Increased Protein Intake Reduces Lean Body Mass Loss during Weight Loss in Athletes

A brief review of critical processes in exercise-induced muscular hypertrophy

With regular practice, resistance exercise can lead to gains in skeletal muscle mass by means of hypertrophy. The process of skeletal muscle fiber hypertrophy comes about as a result of the confluence of positive muscle protein balance and satellite cell addition to muscle fibers. Positive muscle protein balance is achieved when the rate of new muscle protein synthesis (MPS) exceeds that of muscle protein breakdown (MPB). While resistance exercise and postprandial hyperaminoacidemia both stimulate MPS, it is through the synergistic effects of these two stimuli that a net gain in muscle proteins occurs and muscle fiber hypertrophy takes place. Current evidence favors the post-exercise period as a time when rapid hyperaminoacidemia promotes a marked rise in the rate of MPS. Dietary proteins with a full complement of essential amino acids and high leucine contents that are rapidly digested are more likely to be efficacious in this regard. Various other compounds have been added to complete proteins, including carbohydrate, arginine and glutamine, in an attempt to augment the effectiveness of the protein in stimulating MPS (or suppressing MPB), but none has proved particularly effective. Evidence points to a higher protein intake in combination with resistance exercise as being efficacious in allowing preservation, and on occasion increases, in skeletal muscle mass with dietary energy restriction aimed at the promotion of weight loss. The goal of this review is to examine practices of protein ingestion in combination with resistance exercise that have some evidence for efficacy and to highlight future areas for investigation.

A high-protein diet for reducing body fat: mechanisms and possible caveats

High protein diets are increasingly popularized in lay media as a promising strategy for weight loss by providing the twin benefits of improving satiety and decreasing fat mass. Some of the potential mechanisms that account for weight loss associated with high-protein diets involve increased secretion of satiety hormones (GIP, GLP-1), reduced orexigenic hormone secretion (ghrelin), the increased thermic effect of food and protein-induced alterations in gluconeogenesis to improve glucose homeostasis. There are, however, also possible caveats that have to be considered when choosing to consume a high-protein diet. A high intake of branched-chain amino acids in combination with a western diet might exacerbate the development of metabolic disease. A diet high in protein can also pose a significant acid load to the kidneys. Finally, when energy demand is low, excess protein can be converted to glucose (via gluconeogenesis) or ketone bodies and contribute to a positive energy balance, which is undesirable if weight loss is the goal. In this review, we will therefore explore the mechanisms whereby a high-protein diet may exert beneficial effects on whole body metabolism while we also want to present possible caveats associated with the consumption of a high-protein diet.

Nutritional strategies to support concurrent training

Concurrent training (the combination of endurance exercise to resistance training) is a common practice for athletes looking to maximise strength and endurance. Over 20 years ago, it was first observed that performing endurance exercise after resistance exercise could have detrimental effects on strength gains. At the cellular level, specific protein candidates have been suggested to mediate this training interference; however, at present, the physiological reason(s) behind the concurrent training effect remain largely unknown. Even less is known regarding the optimal nutritional strategies to support concurrent training and whether unique nutritional approaches are needed to support endurance and resistance exercise during concurrent training approaches. In this review, we will discuss the importance of protein supplementation for both endurance and resistance training adaptation and highlight additional nutritional strategies that may support concurrent training. Finally, we will attempt to synergise current understanding of the interaction between physiological responses and nutritional approaches into practical recommendations for concurrent training.

Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation

The popularity of natural bodybuilding is increasing; however, evidence-based recommendations for it are lacking. This paper reviewed the scientific literature relevant to competition preparation on nutrition and supplementation, resulting in the following recommendations. Caloric intake should be set at a level that results in bodyweight losses of approximately 0.5 to 1%/wk to maximize muscle retention. Within this caloric intake, most but not all bodybuilders will respond best to consuming 2.3-3.1 g/kg of lean body mass per day of protein, 15-30% of calories from fat, and the reminder of calories from carbohydrate. Eating three to six meals per day with a meal containing 0.4-0.5 g/kg bodyweight of protein prior and subsequent to resistance training likely maximizes any theoretical benefits of nutrient timing and frequency. However, alterations in nutrient timing and frequency appear to have little effect on fat loss or lean mass retention. Among popular supplements, creatine monohydrate, caffeine and beta-alanine appear to have beneficial effects relevant to contest preparation, however others do not or warrant further study. The practice of dehydration and electrolyte manipulation in the final days and hours prior to competition can be dangerous, and may not improve appearance. Increasing carbohydrate intake at the end of preparation has a theoretical rationale to improve appearance, however it is understudied. Thus, if carbohydrate loading is pursued it should be practiced prior to competition and its benefit assessed individually. Finally, competitors should be aware of the increased risk of developing eating and body image disorders in aesthetic sport and therefore should have access to the appropriate mental health professionals.

Reduced resting skeletal muscle protein synthesis is rescued by resistance exercise and protein ingestion following short-term energy deficit

The myofibrillar protein synthesis (MPS) response to resistance exercise (REX) and protein ingestion during energy deficit (ED) is unknown. In young men (n = 8) and women (n = 7), we determined protein signaling and resting postabsorptive MPS during energy balance [EB; 45 kcal·kg fat-free mass (FFM)(-1)·day(-1)] and after 5 days of ED (30 kcal·kg FFM(-1)·day(-1)) as well as MPS while in ED after acute REX in the fasted state and with the ingestion of whey protein (15 and 30 g). Postabsorptive rates of MPS were 27% lower in ED than EB (P < 0.001), but REX stimulated MPS to rates equal to EB. Ingestion of 15 and 30 g of protein after REX in ED increased MPS ~16 and ~34% above resting EB (P < 0.02). p70 S6K Thr(389) phosphorylation increased above EB only with combined exercise and protein intake (~2-7 fold, P < 0.05). In conclusion, short-term ED reduces postabsorptive MPS; however, a bout of REX in ED restores MPS to values observed at rest in EB. The ingestion of protein after REX further increases MPS above resting EB in a dose-dependent manner. We conclude that combining REX with increased protein availability after exercise enhances rates of skeletal muscle protein synthesis during short-term ED and could in the long term preserve muscle mass.

Effect of leucine supplementation on fat free mass with prolonged hypoxic exposure during a 13-day trek to Everest Base Camp: a double-blind randomized study

Loss of body weight and fat-free mass (FFM) are commonly noted with prolonged exposure to hypobaric hypoxia. Recent evidence suggests protein supplementation, specifically leucine, may potentially attenuate loss of FFM in subcaloric conditions during normoxia. The purpose of this study was to determine if leucine supplementation would prevent the loss of FFM in subcaloric conditions during prolonged hypoxia. Eighteen physically active male (n = 10) and female (n = 8) trekkers completed a 13-day trek in Nepal to Everest Base Camp with a mean altitude of 4140 m (range 2810–5364 m). In this double-blind study, participants were randomized to ingest either leucine (LEU) (7 g leucine, 93 kcal, 14.5 g whey-based protein) or an isocaloric isonitrogenous control (CON) (0.3 g LEU, 93 kcal, 11.3 g collagen protein) twice daily prior to meals. Body weight, body composition, and circumferences of bicep, thigh, and calf were measured pre- and post-trek. There was a significant time effect for body weight (−2.2% ± 1.7%), FFM (−1.7% ± 1.5%), fat mass (−4.0% ± 6.9%), and circumferences (p < 0.05). However, there was no treatment effect on body weight (CON −2.3 ± 2.0%; LEU −2.2 ± 1.5%), FFM (CON −2.1 ± 1.5%; LEU −1.2 ± 1.6%), fat mass (CON −2.9% ± 5.9%; LEU −5.4% ± 8.1%), or circumferences. Although a significant loss of body weight, FFM, and fat mass was noted in 13 days of high altitude exposure, FFM loss was not attenuated by leucine. Future studies are needed to determine if leucine attenuates loss of FFM with longer duration high altitude exposure.

Metabolic adaptation to weight loss: implications for the athlete

Optimized body composition provides a competitive advantage in a variety of sports. Weight reduction is common among athletes aiming to improve their strength-to-mass ratio, locomotive efficiency, or aesthetic appearance. Energy restriction is accompanied by changes in circulating hormones, mitochondrial efficiency, and energy expenditure that serve to minimize the energy deficit, attenuate weight loss, and promote weight regain. The current article reviews the metabolic adaptations observed with weight reduction and provides recommendations for successful weight reduction and long term reduced-weight maintenance in athletes.

Nutritional strategies for the preservation of fat free mass at high altitude

Exposure to extreme altitude presents many physiological challenges. In addition to impaired physical and cognitive function, energy imbalance invariably occurs resulting in weight loss and body composition changes. Weight loss, and in particular, loss of fat free mass, combined with the inherent risks associated with extreme environments presents potential performance, safety, and health risks for those working, recreating, or conducting military operations at extreme altitude. In this review, contributors to muscle wasting at altitude are highlighted with special emphasis on protein turnover. The article will conclude with nutritional strategies that may potentially attenuate loss of fat free mass during high altitude exposure.

Beyond muscle hypertrophy: why dietary protein is important for endurance athletes

Recovery from the demands of daily training is an essential element of a scientifically based periodized program whose twin goals are to maximize training adaptation and enhance performance. Prolonged endurance training sessions induce substantial metabolic perturbations in skeletal muscle, including the depletion of endogenous fuels and damage/disruption to muscle and body proteins. Therefore, increasing nutrient availability (i.e., carbohydrate and protein) in the post-training recovery period is important to replenish substrate stores and facilitate repair and remodelling of skeletal muscle. It is well accepted that protein ingestion following resistance-based exercise increases rates of skeletal muscle protein synthesis and potentiates gains in muscle mass and strength. To date, however, little attention has focused on the ability of dietary protein to enhance skeletal muscle remodelling and stimulate adaptations that promote an endurance phenotype. The purpose of this review is to critically discuss the results of recent studies that have examined the role of dietary protein for the endurance athlete. Our primary aim is to consider the results from contemporary investigations that have advanced our knowledge of how the manipulation of dietary protein (i.e., amount, type, and timing of ingestion) can facilitate muscle remodelling by promoting muscle protein synthesis. We focus on the role of protein in facilitating optimal recovery from, and promoting adaptations to strenuous endurance-based training.

Synergistic effects of resistance training and protein intake: practical aspects

Resistance training is a potent stimulus to increase skeletal muscle mass. The muscle protein accretion process depends on a robust synergistic action between protein intake and overload. The intake of protein after resistance training increases plasma amino acids, which results in the activation of signaling molecules leading to increased muscle protein synthesis (MPS) and muscle hypertrophy. Although both essential and non-essential amino acids are necessary for hypertrophy, the intake of free L-leucine or high-leucine whole proteins has been specifically shown to increase the initiation of translation that is essential for elevated MPS. The literature supports the use of protein intake following resistance-training sessions to enhance MPS; however, less understood are the effects of different protein sources and timing protocols on MPS. The sum of the adaptions from each individual training session is essential to muscle hypertrophy, and thus highlights the importance of an optimal supplementation protocol. The aim of this review is to present recent findings reported in the literature and to discuss the practical application of these results. In that light, new speculations and questions will arise that may direct future investigations. The information and recommendations generated in this review should be of benefit to clinical dietitians as well as those engaged in sports.

Protein supplementation in U.S. military personnel

Protein supplements (PSs) are, after multivitamins, the most frequently consumed dietary supplement by U.S. military personnel. Warfighters believe that PSs will improve health, promote muscle strength, and enhance physical performance. The estimated prevalence of regular PS use by military personnel is nearly 20% or more in active-duty personnel, which is comparable to collegiate athletes and recreationally active adults, but higher than that for average U.S. civilians. Although the acute metabolic effects of PS ingestion are well described, little is known regarding the benefits of PS use by warfighters in response to the metabolic demands of military operations. When dietary protein intake approaches 1.5 g · kg(-1) · d(-1), and energy intake matches energy expenditure, the use of PSs by most physically active military personnel may not be necessary. However, dismounted infantry often perform operations consisting of long periods of strenuous physical activity coupled with inadequate dietary energy and protein intake. In these situations, the use of PSs may have efficacy for preserving fat-free mass. This article reviews the available literature regarding the prevalence of PS use among military personnel. Furthermore, it highlights the unique metabolic stressors affecting U.S. military personnel and discusses potential conditions during which protein supplementation might be beneficial.

Increased protein intake in military special operations

Special operations are so designated for the specialized military missions they address. As a result, special operations present some unique metabolic challenges. In particular, soldiers often operate in a negative energy balance in stressful and demanding conditions with little opportunity for rest or recovery. In this framework, findings inferred from the performance literature suggest that increased protein intake may be beneficial. In particular, increased protein intake during negative caloric balance maintains lean body mass and blood glucose production. The addition of protein to mixed macronutrient supplements is beneficial for muscle endurance and power endpoints, and the use of amino acids improves gross and fine motor skills. Increasing protein intake during periods of intense training and/or metabolic demand improves subsequent performance, improves muscular recovery, and reduces symptoms of psychological stress. Consumption of protein before sleep confers the anabolic responses required for the maintenance of lean mass and muscle recovery. A maximal response in muscle protein synthesis is achieved with the consumption of 20-25 g of protein alone. However, higher protein intakes in the context of mixed-nutrient ingestion also confer anabolic benefits by reducing protein breakdown. Restricted rations issued to special operators provide less than the RDA for protein ( ∼ 0.6 g/kg), and these soldiers often rely on commercial products to augment their rations. The provision of reasonable alternatives and/or certification of approved supplements by the U.S. Department of Defense would be prudent.

Considerations for protein supplementation in warfighters

Ingestion of dietary protein stimulates the synthesis of numerous body proteins. This effect is manifest via hyperaminoacidemia with insulin as a permissive factor. In a sedentary person in energy balance, it is possible to maintain nitrogen balance while consuming protein at an intake of 0.8 g protein · kg(-1) · d(-1). What is unclear is whether being in nitrogen balance is optimal for protein synthesis and not merely adequate and representative of adaptive strategies that could lead to accommodation in "stressed" physiological states. It is clear that being in negative energy balance results in reductions in lean mass and reduced rates of protein synthesis, which can be mitigated by consumption of higher (i.e., 2-3 times the RDA) dietary protein. That long-term practice of inadequate protein intake leads to reduced metabolic, physiological, and physical function provides the basic rationale for the consumption of more than merely adequate protein to prevent not only adaptation but accommodation. Warfighters engaged in combat have been shown to have high daily physical activity energy expenditure, engage in voluntary energy restriction, and are under high metabolic and mental stress. Thus, as a group warfighters would be at risk of consuming suboptimal protein intakes and therefore may benefit from higher amounts of dietary protein intake. Balanced against the potential risk of consuming higher protein, the scientific documentation for which is lacking, there is a strong rationale for the recommendation of higher protein intakes in warfighters who are engaged in field operations.

Changes in weight loss and lipid profiles after a dietary purification program: a prospective case series

OBJECTIVE

The purpose of this case series was to describe immediate changes to weight and lipid profiles after a 21-day Standard Process whole food supplement and dietary modification program.

METHODS

Changes in weight and lipid profiles were measured for 7 participants (6 men and 1 woman) participating in a 21-day program. The dietary modifications throughout the Standard Process program were consumption of (1) unlimited fresh or frozen vegetables and fruits and preferably twice as many vegetables as fruits, (2) ½ to 1 cup of cooked lentils or brown rice each day, (3) 4 to 7 teaspoons of cold pressed oils per day, and (4) at least 64 oz of water a day. After day 10 of the program, participants were allowed to consume 1 to 2 servings of baked, broiled, or braised poultry or fish per day. Participants consumed a whey protein-based shake as meal replacement 2 times per day. Nutritional supplementation included a cleanse product on days 1 to 7, soluble fiber supplementation including oat bran concentrate and apple pectin on all days, and "green food" supplementation on days 8 to 21.

RESULTS

Weight loss ranged between 5.2 (2.4 kg) and 19.9 lb (9.0 kg) (average, 11.7 lb; 5.3 kg). Total cholesterol levels decreased with ranges between 11 and 77 mg/dL, and low-density lipoprotein cholesterol levels decreased in a range between 7 and 67 mg/dL.

CONCLUSION

After participating in a dietary program, the 7 participants demonstrated short-term weight loss and improvements in their lipid profiles.

Changes in anthropometric measurements, body composition, blood pressure, lipid profile, and testosterone in patients participating in a low-energy dietary intervention

OBJECTIVE

The purpose of this study was to describe changes in anthropometric measurements, body composition, blood pressure, lipid profile, and testosterone following a low-energy-density dietary intervention plus regimented supplementation program.

METHODS

The study design was a pre-post intervention design without a control group. Normal participants were recruited from the faculty, staff, students, and community members from a chiropractic college to participate in a 21-day weight loss program. All participants (n = 49; 36 women, 13 men; 31 ± 10.3 years of age) received freshly prepared mostly vegan meals (breakfast, lunch, and dinner) that included 1200 to 1400 daily calories (5020.8 to 5857.6 J) for the women and 1600 to 1800 (6694.4 to 7531.2 J) daily calories for the men. Nutritional supplements containing enzymes that were intended to facilitate digestion, reduce cholesterol levels, increase metabolic rate, and mediate inflammatory processes were consumed 30 minutes before each meal. The regimented supplementation program included once-daily supplementation with a green drink that contained alfalfa, wheatgrass, apple cider vinegar, and fulvic acid throughout the study period. A cleanse supplementation containing magnesium, chia, flaxseed, lemon, camu camu, cat's claw, bentonite clay, tumeric, pau d'arco, chanca piedra, stevia, zeolite clay, slippery elm, garlic, ginger, peppermint, aloe, citrus bioflavonoids, and fulvic acid was added before each meal during week 2. During week 3, the cleanse supplementation was replaced with probiotic and prebiotic supplementation.

RESULTS

Multiple paired t tests detected clinically meaningful reductions in weight (- 8.7 ± 5.54 lb) (- 3.9 ± 2.5 kg), total cholesterol (- 30.0 ± 29.77 mg/dL), and low-density lipoprotein cholesterol (- 21.0 ± 25.20 mg/dL) (P < .05). There was a pre-post intervention increase in testosterone for men (111.0 ± 121.13 ng/dL, P < .05).

CONCLUSIONS

Weight loss and improvements in total cholesterol and low-density lipoprotein cholesterol levels occurred after a low-energy-density dietary intervention plus regimented supplementation program.

miRNA analysis for the assessment of exercise and amino acid effects on human skeletal muscle

The study of micro RNA (miRNA) expression and function, a largely unexplored area of human muscle biology, may provide novel data regarding the development of targeted approaches that optimize skeletal muscle responses to exercise and amino acid manipulations. miRNAs are ubiquitously expressed, small noncoding RNAs that modulate posttranscriptional gene expression. Quantifying miRNA expression and predicting function as regulators of both single targets and complex networks is technically challenging and requires a combined approach of bioinformatics, molecular, and systems biology. Recent evidence suggests that the expression of muscle-specific miRNAs (myomirs), including miR-1, miR-133a/b, miR-206, and miR-499, is modulated by essential amino acid ingestion, endurance exercise, and endurance exercise training. The expression of miRNAs has also been implicated in the anabolic intracellular signaling and muscle hypertrophic response associated with resistance exercise training. Although these findings are intriguing, comprehensive human trials assessing functional outcomes associated with changes in miRNA expression in response to exercise and nutrition interventions have not been conducted. This article reviews the current understanding of miRNA biology and includes analytical techniques used to detect miRNA expression and methods to predict function. The intent is to provide the framework for future research studies that use miRNA analysis in an effort to elucidate optimal exercise and nutritional countermeasures for the prevention of muscle loss.

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

The purpose of this work was to determine the effects of varying levels of dietary protein on body composition and muscle protein synthesis during energy deficit (ED). A randomized controlled trial of 39 adults assigned the subjects diets providing protein at 0.8 (recommended dietary allowance; RDA), 1.6 (2×-RDA), and 2.4 (3×-RDA) g kg(-1) d(-1) for 31 d. A 10-d weight-maintenance (WM) period was followed by a 21 d, 40% ED. Body composition and postabsorptive and postprandial muscle protein synthesis were assessed during WM (d 9-10) and ED (d 30-31). Volunteers lost (P<0.05) 3.2 ± 0.2 kg body weight during ED regardless of dietary protein. The proportion of weight loss due to reductions in fat-free mass was lower (P<0.05) and the loss of fat mass was higher (P<0.05) in those receiving 2×-RDA and 3×-RDA compared to RDA. The anabolic muscle response to a protein-rich meal during ED was not different (P>0.05) from WM for 2×-RDA and 3×-RDA, but was lower during ED than WM for those consuming RDA levels of protein (energy × protein interaction, P<0.05). To assess muscle protein metabolic responses to varied protein intakes during ED, RDA served as the study control. In summary, we determined that consuming dietary protein at levels exceeding the RDA may protect fat-free mass during short-term weight loss.

Normal vs. high-protein weight loss diets in men: effects on body composition and indices of metabolic syndrome

OBJECTIVE

This study assessed the effectiveness of a prescribed weight-loss diet with 0.8 versus 1.4 g protein·kg(-1) day(-1) on changes in weight, body composition, indices of metabolic syndrome, and resting energy expenditure (REE) in overweight and obese men.

DESIGN AND METHODS

Men were randomized to groups that consumed diets containing 750 kcal day(-1) less than daily energy needs for weight maintenance with either normal protein (NP, n = 21) or higher protein (HP, n = 22) content for 12 weeks. The macronutrient distributions of the NP and HP diets were 25:60:15, and 25:50:25 percent energy from fat, carbohydrate, and protein, respectively. Assessments were made pre and post intervention. The subjects were retrospectively subgrouped into overweight and obese groups.

RESULTS AND CONCLUSION

Both diet groups lost comparable body weight and fat. The HP group lost less lean body mass than the NP group (-1.9 ± 0.3 vs. -3.0 ± 0.4 kg). The effects of protein and BMI status on lean body mass loss were additive. The reductions in total cholesterol, HDL-C, triacylglycerol, glucose, and insulin, along with LDL-C, total cholesterol-to-HDL-C ratio, and HOMA-IR, were not statistically different between NP and HP. Likewise, macronutrient distributions of the diet did not affect the reductions in REE, and blood pressure. In conclusion, energy restriction effectively improves multiple clinical indicators of cardiovascular health and glucose control, and consumption of a higher-protein diet and accomplishing weight loss when overweight versus obese help men preserve lean body mass over a short period of time.

Effects of easy-to-use protein-rich energy bar on energy balance, physical activity and performance during 8 days of sustained physical exertion

BACKGROUND

Previous military studies have shown an energy deficit during a strenuous field training course (TC). This study aimed to determine the effects of energy bar supplementation on energy balance, physical activity (PA), physical performance and well-being and to evaluate ad libitum fluid intake during wintertime 8-day strenuous TC.

METHODS

Twenty-six men (age 20±1 yr.) were randomly divided into two groups: The control group (n = 12) had traditional field rations and the experimental (Ebar) group (n = 14) field rations plus energy bars of 4.1 MJ•day(-1). Energy (EI) and water intake was recorded. Fat-free mass and water loss were measured with deuterium dilution and elimination, respectively. The energy expenditure was calculated using the intake/balance method and energy availability as (EI/estimated basal metabolic rate). PA was monitored using an accelerometer. Physical performance was measured and questionnaires of upper respiratory tract infections (URTI), hunger and mood state were recorded before, during and after TC.

RESULTS

Ebar had a higher EI and energy availability than the controls. However, decreases in body mass and fat mass were similar in both groups representing an energy deficit. No differences were observed between the groups in PA, water balance, URTI symptoms and changes in physical performance and fat-free mass. Ebar felt less hunger after TC than the controls and they had improved positive mood state during the latter part of TC while controls did not. Water deficit associated to higher PA. Furthermore, URTI symptoms and negative mood state associated negatively with energy availability and PA.

CONCLUSION

An easy-to-use protein-rich energy bars did not prevent energy deficit nor influence PA during an 8-day TC. The high content of protein in the bars might have induced satiation decreasing energy intake from field rations. PA and energy intake seems to be primarily affected by other factors than energy supplementation such as mood state.

Dietary protein to maximize resistance training: a review and examination of protein spread and change theories

An appreciable volume of human clinical data supports increased dietary protein for greater gains from resistance training, but not all findings are in agreement. We recently proposed "protein spread theory" and "protein change theory" in an effort to explain discrepancies in the response to increased dietary protein in weight management interventions. The present review aimed to extend "protein spread theory" and "protein change theory" to studies examining the effects of protein on resistance training induced muscle and strength gains. Protein spread theory proposed that there must have been a sufficient spread or % difference in g/kg/day protein intake between groups during a protein intervention to see muscle and strength differences. Protein change theory postulated that for the higher protein group, there must be a sufficient change from baseline g/kg/day protein intake to during study g/kg/day protein intake to see muscle and strength benefits. Seventeen studies met inclusion criteria. In studies where a higher protein intervention was deemed successful there was, on average, a 66.1% g/kg/day between group intake spread versus a 10.2% g/kg/day spread in studies where a higher protein diet was no more effective than control. The average change in habitual protein intake in studies showing higher protein to be more effective than control was +59.5% compared to +6.5% when additional protein was no more effective than control. The magnitudes of difference between the mean spreads and changes of the present review are similar to our previous review on these theories in a weight management context. Providing sufficient deviation from habitual intake appears to be an important factor in determining the success of additional protein in enhancing muscle and strength gains from resistance training. An increase in dietary protein favorably effects muscle and strength during resistance training.

Dietary protein requirements and adaptive advantages in athletes

Dietary guidelines from a variety of sources are generally congruent that an adequate dietary protein intake for persons over the age of 19 is between 0·8–0·9 g protein/kg body weight/d. According to the US/Canadian Dietary Reference Intakes, the RDA for protein of 0·8 g protein/kg/d is “…the average daily intake level that is sufficient to meet the nutrient requirement of nearly all [~98 %]… healthy individuals…” The panel also states that “…no additional dietary protein is suggested for healthy adults undertaking resistance or endurance exercise.” These recommendations are in contrast to recommendations from the US and Canadian Dietetic Association: “Protein recommendations for endurance and strength trained athletes range from 1·2 to 1·7 g/kg/d.” The disparity between those setting dietary protein requirements and those who might be considered to be making practical recommendations for athletes is substantial. This may reflect a situation where an adaptive advantage of protein intakes higher than recommended protein requirements exists. That population protein requirements are still based on nitrogen balance may also be a point of contention since achieving balanced nitrogen intake and excretion likely means little to an athlete who has the primary goal of exercise performance. The goal of the present review is to critically analyse evidence from both acute and chronic dietary protein-based studies in which athletic performance, or correlates thereof, have been measured. An attempt will be made to distinguish between protein requirements set by data from nitrogen balance studies, and a potential adaptive ‘advantage’ for athletes of dietary protein in excess of the RDA.

Dietary protein for athletes: from requirements to optimum adaptation

Opinion on the role of protein in promoting athletic performance is divided along the lines of how much aerobic-based versus resistance-based activity the athlete undertakes. Athletes seeking to gain muscle mass and strength are likely to consume higher amounts of dietary protein than their endurance-trained counterparts. The main belief behind the large quantities of dietary protein consumption in resistance-trained athletes is that it is needed to generate more muscle protein. Athletes may require protein for more than just alleviation of the risk for deficiency, inherent in the dietary guidelines, but also to aid in an elevated level of functioning and possibly adaptation to the exercise stimulus. It does appear, however, that there is a good rationale for recommending to athletes protein intakes that are higher than the RDA. Our consensus opinion is that leucine, and possibly the other branched-chain amino acids, occupy a position of prominence in stimulating muscle protein synthesis; that protein intakes in the range of 1.3-1.8 g · kg(-1) · day(-1) consumed as 3-4 isonitrogenous meals will maximize muscle protein synthesis. These recommendations may also be dependent on training status: experienced athletes would require less, while more protein should be consumed during periods of high frequency/intensity training. Elevated protein consumption, as high as 1.8-2.0 g · kg(-1) · day(-1) depending on the caloric deficit, may be advantageous in preventing lean mass losses during periods of energy restriction to promote fat loss.

Increased consumption of dairy foods and protein during diet- and exercise-induced weight loss promotes fat mass loss and lean mass gain in overweight and obese premenopausal women

Weight loss can have substantial health benefits for overweight or obese persons; however, the ratio of fat:lean tissue loss may be more important. We aimed to determine how daily exercise (resistance and/or aerobic) and a hypoenergetic diet varying in protein and calcium content from dairy foods would affect the composition of weight lost in otherwise healthy, premenopausal, overweight, and obese women. Ninety participants were randomized to 3 groups (n = 30/group): high protein, high dairy (HPHD), adequate protein, medium dairy (APMD), and adequate protein, low dairy (APLD) differing in the quantity of total dietary protein and dairy food-source protein consumed: 30 and 15%, 15 and 7.5%, or 15 and <2% of energy, respectively. Body composition was measured by DXA at 0, 8, and 16 wk and MRI (n = 39) to assess visceral adipose tissue (VAT) volume at 0 and 16 wk. All groups lost body weight (P < 0.05) and fat (P < 0.01); however, fat loss during wk 8-16 was greater in the HPHD group than in the APMD and APLD groups (P < 0.05). The HPHD group gained lean tissue with a greater increase during 8-16 wk than the APMD group, which maintained lean mass and the APLD group, which lost lean mass (P < 0.05). The HPHD group also lost more VAT as assessed by MRI (P < 0.05) and trunk fat as assessed by DXA (P < 0.005) than the APLD group. The reduction in VAT in all groups was correlated with intakes of calcium (r = 0.40; P < 0.05) and protein (r = 0.32; P < 0.05). Therefore, diet- and exercise-induced weight loss with higher protein and increased dairy product intakes promotes more favorable body composition changes in women characterized by greater total and visceral fat loss and lean mass gain.

Nutrition guidelines for strength sports: sprinting, weightlifting, throwing events, and bodybuilding

Strength and power athletes are primarily interested in enhancing power relative to body weight and thus almost all undertake some form of resistance training. While athletes may periodically attempt to promote skeletal muscle hypertrophy, key nutritional issues are broader than those pertinent to hypertrophy and include an appreciation of the sports supplement industry, the strategic timing of nutrient intake to maximize fuelling and recovery objectives, plus achievement of pre-competition body mass requirements. Total energy and macronutrient intakes of strength-power athletes are generally high but intakes tend to be unremarkable when expressed relative to body mass. Greater insight into optimization of dietary intake to achieve nutrition-related goals would be achieved from assessment of nutrient distribution over the day, especially intake before, during, and after exercise. This information is not readily available on strength-power athletes and research is warranted. There is a general void of scientific investigation relating specifically to this unique group of athletes. Until this is resolved, sports nutrition recommendations for strength-power athletes should be directed at the individual athlete, focusing on their specific nutrition-related goals, with an emphasis on the nutritional support of training.

Efficacy and consequences of very-high-protein diets for athletes and exercisers

Athletes and exercisers have utilised high-protein diets for centuries. The objective of this review is to examine the evidence for the efficacy and potential dangers of high-protein diets. One important factor to consider is the definition of a ‘high-protein diet’. There are several ways to consider protein content of a diet. The composition of the diet can be determined as the absolute amount of the protein (or other nutrient of interest), the % of total energy (calories) as protein and the amount of protein ingested per kg of body weight. Many athletes consume very high amounts of protein. High-protein diets most often are associated with muscle hypertrophy and strength, but now also are advocated for weight loss and recovery from intense exercise or injuries. Prolonged intake of a large amount of protein has been associated with potential dangers, such as bone mineral loss and kidney damage. In otherwise healthy individuals, there is little evidence that high protein intake is dangerous. However, kidney damage may be an issue for individuals with already existing kidney dysfunction. Increased protein intake necessarily means that overall energy intake must increase or consumption of either carbohydrate or fat must decrease. In conclusion, high protein intake may be appropriate for some athletes, but there are potential negative consequences that must be carefully considered before adopting such a diet. In particular, care must be taken to ensure that there is sufficient intake of other nutrients to support the training load.

Protein intake, body composition, and protein status following bariatric surgery

BACKGROUND

Daily protein intake recommendations have recently been proposed for the bariatric patient. We aimed to evaluate the accomplishment of these recommendations, and the influence of protein intake (PI) on fat free mass (FFM) and protein status changes following bariatric surgery.

METHODS

We examined 101 consecutive patients undergoing laparoscopic Roux-in-Y gastric gypass (LGBP) or laparoscopic sleeve gastrectomy (LSG). Based on 3-day food records, PI from food and supplements were quantified at 4, 8, and 12 months after surgery. The association between PI and body composition (bioelectrical impedance), plasma albumin and pre-albumin was evaluated at all study time points.

RESULTS

A PI <60 g/day was present respectively in 45%, 35%, and 37% of the cohort at 4, 8, and 12 months after surgery (p < 0.001 relative to baseline). Despite our universal recommendation of protein supplementation, supplements were taken only by 63.4, 50.5, and 33.7% of the participants at 4, 8, and 12 months. However, protein supplementation was effective in helping patients to achieve the daily protein intake goal. In linear regression analysis, male gender and weight loss, but not PI, were significantly associated with loss of FFM (p < 0.001). No significant correlation between PI and plasma albumin or pre-albumin was found.

CONCLUSIONS

Our study underscores the value of protein supplementation for the achievement of the recommended daily protein intake in the bariatric patient. However, our data does not help to define a PI goal as critical in determining the FFM and protein status changes following LGBP or LSG.