24-h recalls and physical activity by accelerometry in 640 adolescents. Using total body measures of fat-free soft tissue mass and fat mass assessed by dual-energy X-ray absorptiometry, the skeletal muscle mass index (SMMI) was derived by adjusting fat-free soft tissue mass for fat mass in addition to height.

RESULTS

Skeletal muscle mass index (SMMI) was negatively associated with consumption of sugar-sweetened beverages (standardized beta coefficient [β] = -0.10, P = 0.001) and saturated fats (β = -0.28, P < 0.001). SMMI was positively associated with physical activity (moderate + vigorous) (β = 0.20, P < 0.001). In further analysis, we observed a significant interaction between physical activity and sugar-sweetened beverage intake on SMMI (P = 0.002).

CONCLUSION

Our study in adolescence suggests that physical activity and consumption of both sugar-sweetened beverages and saturated fats are associated with skeletal muscle mass. More importantly, our findings suggest that sugar-sweetened beverage intake may attenuate the beneficial effects of physical activity on skeletal muscle mass.

Does Protein Intake Affect Metabolic Risk Factors among Older Adults in Korea?

Background

Carbohydrate intake can impact metabolic risk factors, but related research on protein intake in the elderly is rare. Our purpose was to estimate protein intake and explore how different levels of protein intake influence metabolic risk factors in Korean older adults.

Methods

Data were obtained from men aged 51-70 years (n=1,735), men aged ≥71 years (n=700), women aged 51-70 years (n=2,305), and women aged ≥71 years (n=957). Health and dietary data were obtained from the Korean National Health and Nutrition Examination Survey of 2010-2011.

Results

Relative to the recommended protein intake based on the Dietary Reference Intakes for Koreans, inadequate intake was higher in women and super-aging groups than in others. Women had an increased risk of having metabolic risk factors. After adjustment for age and sex, compared with those in the highest quartile of protein intake levels (>1.2 g protein/kg body weight/day), participants in the lowest quartile (<0.8 g protein/kg body weight/day) had increased odds ratios (ORs) for abdominal obesity (men: OR, 2.67; 95% confidence interval [CI], 2.00-3.56; women: OR, 3.42; 95% CI, 2.64-4.43), hypertriglyceridemia (men: OR, 1.44; 95% CI, 1.08-1.93; women: OR, 1.82; 95% CI, 1.45-2.29), and high fasting blood glucose (men: OR, 1.41; 95% CI, 1.07-1.87; women: OR, 2.03; 95% CI, 1.48-2.79).

Conclusion

Protein intake (<0.8 g protein/kg body weight/day) lower than the recommend level was associated with a higher risk of metabolic abnormalities in Korean older adults. In particular, lower intake of protein contributed to a higher prevalence of metabolic risk factors in women than in men.

Understanding Age-Related Changes in Skeletal Muscle Metabolism: Differences Between Females and Males

Skeletal muscle is the largest metabolic organ system in the human body. As such, metabolic dysfunction occurring in skeletal muscle impacts whole-body nutrient homeostasis. Macronutrient metabolism changes within the skeletal muscle with aging, and these changes are associated in part with age-related skeletal muscle remodeling. Moreover, age-related changes in skeletal muscle metabolism are affected differentially between males and females and are likely driven by changes in sex hormones. Intrinsic and extrinsic factors impact observed age-related changes and sex-related differences in skeletal muscle metabolism. Despite some support for sex-specific differences in skeletal muscle metabolism with aging, more research is necessary to identify underlying differences in mechanisms. Understanding sex-specific aging skeletal muscle will assist with the development of therapies to attenuate adverse metabolic and functional outcomes.

Protein and exercise in the prevention of sarcopenia and aging

Aging is associated with a progressive decline in skeletal muscle mass and strength. The decline, known as sarcopenia, could lead to physical disability, poor quality of life, and death. In addition, the older population usually experiences age-related muscle changes that affect muscle mass, muscular strength, and functional abilities. The purpose of this review is to describe the role of protein and exercise in slowing the progression of sarcopenia. It will also discuss whether age-related changes can be attenuated by dietary protein and exercise in the older population. This review will also cover one of the possible mechanisms of how dietary protein and exercise are involved in sarcopenia prevention, as well as the available measurement tools. Based on the findings of this review, the adequate amount of protein required for older men and women needs to be revised and likely be higher. Moreover, studies are required to explore some inconclusive findings concerning sarcopenia in the older population. Further research is required to investigate the following: (1) the safety and effectiveness concerning the consumption of 1.4 g of protein/kg of body weight (or more) in this vulnerable population; (2) the effectiveness of amino acid supplementation in reducing progression of sarcopenia over time through longitudinal studies; (3) the preferred source and timing of protein for the older population to maintain muscular strength and attenuate sarcopenia; (4) exercise interventions, especially those of longer duration, in the attenuation of sarcopenia; (5) other types of exercise and their effects on age-related muscle changes; (6) the mechanism of how protein and exercise prevent muscle loss with aging; and (7) determine the best method to diagnose sarcopenia.

Promoting Perioperative Metabolic and Nutritional Care

Surgery represents a major stressor that disrupts homeostasis and can lead to loss of body cell mass. Integrated, multidisciplinary medical strategies, including enhanced recovery programs and perioperative nutrition support, can mitigate the surgically induced metabolic response, promoting optimal patient recovery following major surgery. Clinical therapies should identify those who are poorly nourished before surgery and aim to attenuate catabolism while preserving the processes that promote recovery and immunoprotection after surgery. This review will address the impact of surgery on intermediary metabolism and describe the clinical consequences that ensue. It will also focus on the role of perioperative nutrition, including preoperative nutrition risk, carbohydrate loading, and early initiation of oral feeding (centered on macronutrients) in modulating surgical stress, as well as highlight the contribution of the anesthesiologist to nutritional care. Emerging therapeutic concepts such as preoperative glycemic control and prehabilitation will be discussed.

Frailty and nutrition: searching for evidence

Frailty is a geriatric syndrome that predicts disability, morbidity and mortality in the elderly. Poor nutritional status is one of the main risk factors for frailty. Macronutrients and micronutrients deficiencies are associated with frailty. Recent studies suggest that improving nutritional status for macronutrients and micronutrients may reduce the risk of frailty. Specific diets such as the Mediterranean diet rich in anti-oxidants, is currently investigated in the prevention of frailty. The aim of this paper is to summarize the current body of knowledge on the relations between nutrition and frailty, and provide recommendations for future nutritional research on the field of frailty.

Dietary protein intake in elderly women: association with muscle and bone mass

BACKGROUND

An inadequate food intake, mainly with regard to protein intake, seems to contribute to a reduction of skeletal muscle and bone mass in the elderly. This study was undertaken to evaluate differences in protein intake in women with or without sarcopenia and verify the intake level that is related to a better bone and muscle mass.

METHODS

Elderly women older than 65 years with sarcopenia (n = 35) and without sarcopenia (n = 165) participated in the study. Assessment of bone mineral density of the lumbar spine and femur was taken, body composition was evaluated by dual-energy x-ray absorptiometry, and an evaluation of protein intake was performed through 3-day dietary records.

RESULTS

Muscle, bone, and fat mass was significantly higher in women who had protein intake >1.2 g/kg/d. A lower intake of essential amino acids in women with sarcopenia was also observed. Protein and energy intake were significant predictors of muscle mass. The presence of osteoporosis was a predictor of muscle strength. In conclusion, the present study demonstrated that in elderly women, an adequate protein intake in terms of quality and quantity, without need of supplementation, could have a positive impact on bone mineral density, lean mass, and skeletal muscle mass.

Community-based intervention to improve dietary habits and promote physical activity among older adults: a cluster randomized trial

Background

The fastest growing age group globally is older adults, and preventing the need for long-term nursing care in this group is important for social and financial reasons. A population approach to diet and physical activity through the use of social services can play an important role in prevention. This study examined the effectiveness of a social health program for community-dwelling older adults aimed at introducing and promoting physical activity in the home at each individual’s pace, helping participants maintain good dietary habits by keeping self-check sheets, and determining whether long-standing unhealthy or less-than-ideal physical and dietary habits can be changed.

Method

This cluster randomized trial conducted at 6 community centers in an urban community involved 92 community-dwelling older adults aged 65–90 years. The intervention group (3 community centers; n = 57) participated in the social health program “Sumida TAKE10!” which is an educational program incorporating the “TAKE10!® for Older Adults” program, once every 2 weeks for 3 months. The control group (3 community centers; n=35) was subsequently provided with the same program as a crossover intervention group. The main outcome measures were changes in food intake frequency, food frequency score (FFS), dietary variety score (DVS), and frequency of walking and exercise. The secondary outcome measures were changes in self-rated health, appetite, and the Tokyo Metropolitan Institute of Gerontology (TMIG) Index of Competence score.

Results

Compared to baseline, post-intervention food intake frequency for 6 of 10 food groups (meat, fish/shellfish, eggs, potatoes, fruits, and seaweed), FFS, and DVS were significantly increased in the intervention group, and interaction effects of FFS and DVS were seen between the two groups. No significant differences were observed between baseline and post-intervention in the control group. Frequency of walking and exercise remained unchanged in both groups, and no significant difference in improvement rate was seen between the groups. Self-rated health was significantly increased in the intervention group. Appetite and TMIG Index of Competence score were unchanged in both groups.

Conclusions

The social health program resulted in improved dietary habits, as measured by food intake frequency, FFS, and DVS, and may improve self-rated health among community-dwelling older adults.

Trial registration number

UMIN000007357

Distributional fold change test - a statistical approach for detecting differential expression in microarray experiments

Background

Because of the large volume of data and the intrinsic variation of data intensity observed in microarray experiments, different statistical methods have been used to systematically extract biological information and to quantify the associated uncertainty. The simplest method to identify differentially expressed genes is to evaluate the ratio of average intensities in two different conditions and consider all genes that differ by more than an arbitrary cut-off value to be differentially expressed. This filtering approach is not a statistical test and there is no associated value that can indicate the level of confidence in the designation of genes as differentially expressed or not differentially expressed. At the same time the fold change by itself provide valuable information and it is important to find unambiguous ways of using this information in expression data treatment.

Results

A new method of finding differentially expressed genes, called distributional fold change (DFC) test is introduced. The method is based on an analysis of the intensity distribution of all microarray probe sets mapped to a three dimensional feature space composed of average expression level, average difference of gene expression and total variance. The proposed method allows one to rank each feature based on the signal-to-noise ratio and to ascertain for each feature the confidence level and power for being differentially expressed. The performance of the new method was evaluated using the total and partial area under receiver operating curves and tested on 11 data sets from Gene Omnibus Database with independently verified differentially expressed genes and compared with the t-test and shrinkage t-test. Overall the DFC test performed the best – on average it had higher sensitivity and partial AUC and its elevation was most prominent in the low range of differentially expressed features, typical for formalin-fixed paraffin-embedded sample sets.

Conclusions

The distributional fold change test is an effective method for finding and ranking differentially expressed probesets on microarrays. The application of this test is advantageous to data sets using formalin-fixed paraffin-embedded samples or other systems where degradation effects diminish the applicability of correlation adjusted methods to the whole feature set.

Lifestyle and sarcopenia-etiology, prevention, and treatment

The term sarcopenia describes the loss of skeletal muscle mass, strength, and function in old age. As the world population continues to grow older, more attention is given to the phenomena of sarcopenia and the search for strategies of prevention and treatment. The progression of sarcopenia is affected by age-related physiological and systemic changes in the body, including alterations in skeletal muscle tissue, hormonal changes, increased inflammatory activities, and oxidative stress. Sarcopenia progression is also affected by lifestyle factors which are far more controllable. These factors include various aspects of nutrition, physical activity, exercise, alcohol intake, and tobacco use. Raising the public awareness regarding the impact of these factors, as causes of sarcopenia and potential strategies of prevention and treatment, is of great importance. In this review we aim to describe various lifestyle factors that affect the etiology, prevention, and treatment of sarcopenia.

Myogenic mRNA markers in young and old human skeletal muscle prior to and following sequential exercise bouts

This study examined how multiple bouts of conventional resistance training affected the mRNA expression of transcripts and a protein associated with satellite cell activity in human skeletal muscle. Ten younger men (means ± SE; age, 21.0 ± 0.5 years; body mass, 82.3 ± 4.2 kg; height, 178.4 ± 2.2 cm; percent body fat, 15.4% ± 2.9%) and 10 older men (age, 66.4 ± 1.6 years; body mass, 94.2 ± 3.7 kg; height, 180.9 ± 2.2 cm; percent body fat, 27.4% ± 1.8%) completed 3 lower-body workouts (Monday, Wednesday, Friday; 9 sets of 10 repetitions at 80% 1 repetition maximum). Vastus lateralis muscle biopsies were collected prior to intervention (T1), 48 h following workout 1 (T2), 48 h following workout 2 (T3), and 24 h following workout 3 (T4). Real-time reverse transcription-polymerase chain reaction was performed to assess genes of interest, and muscle proliferating cell nuclear antigen (PCNA) was assessed using Western blotting. The CYCLIN D1 gene was expressed more highly in the older vs. younger men (p < 0.05), whereas the expression of all other genes and muscle PCNA were similar between age groups. MYOD mRNA expression increased at T2 (p < 0.05) and MHCEMB gene expression modestly increased (p < 0.05) at T4 relative to baseline expression values in the younger men. Baseline elevations in CYCLIN D1 mRNA expression in older persons may indicate that a compensatory expression of this transcript is occurring in an attempt to retain the muscle's proliferative potential. Increases in MYOD and MHCEMB indicate that 1 week of conventional resistance exercise may i crease myogenic activity, including satellite cell proliferation and differentiation, respectively, in younger men.

Global gene expression profiles in skeletal muscle of monozygotic female twins discordant for hormone replacement therapy

Aging is accompanied by inexorable loss of muscle tissue. One of the underlying causes for this is the massive change in the hormonal milieu of the body. The role of a female sex steroid - estrogen - in these processes is frequently neglected, although the rapid decline in its production coincides with a steep deterioration in muscle performance. We recruited 54- to 62-year-old monozygotic female twin pairs discordant for postmenopausal hormone replacement therapy (HRT, n=11 pairs; HRT use 7.3 ± 3.7 years) from the Finnish Twin Cohort to investigate the association of long-term, estrogen-based HRT with skeletal muscle transcriptome. Pathway analysis of muscle transcript profiles revealed significant HRT-induced up-regulation of a biological process related to regulation of cell structure and down-regulation of processes concerning, for example, cell-matrix interactions, energy metabolism and utilization of nutrients (false discovery rate < 0.15). Lending clinical relevance to the findings, these processes explained a significant fraction of the differences observed in relative proportion of muscle within thigh and in muscle performance (R(2) =0.180-0.257, P=0.001-0.023). Although energy metabolism was affected through down-regulation of the transcripts related to succinate dehydrogenase complex in mitochondria, no differences were observed in mtDNA copy number or oxidative capacity per muscle cross section. In conclusion, long-term use of HRT was associated with subtle, but significant, differences in muscle transcript profiles. The better muscle composition and performance among the HRT users appeared to be orchestrated by improved regulatory actions on cytoskeleton, preservation of muscle quality via regulation of intramuscular extracellular matrix and a switch from glucose-oriented metabolism to utilization of fatty acids.

Effect of protein intake on bone and muscle mass in the elderly

The aging process is frequently characterized by an involuntary loss of muscle (sarcopenia) and bone (osteoporosis) mass. Both chronic diseases are associated with decreased metabolic rate, increased risk of falls/fracture, and, as a result, increased morbidity and loss of independence in the elderly. The quality and quantity of protein intake affects bone and muscle mass in several ways and there is evidence that increased essential amino acid or protein availability can enhance muscle protein synthesis and anabolism, as well as improve bone homeostasis in older subjects. A thorough evaluation of renal function is important, since renal function decreases with age. Finally, protein and calcium intake should be considered in the prevention or treatment of the chronic diseases osteoporosis and sarcopenia.

The skeletal muscle transcript profile reflects accommodative responses to inadequate protein intake in younger and older males

Inadequate protein intake initiates adverse changes in skeletal muscle function and structure (i.e., an accommodative response). mRNA level changes due to short-term inadequate dietary protein might be an early indication of subsequent accommodation. The aims of this study were to assess the effects of dietary protein and the diet-by-age interaction on the skeletal muscle transcriptome. Twelve younger (21-43 y) and 10 older (63-79 y) men completed three controlled feeding trials with protein intakes of 0.50 (LPro: lower protein), 0.75 (MPro: medium protein) and 1.00 g protein·kg body weight⁻¹·day⁻¹ (HPro: higher protein). A fasting state biopsy was taken on Day 12 of each trial. Global changes in transcript levels were assessed with Affymetrix genechips and expression patterns determined using self-organizing maps. Nine hundred fifty-eight transcripts were differentially expressed (P<.05) by diet and 853 had a diet-by-age interaction (P<.05). The results for diet alone revealed that LPro was associated with up-regulation of transcripts related to ubiquitin-dependent protein catabolism and muscle contraction and LPro and MPro resulted in up-regulation of transcripts related to apoptosis and down-regulation of transcripts related to cell differentiation, muscle and organ development, extracellular space and responses to stimuli and stress. The diet-by-age effect on protein modification transcripts was consistent with the older males being less responsive to anabolic stimuli (lower protein synthesis at HPro) and more responsive to a catabolic state (protein breakdown at LPro). Changes in skeletal muscle mRNA levels in younger and older males to protein intake near or below the recommended dietary allowance are indicative of an early accommodative response.

Power training and postmenopausal hormone therapy affect transcriptional control of specific co-regulated gene clusters in skeletal muscle

At the moment, there is no clear molecular explanation for the steeper decline in muscle performance after menopause or the mechanisms of counteractive treatments. The goal of this genome-wide study was to identify the genes and gene clusters through which power training (PT) comprising jumping activities or estrogen containing hormone replacement therapy (HRT) may affect skeletal muscle properties after menopause. We used musculus vastus lateralis samples from early stage postmenopausal (50-57 years old) women participating in a yearlong randomized double-blind placebo-controlled trial with PT and HRT interventions. Using microarray platform with over 24,000 probes, we identified 665 differentially expressed genes. The hierarchical clustering method was used to assort the genes. Additionally, enrichment analysis of gene ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways was carried out to clarify whether assorted gene clusters are enriched with particular functional categories. The analysis revealed transcriptional regulation of 49 GO/KEGG categories. PT upregulated transcription in "response to contraction"-category revealing novel candidate genes for contraction-related regulation of muscle function while HRT upregulated gene expression related to functionality of mitochondria. Moreover, several functional categories tightly related to muscle energy metabolism, development, and function were affected regardless of the treatment. Our results emphasize that during the early stages of the postmenopause, muscle properties are under transcriptional modulation, which both PT and HRT partially counteract leading to preservation of muscle power and potentially reducing the risk for aging-related muscle weakness. More specifically, PT and HRT may function through improving energy metabolism, response to contraction as well as by preserving functionality of the mitochondria.

Effect of protein/essential amino acids and resistance training on skeletal muscle hypertrophy: A case for whey protein

Regardless of age or gender, resistance training or provision of adequate amounts of dietary protein (PRO) or essential amino acids (EAA) can increase muscle protein synthesis (MPS) in healthy adults. Combined PRO or EAA ingestion proximal to resistance training, however, can augment the post-exercise MPS response and has been shown to elicit a greater anabolic effect than exercise plus carbohydrate. Unfortunately, chronic/adaptive response data comparing the effects of different protein sources is limited. A growing body of evidence does, however, suggest that dairy PRO, and whey in particular may: 1) stimulate the greatest rise in MPS, 2) result in greater muscle cross-sectional area when combined with chronic resistance training, and 3) at least in younger individuals, enhance exercise recovery. Therefore, this review will focus on whey protein supplementation and its effects on skeletal muscle mass when combined with heavy resistance training.

Dairy proteins and the response to pneumovax in senior citizens: a randomized, double-blind, placebo-controlled pilot study

With the progressive aging of the world's population, immunosenescence is rapidly becoming a clinical concern as it accounts for a higher incidence of severe infections and poor response to vaccines. To identify nutritional approaches that may counteract immunosenescence is of obvious importance in clinical practice. Dairy products in general and whey proteins in particular share the capacity to stimulate the immune system within the digestive tract while the antibody response to Streptococcus pneumoniae vaccine is a good marker of the immune function. We performed a controlled, randomized, double-blind pilot study to determine if an eight-week supplementation with whey protein (or soy protein used as control) could enhance the serum response to pneumococcal vaccine in healthy senior citizens. Out of 127 volunteers, 17 subjects were eligible and completed the study receiving the vaccine after four weeks of supplementation. Antibody levels were measured at baseline and the end of the study against 14 pneumococcal types and a detailed nutritional questionnaire was administered to all subjects. Subjects receiving whey protein manifested a serum response higher compared to the control soy supplementation against 12/14 bacterial types. In particular, whey led to a higher frequency of response to all four more virulent types (4, 9, 14, and 23). Calorie and protein intake data suggest a better nutritional status in the whey group. Whey protein supplementation is a promising supplement to stimulate the immune response to vaccine in senior citizens and possibly to counteract immunosenescence while larger studies are warranted.

Evidence that protein requirements have been significantly underestimated

PURPOSE OF REVIEW

This review discusses recent evidence that suggests a significant underestimation of protein requirements in adult humans.

RECENT FINDINGS

Traditionally, total protein requirements for humans have been determined using nitrogen balance. The recent Dietary Reference Intake recommendations for mean and population-safe intakes of 0.66 and 0.8 g/kg/day, respectively, of high-quality protein in adult humans are based on a meta-analysis of nitrogen balance studies using single linear regression analysis. We reanalyzed existing nitrogen balance studies using two-phase linear regression analysis and obtained mean and safe protein requirements of 0.91 and 0.99 g/kg/day, respectively. The two-phase linear regression analysis is considered more appropriate for biological analysis of dose-response curves. Considering the inherent problems associated with the nitrogen balance method, we developed an alternative method, the indicator amino acid oxidation technique, to determine protein requirements The mean and population-safe requirements in adult men were determined to be 0.93 and 1.2 g/kg/day and are 41 and 50%, respectively, higher than the current Dietary Reference Intakes recommendations.

SUMMARY

The indicator amino acid oxidation-based requirement values of 0.93 and 1.2 g protein/kg/day and the reanalysis of existing nitrogen balance studies are significantly higher than current recommendations. Therefore, there is an urgent need to reassess recommendations for protein intake in adult humans.

Does habitual dietary intake influence myofiber hypertrophy in response to resistance training? A cluster analysis

Although resistance exercise training (RT) is a common intervention to stimulate muscle protein synthesis and increase skeletal muscle mass, the optimal daily protein and total energy intakes sufficient to support RT-mediated muscle growth are as yet unclear. Further, the efficacy of RT varies widely among adults of all ages and whether this is attributable to interindividual differences in nutrition is not known. To determine if self-selected daily intake of macronutrients and specific components of dietary protein and fat are predictive of the magnitude of RT-mediated muscle growth, detailed 4-day dietary records were analyzed on 60 subjects previously clustered (K-means cluster analysis) as non-, modest, and extreme responders (non, n = 16; mod, n = 29; xtr, n = 15), based on the magnitudes of change in vastus lateralis myofiber cross-sectional area following a 16-week, 3-day-per-week, high-intensity RT. Despite the marked contrast between 60% myofiber hypertrophy in xtr and zero growth in non, we found no differences among response clusters in daily intakes of energy (mean +/- SEM: non 102 +/- 8; mod 111 +/- 6; xtr 109 +/- 5 kJ.kg-1.day-1), protein (non 0.97 +/- 0.08; mod 1.07 +/- 0.07; xtr 1.05 +/- 0.06 g.kg-1.day-1), carbohydrate (non 3.02 +/- 0.24; mod 3.18 +/- 0.20; xtr 3.14 +/- 0.17 g.kg-1.day-1), and fat (non 0.95 +/- 0.09; mod 1.05 +/- 0.08; xtr 1.03 +/- 0.08 g.kg-1.day-1), which generally met or exceeded dietary recommendations. There were no cluster differences in intakes of branched chain amino acids known to stimulate muscle protein synthesis. Using the novel K-means clustering approach, we conclude from this preliminary study that protein and energy intakes were sufficient to facilitate modest and extreme muscle growth during RT and intrinsic or extrinsic factors other than nutrient ingestion apparently impaired the anabolic response in nonresponders.

Dietary protein recommendations and the prevention of sarcopenia

PURPOSE OF REVIEW

To draw attention to recent work on the role of protein and the amount of protein needed with each meal to preserve skeletal muscle mass in ageing.

RECENT FINDINGS

Ageing does not inevitably reduce the anabolic response to a high-quality protein meal. Ingestion of approximately 25-30 g of protein per meal maximally stimulates muscle protein synthesis in both young and older individuals. However, muscle protein synthesis is blunted in elderly when protein and carbohydrate are coingested or when the quantity of protein is less than approximately 20 g per meal. Supplementing regular mixed-nutrient meals with leucine may also enhance the muscle protein synthetic response in elders.

SUMMARY

On the basis of recent work, we propose a novel and specific dietary approach to prevent or slow down muscle loss with ageing. Rather than recommending a large, global increase in the recommended dietary allowance (RDA) for protein for all elderly individuals, clinicians should stress the importance of ingesting a sufficient amount of protein with each meal. To maximize muscle protein synthesis while being cognizant of total energy intake, we propose a dietary plan that includes 25-30 g of high quality protein per meal.

Nutritional consideration in the aging athlete

OBJECTIVE

: To evaluate the evidence for dietary recommendations in older adult athletes.

DESIGN

: Interpretive review of the literature.

RESULTS

: Regarding resistance training, a protein intake of slightly more than 0.8 g/kg/d is required to optimize gains in muscle strength. The early provision of protein and carbohydrate following a weight training session can enhance resultant strength and fat-free mass gains. Supplementation with creatine monohydrate (approximately 5 g/d) can potentiate some of the gains in strength and fat free mass attained through resistance exercise training. Regarding endurance exercise training, there are no studies evaluating carbohydrate loading, during-event, or postexercise carbohydrate/nutritional replacement in older adults.

CONCLUSIONS

: The amount and timing of dietary protein is important to maximize strength and gains in fat-free mass during resistance exercise training. Creatine monohydrate supplementation can potentiate some of these gains during the first 4 to 6 months of training. Older adults should consume adequate carbohydrates during endurance training (6-8 g/kg/d) and may benefit from the provision of carbohydrate and protein in the early recovery phase following endurance exercise to maximize glycogen re-synthesis for a subsequent exercise bout. There is no scientific reason to assume that older athletes will respond differently to the pre- and during-race fluid and carbohydrate replacement strategies suggested for younger athletes. The consensus guidelines outlined by the American College of Sports Medicine should therefore be followed for all athletes, regardless of their age.

Acute and long-term effects of resistance exercise with or without protein ingestion on muscle hypertrophy and gene expression

The effects of timed ingestion of high-quality protein before and after resistance exercise are not well known. In this study, young men were randomized to protein (n = 11), placebo (n = 10) and control (n = 10) groups. Muscle cross-sectional area by MRI and muscle forces were analyzed before and after 21 weeks of either heavy resistance training (RT) or control period. Muscle biopsies were taken before, and 1 and 48 h after 5 x 10 repetition leg press exercise (RE) as well as 21 weeks after RT. Protein (15 g of whey both before and after exercise) or non-energetic placebo were provided to subjects in the context of both single RE bout (acute responses) as well as each RE workout twice a week throughout the 21-week-RT. Protein intake increased (P < or = 0.05) RT-induced muscle cross-sectional area enlargement and cell-cycle kinase cdk2 mRNA expression in the vastus lateralis muscle suggesting higher proliferating cell activation response with protein supplementation. Moreover, protein intake seemed to prevent 1 h post-RE decrease in myostatin and myogenin mRNA expression but did not affect activin receptor IIb, p21, FLRG, MAFbx or MyoD expression. In conclusion, protein intake close to resistance exercise workout may alter mRNA expression in a manner advantageous for muscle hypertrophy.

A weighted average difference method for detecting differentially expressed genes from microarray data

Background

Identification of differentially expressed genes (DEGs) under different experimental conditions is an important task in many microarray studies. However, choosing which method to use for a particular application is problematic because its performance depends on the evaluation metric, the dataset, and so on. In addition, when using the Affymetrix GeneChip^® system, researchers must select a preprocessing algorithm from a number of competing algorithms such as MAS, RMA, and DFW, for obtaining expression-level measurements. To achieve optimal performance for detecting DEGs, a suitable combination of gene selection method and preprocessing algorithm needs to be selected for a given probe-level dataset.

Results

We introduce a new fold-change (FC)-based method, the weighted average difference method (WAD), for ranking DEGs. It uses the average difference and relative average signal intensity so that highly expressed genes are highly ranked on the average for the different conditions. The idea is based on our observation that known or potential marker genes (or proteins) tend to have high expression levels. We compared WAD with seven other methods; average difference (AD), FC, rank products (RP), moderated t statistic (modT), significance analysis of microarrays (samT), shrinkage t statistic (shrinkT), and intensity-based moderated t statistic (ibmT). The evaluation was performed using a total of 38 different binary (two-class) probe-level datasets: two artificial "spike-in" datasets and 36 real experimental datasets. The results indicate that WAD outperforms the other methods when sensitivity and specificity are considered simultaneously: the area under the receiver operating characteristic curve for WAD was the highest on average for the 38 datasets. The gene ranking for WAD was also the most consistent when subsets of top-ranked genes produced from three different preprocessed data (MAS, RMA, and DFW) were compared. Overall, WAD performed the best for MAS-preprocessed data and the FC-based methods (AD, WAD, FC, or RP) performed well for RMA and DFW-preprocessed data.

Conclusion

WAD is a promising alternative to existing methods for ranking DEGs with two classes. Its high performance should increase researchers' confidence in microarray analyses.

Amino acid metabolism and regulatory effects in aging

PURPOSE OF REVIEW

To examine recent discoveries related to the amino acid metabolism and regulatory effects in aging, focusing on the development and treatment of age-related muscle loss (sarcopenia).

RECENT FINDINGS

While basal amino acid metabolism may be unaffected by age, elderly subjects appear to have a decreased ability to respond to anabolic stimuli such as insulin and, to a lesser extent, amino acids. Specifically, compared to young subjects, the stimulation of muscle protein synthesis is attenuated in elderly subjects following the administration of mixed meals due to insulin resistance. In addition, the anabolic effect of amino acids appears blunted at low doses. Recent studies, however, have highlighted that these age-related alterations in amino acid metabolism may be overcome by provision of excess leucine, changes in the daily protein intake pattern or exercise, which improve activation of translation initiation and muscle protein synthesis.

SUMMARY

Muscle loss with aging is associated with significant changes in amino acid metabolism, which can be acutely reversed using nutritional manipulations and exercise. Long-term, large clinical trials are, however, needed to determine the clinical significance of these findings in the elderly population, and to establish if nutritional and exercise interventions can help prevent and treat sarcopenia.

The effects of whey protein on myostatin and cell cycle-related gene expression responses to a single heavy resistance exercise bout in trained older men

Myostatin decreases muscle mass and this is accomplished, in part, by inhibiting muscle satellite cell proliferation and differentiation by regulating the expression of cell cycle-related proteins (e.g. p21 and cdk2) and myogenic regulatory factors (e.g. myogenin and MyoD). The purpose of this investigation was to determine whether protein ingestion before and after a resistance exercise (RE) bout affects myostatin and cell cycle-related gene expression. Strength-trained middle-aged to older men were divided into a protein group (61.4 +/- 4.3 years, n = 9) or a placebo group (62.1 +/- 4.2 years, n = 9). Muscle biopsies from the vastus lateralis muscle were taken at rest and 1 and 48 h after a 5 x 10 repetition leg press RE bout. Protein (15 g whey) or non-caloric placebo was taken immediately before and after the RE bout. mRNA expression levels of myostatin and related genes (AcvrIIb, FLRG, p21, p27, cdk2, myogenin and MyoD) were determined by Taqman probe-based real-time RT-PCR and normalized to GAPDH mRNA. Myostatin mRNA decreased after a RE bout, but only in the placebo group (P < or = 0.05). Conversely, myostatin-binding protein FLRG and cell-cycle kinase cdk2 mRNA increased only in the protein group (P < or = 0.05). p21 mRNA was increased at 1 h post-RE in placebo (P < or = 0.05) and tended to be increased in the protein group (P = 0.08). Myostatin, its binding protein and cell cycle-related gene expressions are affected by single RE bout and these responses are further modified by whey protein intake. Therefore, controlling nutrition intake is important when studying gene expression responses to exercise.