Role of leucine in protein metabolism during exercise and recovery

BCAAs acutely drive glucose dysregulation and insulin resistance: role of AgRP neurons

BACKGROUND

High-protein diets are often enriched with branched-chain amino acids (BCAAs) known to enhance protein synthesis and provide numerous physiological benefits, but recent studies reveal their association with obesity and diabetes. In support of this, protein or BCAA supplementation is shown to disrupt glucose metabolism while restriction improves it. However, it is not clear if these are primary, direct effects of BCAAs or secondary to other physiological changes during chronic manipulation of dietary BCAAs.

METHODS

Three-month-old C57Bl/6 mice were acutely treated with either vehicle/BCAAs or BT2, a BCAA-lowering compound, and detailed in vivo metabolic phenotyping, including frequent sampling and pancreatic clamps, were conducted.

RESULTS

Using a catheter-guided frequent sampling method in mice, here we show that a single infusion of BCAAs was sufficient to acutely elevate blood glucose and plasma insulin. While pre-treatment with BCAAs did not affect glucose tolerance, a constant infusion of BCAAs during hyperinsulinemic-euglycemic clamps impaired whole-body insulin sensitivity. Similarly, a single injection of BT2 was sufficient to prevent BCAA rise during fasting and markedly improve glucose tolerance in high-fat-fed mice, suggesting that abnormal glycemic control in obesity may be causally linked to high circulating BCAAs. We further show that chemogenetic over-activation of AgRP neurons in the hypothalamus, as present in obesity, significantly impairs glucose tolerance that is completely normalized by acute BCAA reduction. Interestingly, most of these effects were demonstrated only in male, but not in female mice.

CONCLUSION

These findings suggest that BCAAs per se can acutely impair glucose homeostasis and insulin sensitivity, thus offering an explanation for how they may disrupt glucose metabolism in the long-term as observed in obesity and diabetes. Our findings also reveal that AgRP neuronal regulation of blood glucose is mediated through BCAAs, further elucidating a novel mechanism by which brain controls glucose homeostasis.

Association of postprandial postexercise muscle protein synthesis rates with dietary leucine: A systematic review

BACKGROUND

Dietary protein ingestion augments post (resistance) exercise muscle protein synthesis (MPS) rates. It is thought that the dose of leucine ingested within the protein (leucine threshold hypothesis) and the subsequent plasma leucine variables (leucine trigger hypothesis; peak magnitude, rate of rise, and total availability) determine the magnitude of the postprandial postexercise MPS response.

METHODS

A quantitative systematic review was performed extracting data from studies that recruited healthy adults, applied a bout of resistance exercise, ingested a bolus of protein within an hour of exercise, and measured plasma leucine concentrations and MPS rates (delta change from basal).

RESULTS

Ingested leucine dose was associated with the magnitude of the MPS response in older, but not younger, adults over acute (0-2 h, r2  = 0.64, p = 0.02) and the entire postprandial (>2 h, r2  = 0.18, p = 0.01) period. However, no single plasma leucine variable possessed substantial predictive capacity over the magnitude of MPS rates in younger or older adults.

CONCLUSION

Our data provide support that leucine dose provides predictive capacity over postprandial postexercise MPS responses in older adults. However, no threshold in older adults and no plasma leucine variable was correlated with the magnitude of the postexercise anabolic response.

Impacts of microgravity on amino acid metabolism during spaceflight

Spaceflight exerts an extreme and unique influence on human physiology as astronauts are subjected to long-term or short-term exposure to microgravity. During spaceflight, a multitude of physiological changes, including the loss of skeletal muscle mass, bone resorption, oxidative stress, and impaired blood flow, occur, which can affect astronaut health and the likelihood of mission success. In vivo and in vitro metabolite studies suggest that amino acids are among the most affected nutrients and metabolites by microgravity (a weightless condition due to very weak gravitational forces). Moreover, exposure to microgravity alters gut microbial composition, immune function, musculoskeletal health, and consequently amino acid metabolism. Appropriate knowledge of daily protein consumption, with a focus on specific functional amino acids, may offer insight into potential combative and/or therapeutic effects of amino acid consumption in astronauts and space travelers. This will further aid in the successful development of long-term manned space mission and permanent space habitats.

Physiological and molecular sex differences in human skeletal muscle in response to exercise training

Sex differences in exercise physiology, such as substrate metabolism and skeletal muscle fatigability, stem from inherent biological factors, including endogenous hormones and genetics. Studies investigating exercise physiology frequently include only males or do not take sex differences into consideration. Although there is still an underrepresentation of female participants in exercise research, existing studies have identified sex differences in physiological and molecular responses to exercise training. The observed sex differences in exercise physiology are underpinned by the sex chromosome complement, sex hormones and, on a molecular level, the epigenome and transcriptome. Future research in the field should aim to include both sexes, control for menstrual cycle factors, conduct large-scale and ethnically diverse studies, conduct meta-analyses to consolidate findings from various studies, leverage unique cohorts (such as post-menopausal, transgender, and those with sex chromosome abnormalities), as well as integrate tissue and cell-specific -omics data. This knowledge is essential for developing deeper insight into sex-specific physiological responses to exercise training, thus directing future exercise physiology studies and practical application.

Evaluation of a Supervised Adapted Physical Activity Program Associated or Not with Oral Supplementation with Arginine and Leucine in Subjects with Obesity and Metabolic Syndrome: A Randomized Controlled Trial

Background: In patients with obesity and metabolic syndrome (MetS), lifestyle interventions combining diet, in particular, and physical exercise are recommended as the first line treatment. Previous studies have suggested that leucine or arginine supplementation may have beneficial effects on the body composition or insulin sensitivity and endothelial function, respectively. We thus conducted a randomized controlled study to evaluate the effects of a supervised adapted physical activity program associated or not with oral supplementation with leucine and arginine in MetS-complicated patients with obesity. Methods: Seventy-nine patients with obesity and MetS were randomized in four groups: patients receiving arginine and leucine supplementation (ALs group, n = 20), patients on a supervised adapted physical activity program (APA group, n = 20), patients combining ALs and APA (ALs+APA group, n = 20), and a control group (n = 19). After the baseline evaluation (m0), patients received ALs and/or followed the APA program for 6 months (m6). Body composition, MetS parameters, lipid and glucose metabolism markers, inflammatory markers, and a cardiopulmonary exercise test (CPET) were assessed at m0, m6, and after a 3-month wash-out period (m9). Results: After 6 months of intervention, we did not observe variable changes in body weight, body composition, lipid and glucose metabolism markers, inflammatory parameters, or quality of life scores between the four groups. However, during the CPET, the maximal power (Pmax and Ppeak), power, and O2 consumption at the ventilatory threshold (P(VT) and O2(VT)) were improved in the APA and ALs+APA groups (p < 0.05), as well as the forced vital capacity (FVC). Between m6 and m9, a gain in fat mass was only observed in patients in the APA and ALs+APA groups. Conclusion: In our randomized controlled trial, arginine and leucine supplementation failed to improve MetS in patients with obesity, as did the supervised adapted physical activity program and the combination of both. Only the cardiorespiratory parameters were improved by exercise training.

Paradigm shift in gastrointestinal surgery − combating sarcopenia with prehabilitation: Multimodal review of clinical and scientific data

A growing body of evidence has demonstrated the prognostic significance of sarcopenia in surgical patients as an independent predictor of postoperative complications and outcomes. These included an increased risk of total complications, major complications, re-admissions, infections, severe infections, 30 d mortality, longer hospital stay and increased hospitalization expenditures. A program to enhance recovery after surgery was meant to address these complications; however, compliance to the program since its introduction has been less than ideal. Over the last decade, the concept of prehabilitation, or “pre-surgery rehabilitation”, has been discussed. The presurgical period represents a window of opportunity to boost and optimize the health of an individual, providing a compensatory “buffer” for the imminent reduction in physiological reserve post-surgery. Initial results have been promising. We review the literature to critically review the utility of prehabilitation, not just in the clinical realm, but also in the scientific realm, with a resource management point-of-view.

The Effect of Lactobacillus plantarum CQPC02 on Fatigue and Biochemical Oxidation Levels in a Mouse Model of Physical Exhaustion

Chinese Sichuan pickle is a fermented food rich in microorganisms. Microorganisms have the potential to become an important new form of potent future therapeutic capable of treating human disease. Selecting vitamin C as a positive control, a lactic acid bacteria (Lactobacillus plantarum CQPC02, LP-CQPC02) isolated from Sichuan pickle was given to mice over 4 weeks to investigate the effect of CQPC02 on fatigue levels and biochemical oxidation phenomena in exercise-exhausted Institute of Cancer Research (ICR) mice. The fatigue model was established by forced swimming of mice, the levels of hepatic glycogen, skeletal muscle glycogen, lactic acid, blood urea nitrogen and free fatty acid were measured by physicochemical methods, serum serum creatine kinase (CK), aspartate aminotransferase (AST) and alanine aminotransferase (ALT), superoxide dismutase (SOD), catalase (CAT) and malondialdehyde (MDA) levels were measured by kits, the histopathological changes in the livers of mice were observed by H&E slicing, and the mRNA changes in the livers and skeletal muscles were observed by quantitative polymerase chain reaction (qPCR). Both vitamin C and LP-CQPC02 increased swimming exhaustion time. The concentration of LP-CQPC02 and exhaustion time were positively correlated. LP-CQPC02 also increased liver glycogen, skeletal muscle glycogen and free fatty acid content in mice and reduced lactic acid and blood urea nitrogen content in a dose-dependent manner. As walnut albumin antioxidant peptide concentration increased, levels of mouse CK, AST, and AST gradually decreased. LP-CQPC02 increased SOD and CAT levels and decreased MDA levels in a dose-dependent fashion. LP-CQPC02 up-regulated expression of mRNA encoding copper/zinc-superoxide dismutase (Cu/Zn-SOD), manganese-superoxide dismutase (Mn-SOD), and CAT in swimming exhaustion mouse liver tissue. LP-CQPC02 also up-regulated alanine/serine/cysteine/threonine transporter 1 (ASCT1) expression while down-regulating syncytin-1, inducible nitric oxide synthase (iNOS), tumor necrosis factor-alpha (TNF-α) expression in swimming exhaustion mouse skeletal muscle. Overall, LP-CQPC02 had a clear anti-fatigue and anti-oxidation effect. This suggests that LP-CQPC02 can be developed as a microbiological therapeutic agent.

Short-term branched-chain amino acid supplementation does not enhance vertical jump in professional volleyball players. A double-blind, controlled, randomized study

Introduction

To the best of the authors' knowledge, no previous studies have described the effect of branched-chain amino acids (BCAA) on vertical performance during a week in professional volleyball players. This study assessed BCAA supplementation for a week, aiming to improve vertical jump performance in male professional volleyball players. Twelve male volleyballers were randomly assigned to a BCAA group (n = 6) or a control group (n = 6). The BCAA group ingested 21 g over a week, 7 g per day on Monday, Wednesday, and Friday, before a volleyball training session, while the control group drank a placebo drink. Participants performed 8 maximal countermovement jumps (CMJ); the 3 CMJs on Monday and Wednesday were evaluated after warm-up, after plyometric training, and at the end of the training session; and the 2 CMJs on Friday were evaluated after warm-up, and at the end of the training session. Compared with baseline, no significant differences in CMJ over the week were observed in BCAA or control group, neither between groups. The results indicated that 21 g of BCAA supplementation over a week did not improve vertical jump performance in professional volleyball players.

Nutrition for Master Athletes: Is There a Need for Specific Recommendations?

Master athletes are often considered exemplars of successful aging, thanks to their capacity to maintain a high sports performance during their entire life. A high training capacity, regular participation in sporting competitions, and delayed alterations in body composition and physiological capacities have been listed among the main factors contributing to impressive master athletes' performances. However, there is a paucity of data on the metabolism and dietary habits of master athletes, and the question of whether they need to adapt their nutrition to the aging process remains open. Herein, the authors presented a contemporary overview of the metabolic challenges associated with aging, including the risk of low energy availability, anabolic resistance, and periods of metabolic crisis due to forced immobilization. After assembling scientific evidence to show that master athletes must adapt their dietary intake, the authors proposed a summary of nutritional recommendations for master athletes and suggested the next stage of research.

Endoplasmic reticulum retention signaling and transmembrane channel proteins predicted for oilseed ω3 fatty acid desaturase 3 (FAD3) genes

Oilseed crop oils contain a variety of unsaturated fatty acids that are synthesized and regulated by fatty acid desaturases (FADs). In this study, 14 FAD3 (ω3 desaturase) protein sequences from oilseeds are analyzed and presented through the application of several computational tools. The results indicated a close relationship between Brassica napus and Camelina sativa, as well as between Salvia hispanica and Perilla frutescens FAD3s, due to a high similarity in codon preferences in codon usage clusters and the phylogenetic tree. The cis-acting element results reveal that the seed-specific promoter region of BnFAD3 contains the critical conserved boxes such as HSE and ABRE, which are involved in responsiveness to heat stress and abscisic acid. The presence of the aforementioned conserved boxes may increase cold acclimation as well as tolerance to drought and high salinity. Omega(ω)3 desaturases contain a Skn-1 motif which is a cis-acting regulatory element required involved in endosperm development. In oilseed FAD3s, leucine is the most repeated amino acid in FAD3 proteins. The study conveyed that B. napus, Camelina sativa, Linum usitatissimum, Vernicia fordii, Gossypium hirsutum, S. hispanica, Cannabis sativa, and P. frutescens have retention signal KXKXX/XKXX at their c-terminus sites, which is one of the most important characteristics of FADs. Additionally, it was found that BnFAD3 is a transmembrane protein that can convert ω6 to ω3 fatty acids and may simultaneously act as a potassium ion channel in the ER.

Effects of β-hydroxy-β-methylbutyrate (HMB) supplementation in addition to multicomponent exercise in adults older than 70 years living in nursing homes, a cluster randomized placebo-controlled trial: the HEAL study protocol

Background

Evidence supports the fact that multicomponent exercise and HMB supplementation are, separately, effective in improving older adult’s health and palliate functional metabolic diseases in older people. However, the true effect of HMB supplementation combined with a tailored exercise program in frail older adults is still unknown. Thus, the aim of the HEAL (HMB + Exercise = Adults Living longer) study is to assess the effects of the combination of a daily multicomponent exercise and resistance training (VIVIFRAIL program) intervention in addition to HMB supplementation on older adults’ health.

Methods/design

A 24-week cluster randomized, double-blind, placebo-controlled study will be conducted on 104 adults ≥70 years. Nursing homes will be randomized to either of four groups: Ex-HMB (exercise intervention with HMB), Ex-Plac (exercise intervention with placebo), NoEx-HMB (no exercise intervention with HMB), and Controls (No exercise and no HMB). Intervention groups which include exercise will complete the individualized multicomponent (strength, balance and cardiovascular exercises) training program VIVIFRAIL. Intervention groups which include HMB supplementation will receive a 3 g/daily dose of free acid HMB in powder form. The primary outcome measure is the functional capacity. Secondary outcome measures are muscle strength and power, frailty and fall risk, body composition, biochemical analyses and cardiometabolic risk factor, disability and comorbidity, cognitive function and depression.

Discussion

The findings of the HEAL study will help professionals from public health systems to identify cost-effective and innovative actions to improve older people’s health and quality of life, and endorse exercise practice in older adults and people living in nursing homes.

Trial registration

NCT03827499; Date of registration: 01/02/2019.

The cross-tissue metabolic response of abalone (Haliotis midae) to functional hypoxia

Functional hypoxia is a stress condition caused by the abalone itself as a result of increased muscle activity, which generally necessitates the employment of anaerobic metabolism if the activity is sustained for prolonged periods. With that being said, abalone are highly reliant on anaerobic metabolism to provide partial compensation for energy production during oxygen-deprived episodes. However, current knowledge on the holistic metabolic response for energy metabolism during functional hypoxia, and the contribution of different metabolic pathways and various abalone tissues towards the overall accumulation of anaerobic end-products in abalone are scarce. Metabolomics analysis of adductor muscle, foot muscle, left gill, right gill, haemolymph and epipodial tissue samples indicated that South African abalone (Haliotis midae) subjected to functional hypoxia utilises predominantly anaerobic metabolism, and depends on all of the main metabolite classes (proteins, carbohydrates and lipids) for energy supply. Functional hypoxia caused increased levels of anaerobic end-products: lactate, alanopine, tauropine, succinate and alanine. Also, elevation in arginine levels was detected, confirming that abalone use phosphoarginine to generate energy during functional hypoxia. Different tissues showed varied metabolic responses to hypoxia, with functional hypoxia showing excessive changes in the adductor muscle and gills. From this metabolomics investigation, it becomes evident that abalone are metabolically able to produce sufficient amounts of energy when functional hypoxia is experienced. Also, tissue interplay enables the adjustment of H. midae energy requirements as their metabolism shifts from aerobic to anaerobic respiration during functional hypoxia.

This article has an associated First Person interview with the first author of the paper.

Summary: We report, for the first time, a metabolic map of abalone metabolism in response to functional hypoxia, compiled from results obtained by metabolomics analysis.

International Society of Sports Nutrition Position Stand: protein and exercise

The International Society of Sports Nutrition (ISSN) provides an objective and critical review related to the intake of protein for healthy, exercising individuals. Based on the current available literature, the position of the Society is as follows:An acute exercise stimulus, particularly resistance exercise, and protein ingestion both stimulate muscle protein synthesis (MPS) and are synergistic when protein consumption occurs before or after resistance exercise.For building muscle mass and for maintaining muscle mass through a positive muscle protein balance, an overall daily protein intake in the range of 1.4-2.0 g protein/kg body weight/day (g/kg/d) is sufficient for most exercising individuals, a value that falls in line within the Acceptable Macronutrient Distribution Range published by the Institute of Medicine for protein.Higher protein intakes (2.3-3.1 g/kg/d) may be needed to maximize the retention of lean body mass in resistance-trained subjects during hypocaloric periods.There is novel evidence that suggests higher protein intakes (>3.0 g/kg/d) may have positive effects on body composition in resistance-trained individuals (i.e., promote loss of fat mass).Recommendations regarding the optimal protein intake per serving for athletes to maximize MPS are mixed and are dependent upon age and recent resistance exercise stimuli. General recommendations are 0.25 g of a high-quality protein per kg of body weight, or an absolute dose of 20-40 g.Acute protein doses should strive to contain 700-3000 mg of leucine and/or a higher relative leucine content, in addition to a balanced array of the essential amino acids (EAAs).These protein doses should ideally be evenly distributed, every 3-4 h, across the day.The optimal time period during which to ingest protein is likely a matter of individual tolerance, since benefits are derived from pre- or post-workout ingestion; however, the anabolic effect of exercise is long-lasting (at least 24 h), but likely diminishes with increasing time post-exercise.While it is possible for physically active individuals to obtain their daily protein requirements through the consumption of whole foods, supplementation is a practical way of ensuring intake of adequate protein quality and quantity, while minimizing caloric intake, particularly for athletes who typically complete high volumes of training. Rapidly digested proteins that contain high proportions of essential amino acids (EAAs) and adequate leucine, are most effective in stimulating MPS. Different types and quality of protein can affect amino acid bioavailability following protein supplementation. Athletes should consider focusing on whole food sources of protein that contain all of the EAAs (i.e., it is the EAAs that are required to stimulate MPS). Endurance athletes should focus on achieving adequate carbohydrate intake to promote optimal performance; the addition of protein may help to offset muscle damage and promote recovery. Pre-sleep casein protein intake (30-40 g) provides increases in overnight MPS and metabolic rate without influencing lipolysis.

Reduced muscular fatigue after a 12-week leucine-rich amino acid supplementation combined with moderate training in elderly: a randomised, placebo-controlled, double-blind trial

Background

Age-related muscle loss is characterised by a progressing decrease in muscle mass, strength and function. Besides resistance training and physical activity, appropriate nutrition that is rich in protein, especially branched-chain amino acids, is very important to support training effects and positively influence the protein synthesis to degradation ratio.

Aim

The purpose of this study was to evaluate the effect of a 12-week leucine-rich amino acid supplementation in combination with moderate training.

Methods

Forty-eight healthy subjects exercised for 30 min three times per week and received either a leucine-rich amino acid supplementation or a placebo. Before and after supplementation, volunteers performed an exhaustive eccentric exercise protocol. Maximal concentric strength, muscle soreness, creatine kinase (CK), type II collagen collagenase cleavage neoepitope (C2C), C propeptide of type II procollagen (CP2) and safety assessments were performed before exercise and after 3, 24, 48 and 72 hours.

Results

The supplementation with leucine resulted in reduced loss of strength at 0 and 3 hours after downhill walking compared with the placebo (p=0.0439). The reduction of C2C/CP2 ratio deflection was significantly increased (p=0.038) due to leucine compared with the placebo. The same tendency could be observed for the recovery phase. No significant supplement effects for muscle soreness and CK could be observed.

Conclusion

The principle findings show that leucine-rich amino acid supplementation can counteract the negative effects of eccentric exercise. The treatment resulted in a reduction of exercise-induced strength loss.

Greater Amino Acid Intake Is Required to Maximize Whole-Body Protein Synthesis Immediately after Endurance Exercise Than at Rest in Endurance-Trained Rats, as Determined by an Indicator Amino Acid Oxidation Method

BACKGROUND

The indicator amino acid oxidation (IAAO) method has contributed to establishing protein and amino acid (AA) requirements by determining the optimal protein and AA intake that maximizes whole-body protein synthesis. However, it has not been used with endurance-trained subjects.

OBJECTIVE

This study aimed to determine the optimal AA intake immediately after endurance exercise and at rest in endurance-trained rats by using the IAAO method.

METHODS

Four-week-old male Fischer rats were divided into a sedentary (SED) group and a trained (TR) group, which underwent treadmill training 5 d/wk for 6 wk at 26 m/min for 60 min/d. On the metabolic trial day, half of the TR group was provided with test diets after daily treadmill running (TR-PostEx). The other half of the TR group (TR-Rest) and all of the SED group were provided with test diets while at rest. The test diets contained different amounts of AAs (3.3-37.3 g ⋅ kg(-1) ⋅ d(-1)). Phenylalanine in the test diet was replaced with L-[1-(13)C]phenylalanine. The phenylalanine oxidation rate (PheOx) was determined with (13)CO2 enrichment in breath, CO2 excretion rate, and enrichment of phenylalanine in blood during the feeding period. The optimal AA intake was determined with biphasic mixed linear regression crossover analysis for PheOx, which identified a breakpoint at the minimal PheOx in response to graded amounts of AA intake.

RESULTS

The optimal AA intake in the TR-PostEx group (26.8 g ⋅ kg(-1) ⋅ d(-1); 95% CI: 21.5, 32.1 g ⋅ kg(-1) ⋅ d(-1)) was significantly higher than in the SED (15.1 g ⋅ kg(-1) ⋅ d(-1); 95% CI: 11.1, 19.1 g ⋅ kg(-1) ⋅ d(-1)) and TR-Rest (13.3 g ⋅ kg(-1) ⋅ d(-1); 95% CI: 10.9, 15.7 g ⋅ kg(-1) ⋅ d(-1)) groups, which did not differ.

CONCLUSIONS

Greater AA intake is required to maximize whole-body protein synthesis immediately after endurance exercise than at rest, but not at rest in endurance-trained rats.

Dairy products, yogurt consumption, and cardiometabolic risk in children and adolescents

The high prevalence of obesity in children is a global health issue. Obesity in children and adolescents can result in hypertension, dyslipidemia, chronic inflammation, and hyperinsulinemia, increasing the risk of death, as children grow into adulthood, and raising public health concerns. Type 2 diabetes in children and adolescents is a cardiovascular disease (CVD) risk factor. Dairy consumption may have a protective effect against the development of CVD, but there is scarce evidence of this in children and adolescents. Within the Healthy Lifestyle in Europe by Nutrition in Adolescence, the objective of this study was to investigate the relationship between dairy consumption and CVD risk factors in a sample of adolescents (aged 12.5-17.5 years) from 8 European cities. Overall, dairy products emerged as the food group that best identified adolescents at low CVD risk. Higher consumption of milk and yogurt and of milk- and yogurt-based beverages was associated with lower body fat, lower risk for CVD, and higher cardiorespiratory fitness.

The Link between Dietary Protein Intake, Skeletal Muscle Function and Health in Older Adults

Skeletal muscle mass and function are progressively lost with age, a condition referred to as sarcopenia. By the age of 60, many older adults begin to be affected by muscle loss. There is a link between decreased muscle mass and strength and adverse health outcomes such as obesity, diabetes and cardiovascular disease. Data suggest that increasing dietary protein intake at meals may counterbalance muscle loss in older individuals due to the increased availability of amino acids, which stimulate muscle protein synthesis by activating the mammalian target of rapamycin (mTORC1). Increased muscle protein synthesis can lead to increased muscle mass, strength and function over time. This review aims to address the current recommended dietary allowance (RDA) for protein and whether or not this value meets the needs for older adults based upon current scientific evidence. The current RDA for protein is 0.8 g/kg body weight/day. However, literature suggests that consuming protein in amounts greater than the RDA can improve muscle mass, strength and function in older adults.

Effects of different doses of leucine ingestion following eight weeks of resistance exercise on protein synthesis and hypertrophy of skeletal muscle in rats

[Purpose]

This study was designed to determine the appropriate Leucine intake volume to obtain the effects of restoring damaged muscle through the synthesis of muscle proteins to increase skeletal muscle and improve exercise performance, and to achieve enhanced muscle hypertrophy.

[Methods]

To clarify the effects of leucine on skeletal muscle hypertrophy of SD rats, following eight weeks of resistance exercise (climbing ladder), the mass of the FHL (Flexor hallucis longus) was measured after extraction, after which change in the activity of muscle signaling proteins (PKB/Akt, mTOR, p70S6K, 4EBP1) was analyzed.

[Results]

The expressions of PKB/Akt, mTOR and p70S6K were increased in L5 (Leucine 50% administration group) compared with the control group (CON) and exercise group (Ex, exercise training group); EL1 (exercise + 10% leucine administration group) and EL5 (exercise + 50% Leucine administration) also exhibited increased expressions of PKB/Akt, mTOR, and p70S6K, while no difference between EL1 and EL5 were observed. No significant differences in 4EBP1 were found among any of the groups. In addition, there were no differences in FHL mass, while relative mass (FHL/body mass) was increased in the exercise group (Ex, EL1, EL5) compared with the control group. No differences were observed among the exercise groups.

[Conclusion]

The present study demonstrated that the relative body mass was increased in the EX group compared with the CON group, while no significant differences in muscle mass could be found among the groups. Even though some signaling proteins were increased, or some differences existed among groups, there were no differences in muscle mass between the leucine administration and exercise training combined with leucine administration groups in the present study.

The effects of 8 weeks of whey or rice protein supplementation on body composition and exercise performance

Background

Consumption of moderate amounts of animal-derived protein has been shown to differently influence skeletal muscle hypertrophy during resistance training when compared with nitrogenous and isoenergetic amounts of plant-based protein administered in small to moderate doses. Therefore, the purpose of the study was to determine if the post-exercise consumption of rice protein isolate could increase recovery and elicit adequate changes in body composition compared to equally dosed whey protein isolate if given in large, isocaloric doses.

Methods

24 college-aged, resistance trained males were recruited for this study. Subjects were randomly and equally divided into two groups, either consuming 48 g of rice or whey protein isolate (isocaloric and isonitrogenous) on training days. Subjects trained 3 days per week for 8 weeks as a part of a daily undulating periodized resistance-training program. The rice and whey protein supplements were consumed immediately following exercise. Ratings of perceived recovery, soreness, and readiness to train were recorded prior to and following the first training session. Ultrasonography determined muscle thickness, dual emission x-ray absorptiometry determined body composition, and bench press and leg press for upper and lower body strength were recorded during weeks 0, 4, and 8. An ANOVA model was used to measure group, time, and group by time interactions. If any main effects were observed, a Tukey post-hoc was employed to locate where differences occurred.

Results

No detectable differences were present in psychometric scores of perceived recovery, soreness, or readiness to train (p > 0.05). Significant time effects were observed in which lean body mass, muscle mass, strength and power all increased and fat mass decreased; however, no condition by time interactions were observed (p > 0.05).

Conclusion

Both whey and rice protein isolate administration post resistance exercise improved indices of body composition and exercise performance; however, there were no differences between the two groups.

The effects of soy and whey protein supplementation on acute hormonal reponses to resistance exercise in men

OBJECTIVE

For many resistance-trained men concerns exist regarding the production of estrogen with the consumption of soy protein when training for muscle strength and size. Thus, the purpose of this investigation was to examine the effects of soy and whey protein supplementation on sex hormones following an acute bout of heavy resistance exercise in resistance trained men.

METHODS

Ten resistance-trained men (age 21.7 ± 2.8 [SD] years; height 175.0 ± 5.4 cm; weight 84.2 ± 9.1 kg) volunteered to participate in an investigation. Utilizing a within subject randomized crossover balanced placebo design, all subjects completed 3 experimental treatment conditions supplementing with whey protein isolate (WPI), soy protein isolate (SPI), and maltodextrin placebo control for 14 days with participants ingesting 20 g of their assigned supplement each morning at approximately the same time each day. Following supplementation, subjects performed an acute heavy resistance exercise test consisting of 6 sets of 10 repetitions in the squat exercise at 80% of the subject's one repetition maximum.

RESULTS

This investigation observed lower testosterone responses following supplementation with soy protein in addition to a positive blunted cortisol response with the use of whey protein at some recovery time points. Although sex hormone binding globulin (SHBG) was proposed as a possible mechanism for understanding changes in androgen content, SHBG did not differ between experimental treatments. Importantly, there were no significant differences between groups in changes in estradiol concentrations.

CONCLUSION

Our main findings demonstrate that 14 days of supplementation with soy protein does appear to partially blunt serum testosterone. In addition, whey influences the response of cortisol following an acute bout of resistance exercise by blunting its increase during recovery. Protein supplementation alters the physiological responses to a commonly used exercise modality with some differences due to the type of protein utilized.

Antihypertensive effects of dietary protein and its mechanism

Hypertension is a leading cause of morbidity and mortality worldwide. Individuals with hypertension are at increased risk of stroke, heart disease and kidney failure. Both genetic and lifestyle factors, particularly diet, have been attributed an important role in the development of hypertension. Reducing dietary sugar and salt intake can help lower blood pressure; similarly, adequate protein intake may also attenuate hypertension. Observational, cross-sectional and longitudinal epidemiological studies, and controlled clinical trials, have documented significant inverse associations between protein intake and blood pressure. Human and animal studies have shown that specific amino acids within proteins may have antihypertensive effects. Cysteine, glutathione (a tripeptide), glutamate and arginine attenuate and prevent alterations that cause hypertension including insulin resistance, decreased nitric oxide bioavailability, altered renin angiotensin system function, increased oxidative stress and formation of advanced glycation end products. Leucine increases protein synthesis in skeletal muscle and improves insulin resistance by modulating hepatic gluconeogenesis. Taurine and tryptophan attenuate sympathetic nervous system activity. Soy protein helps lower blood pressure through its high arginine content and antioxidant activity exhibited by isoflavones. A diet containing an ample amount of protein may be a beneficial lifestyle choice for individuals with hypertension; one example is the Dietary Approaches to Stop Hypertension (DASH) diet, which is low in salt and saturated fat; includes whole grains, lean meat, poultry, fish and nuts; and is rich in vegetables, fruits and low-fat dairy products, which are good sources of antioxidant vitamins, minerals and fibre. Including an adequate supply of soy in the diet should also be encouraged.

Leucine supplementation chronically improves muscle protein synthesis in older adults consuming the RDA for protein

BACKGROUND & AIM

Protein-energy supplementation is routinely employed to combat muscle loss. However, success is often compromised by increased satiety, poor palatability, high costs and low compliance.

METHODS

For 2-weeks we supplemented meals of older individuals with leucine (4 g/meal; 3 meals/day; days 2-14). Metabolic studies were performed prior to (Day 1) and following (Day 15) supplementation. Leucine was not provided on metabolic study days. Venous blood and vastus lateralis muscle biopsies were obtained during a primed constant infusion of L-[ring-(13)C(6)] phenylalanine. Mixed muscle fractional synthesis rate (FSR), body composition and markers of nutrient signaling (mTOR, 4E-BP1 and p70S6K1 phosphorylation) were measured before and after a low protein/carbohydrate simulated meal.

RESULTS

The meal modestly increased FSR on Day 1 (postabsorptive: 0.063 ± 0.004 vs. postprandial: 0.075 ± 0.006%/h; p = 0.03), however, two weeks of leucine supplementation increased postabsorptive FSR (p = 0.004) and the response to the meal (p = 0.01) (postabsorptive: 0.074 ± 0.007 vs. postprandial: 0.10 ± 0.007%/h). Changes in FSR were mirrored by increased phosphorylation of mTOR, 4E-BP1 and p70S6K1 (p ≤ 0.1). No change in fat free mass was observed (p > 0.05).

CONCLUSIONS

In older adults, leucine supplementation may improve muscle protein synthesis in response to lower protein meals.

Nutritional recommendations for the management of sarcopenia

The Society for Sarcopenia, Cachexia, and Wasting Disease convened an expert panel to develop nutritional recommendations for prevention and management of sarcopenia. Exercise (both resistance and aerobic) in combination with adequate protein and energy intake is the key component of the prevention and management of sarcopenia. Adequate protein supplementation alone only slows loss of muscle mass. Adequate protein intake (leucine-enriched balanced amino acids and possibly creatine) may enhance muscle strength. Low 25(OH) vitamin D levels require vitamin D replacement.

Branched-chain amino acid supplementation increases the lactate threshold during an incremental exercise test in trained individuals

The effects of branched-chain amino acid (BCAA) supplementation on the lactate threshold (LT) were investigated as an index of endurance exercise capacity. Eight trained male subjects (21+/-2 y) participated in a double-blind crossover placebo-controlled study. The subjects were randomly assigned to two groups and were provided either a BCAA drink (0.4% BCAA, 4% carbohydrate; 1,500 mL/d) or an iso-caloric placebo drink for 6 d. On the 7th day, the subjects performed an incremental loading exercise test with a cycle ergometer until exhaustion in order to measure the LT. The test drink (500 mL) was ingested 15-min before the test. Oxygen consumption VO2 and the respiratory exchange ratio (RER) during the exercise test were measured with the breath-by-breath method. Blood samples were taken before and during the exercise test to measure the blood lactate and plasma BCAA concentrations. The same exercise test was performed again 1 wk later. BCAA supplementation increased the plasma BCAA concentration during the exercise test, while plasma BCAA concentration decreased in the placebo trial. The RER during the exercise test in the BCAA trial was lower than that in the placebo trial (p<0.05). The VO2 and workload levels at LT point in the BCAA trial were higher than those in the placebo trial (VO2: 29.8+/-6.8 vs. 26.4+/-5.4 mL/kg/min; workload: 175+/-42 vs. 165+/-38 W, p<0.05, respectively). The VO2max in the BCAA trial was higher than that in the placebo trial (47.1+/-5.7 vs. 45.2+/-5.0 mL/kg/min, p<0.05). These results suggest that BCAA supplementation may be effective to increase the endurance exercise capacity.

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.

Cerebrospinal fluid concentrations of large neutral and basic amino acids in Macaca mulatta: diurnal variations and responses to chronic changes in dietary protein intake

In rats, dietary protein intake influences brain concentrations of tryptophan, tyrosine, and other large neutral amino acids (LNAAs) and the neurotransmitters to which they are linked. Few experiments have examined these dietary protein-amino acid relationships in nonhuman primates, in relation to time of day or dietary protein content. We therefore examined the effect in monkeys of changes in chronic protein intake on 24-hour plasma and cerebrospinal fluid (CSF) concentrations of LNAAs (tyrosine, phenylalanine, branched-chain amino acids) and basic amino acids. Juvenile male monkeys (Macaca mulatta) consumed for sequential 4-week periods diets differing in protein content (approximately 23% --> approximately 16% --> approximately 10% --> approximately 6% protein [percentage of energy]). The daily ration was presented as a morning meal of fruit and an afternoon meal of fruit and a commercial diet to mimic feeding patterns in the wild. During week 4 on each diet, blood and CSF were sampled repeatedly over a 48-hour period via indwelling catheters. Plasma and CSF LNAA concentrations varied markedly with time of day and dietary protein content, showing up to 4-fold variations. Diurnal variations in plasma and CSF basic amino acids were smaller in magnitude and generally not strongly linked to dietary protein content. A measure of the competitive transport of LNAAs across the blood-brain barrier, calculated using plasma concentrations of the LNAAs and their blood-brain barrier kinetic constants, predicted the observed CSF concentration of each LNAA examined remarkably well, except for phenylalanine. Based on observations in rats, the variations in the CSF concentrations of the LNAAs in monkeys may be large enough to influence metabolic and signaling pathways in brain to which they have been linked.

Protein supplementation may enhance the spontaneous recovery of neurological alterations in patients with ischaemic stroke

Objective: To determine whether protein supplementation could enhance neurological recovery in subacute patients with ischaemic stroke.

Design: Alimentation-independent patients with ischaemic stroke were randomly allocated to either 21 days of protein supplementation (protein-supplemented group; n=20) or to a spontaneous diet only (control group; n=21) in order to investigate the recovery of neurological changes (measured using the National Institute of Health (NIH) Stroke Scale).

Setting: Tertiary care rehabilitation in Italy.

Participants: Forty-two patients (27 male and 15 female; 66.4 ± 11 years) 16 ±2 days after the acute event.

Intervention: Supplementation with a hyperproteic nutritional formula (10% protein).

Main outcome measures: NIH Stroke Scale and protein intake.

Results: At admission to rehabilitation, both groups of patients were homogeneous for demographic, clinical and functional characteristics. After 21 days from the start of the protocol, the NIH Stroke Scale was found to be enhanced in the group with supplemental proteins (-4.4 ± 1.5 score versus -3 ± 1.4 of control group; P<0.01). When expressed as difference (▵) between baseline and 21 days, the NIH Stroke Scale correlated negatively with change in protein intake (g/day) (r=-0.50, P= 0.001) and positively with change in carbohydrate/protein ratio (r=+0.40, P=0.01)

Conclusions: Protein supplementation may enhance neurological recovery in subacute patients with ischaemic stroke.

Branched-chain amino acids may improve recovery from a vegetative or minimally conscious state in patients with traumatic brain injury: a pilot study

OBJECTIVE

To investigate whether supplementation with branched-chain amino acids (BCAAs) may improve recovery of patients with a posttraumatic vegetative or minimally conscious state.

DESIGN

Patients were randomly assigned to 15 days of intravenous BCAA supplementation (n=22; 19.6g/d) or an isonitrogenous placebo (n=19).

SETTING

Tertiary care rehabilitation setting.

PARTICIPANTS

Patients (N=41; 29 men, 12 women; mean age, 49.5+/-21 y) with a posttraumatic vegetative or minimally conscious state, 47+/-24 days after the index traumatic event.

INTERVENTION

Supplementation with BCAAs.

MAIN OUTCOME MEASURE

Disability Rating Scale (DRS) as log(10)DRS.

RESULTS

Fifteen days after admission to the rehabilitation department, the log(10)DRS score improved significantly only in patients who had received BCAAs (log(10)DRS score, 1.365+/-0.08 to 1.294+/-0.05; P<.001), while the log(10)DRS score in the placebo recipients remained virtually unchanged (log(10)DRS score, 1.373+/-0.03 to 1.37+/-0.03; P not significant). The difference in improvement of log(10)DRS score between the 2 groups was highly significant (P<.000). Moreover, 68.2% (n=15) of treated patients achieved a log(10)DRS point score of .477 or higher (3 as geometric mean) that allowed them to exit the vegetative or minimally conscious state.

CONCLUSIONS

Supplemented BCAAs may improve the recovery from a vegetative or minimally conscious state in patients with posttraumatic vegetative or minimally conscious state.

Effects of branched-chain amino acids supplementation on physiological and psychological performance during an offshore sailing race

The aim of the present study was to investigate the effect of protein diets, rich in branched chain amino acids (BCAA) on perceived exertion, mental and physical performance during an offshore sailing race that lasted 32 h. Twelve sailors were randomly allocated into one of two groups [Control (CON) and BCAA: n = 6/group]. The BCAA group consumed a standard diet of 11.2 MJ day(-1) (58% carbohydrate, 30% fat, 12% Protein) along with a high-protein supplement of 1.7 MJ day(-1) (40% carbohydrate, 35% protein, 25% fat) and 1.7 MJ day(-1) composed of 50% valine, 35% leucine, and 15% isoleucine. CON was given a standard diet of 14.5 MJ day(-1) (58% carbohydrate, 30% fat and 12% protein). During the race, heart rate was monitored. Subjects self-evaluated their feeling of fatigue every 3 h, and 12 samples of saliva from each subject were collected to perform cortisol assays. Before and after the race a vertical jump and a handgrip test were performed, and mental performance was evaluated with a standardized battery of tests. A significant increase in the feeling of fatigue was noted on the second day (D2) of race in both groups; the increase was higher in CON (P < 0.05). For both groups, salivary cortisol concentration followed a nycthemeral rhythm, with an alteration during the race as evidenced by high midnight cortisol levels between D1 and D2, and significantly decreased cortisol levels observed on D2 (P < 0.05). There was no change in physical performance at the end of the race in both groups. As a significant decrease (P < 0.05) in short-term memory performance was observed only in the CON group. These data indicate that an offshore sailing race enhances the feeling of fatigue, and decreases short-term memory performance. These detrimental consequences are reduced by a high-protein diet with BCAA.

Protein and overtraining: potential applications for free-living athletes

Despite a more than adequate protein intake in the general population, athletes have special needs and situations that bring it to the forefront. Overtraining is one example. Hard-training athletes are different from sedentary persons from the sub-cellular to whole-organism level. Moreover, competitive, "free-living" (less-monitored) athletes often encounter negative energy balance, sub-optimal dietary variety, injuries, endocrine exacerbations and immune depression. These factors, coupled with "two-a-day" practices and in-season demands require that protein not be dismissed as automatically adequate or worse, deleterious to health. When applying research to practice settings, one should consider methodological aspects such as population specificity and control variables such as energy balance. This review will address data pertinent to the topic of athletic protein needs, particularly from a standpoint of overtraining and soft tissue recovery. Research-driven strategies for adjusting nutrition and exercise assessments will be offered for consideration. Potentially helpful nutrition interventions for preventing and treating training complications will also be presented.

Leucine regulates translation initiation of protein synthesis in skeletal muscle after exercise

High-performance physical activity and postexercise recovery lead to significant changes in amino acid and protein metabolism in skeletal muscle. Central to these changes is an increase in the metabolism of the BCAA leucine. During exercise, muscle protein synthesis decreases together with a net increase in protein degradation and stimulation of BCAA oxidation. The decrease in protein synthesis is associated with inhibition of translation initiation factors 4E and 4G and ribosomal protein S6 under regulatory controls of intracellular insulin signaling and leucine concentrations. BCAA oxidation increases through activation of the branched-chain alpha-keto acid dehydrogenase (BCKDH). BCKDH activity increases with exercise, reducing plasma and intracellular leucine concentrations. After exercise, recovery of muscle protein synthesis requires dietary protein or BCAA to increase tissue levels of leucine in order to release the inhibition of the initiation factor 4 complex through activation of the protein kinase mammalian target of rapamycin (mTOR). Leucine's effect on mTOR is synergistic with insulin via the phosphoinositol 3-kinase signaling pathway. Together, insulin and leucine allow skeletal muscle to coordinate protein synthesis with physiological state and dietary intake.

Branched-chain amino acids activate key enzymes in protein synthesis after physical exercise

BCAAs (leucine, isoleucine, and valine), particularly leucine, have anabolic effects on protein metabolism by increasing the rate of protein synthesis and decreasing the rate of protein degradation in resting human muscle. Also, during recovery from endurance exercise, BCAAs were found to have anabolic effects in human muscle. These effects are likely to be mediated through changes in signaling pathways controlling protein synthesis. This involves phosphorylation of the mammalian target of rapamycin (mTOR) and sequential activation of 70-kD S6 protein kinase (p70 S6 kinase) and the eukaryotic initiation factor 4E-binding protein 1. Activation of p70 S6 kinase, and subsequent phopsphorylation of the ribosomal protein S6, is associated with enhanced translation of specific mRNAs. When BCAAs were supplied to subjects during and after one session of quadriceps muscle resistance exercise, an increase in mTOR, p70 S6 kinase, and S6 phosphorylation was found in the recovery period after the exercise with no effect of BCAAs on Akt or glycogen synthase kinase 3 (GSK-3) phosphorylation. Exercise without BCAA intake led to a partial phosphorylation of p70 S6 kinase without activating the enzyme, a decrease in Akt phosphorylation, and no change in GSK-3. It has previously been shown that leucine infusion increases p70 S6 kinase phosphorylation in an Akt-independent manner in resting subjects; however, a relation between mTOR and p70 S6 kinase has not been reported previously. The results suggest that BCAAs activate mTOR and p70 S6 kinase in human muscle in the recovery period after exercise and that GSK-3 is not involved in the anabolic action of BCAAs on human muscle.

Effects of dietary leucine supplementation on exercise performance

Branched chain amino acids (BCAA), particularly leucine, have been suggested to be ergogenic for both endurance and strength/power performance. This study investigated the effects of dietary leucine supplementation on the exercise performance of outrigger canoeists. Thirteen (ten female, three male) competitive outrigger canoeists [aged 31.6 (2.2) year, VO(2max) 47.1 (2.0) ml kg(-1) min(-1)] underwent testing before and after 6-week supplementation with either capsulated L: -leucine (45 mg kg(-1) d(-1); n = 6) or placebo (cornflour; n = 7). Testing included anthropometry, 10 s upper body power and work and a row to exhaustion at 70-75% maximal aerobic power where perceived exertion (RPE), heart rate (HR) and plasma BCAA and tryptophan concentrations were assessed. Leucine supplementation resulted in significant increases in plasma leucine and total BCAA concentrations. Upper body power and work significantly increased in both groups after supplementation but power was significantly greater after leucine supplementation compared to the placebo [6.7 (0.7) v. 6.0 (0.7) W kg(-1)]. Rowing time significantly increased [77.6 (6.3)-88.3 (7.3) min] and average RPE significantly decreased [14.5 (1.5)-12.9 (1.4)] with leucine supplementation while these variables were unchanged with the placebo. Leucine supplementation had no effect on the plasma tryptophan to BCAA ratio, HR or anthropometric variables. Six weeks' dietary leucine supplementation significantly improved endurance performance and upper body power in outrigger canoeists without significant change in the plasma ratio of tryptophan to BCAA.

Ingesta de calcio y obesidad

Recent evidences from epidemiological and intervention trials suggest that a higher calcium intake is associated with a lower body weight and a reduction in total and central body fat. The potential role of calcium intake in the regulation of body adiposity has been explained by the intracellular calcium, which is able to promote adipocyte fat accumulation by exerting a coordinate regulation stimulating lipogenesis and suppressing lipolysis. Moreover, the intracellular calcium has been implicated on the etiopathogenesis of hypertension, insulin resistance and dyslipidemia, appearing as a potential common substrate in the metabolic syndrome. Dietary modulation of intracellular calcium through calciotropic hormones opens an exciting possibility to prevent and tackle obesity and its associated complications by increasing the calcium intake. However, available evidences are mostly indirect and further studies specifically designed for this purpose are needed.

Dietary protein impact on glycemic control during weight loss

Diets with higher protein (1.5 g x kg(-1) x d(-1)) and reduced carbohydrates (120 to 200 g/d) appear to enhance weight loss due to a higher loss of body fat and reduced loss of lean body mass. While studies of prolonged use of moderate protein diets are not available, short-term studies report beneficial effects associated with increased satiety, increased thermogenesis, sparing of muscle protein loss, and enhanced glycemic control. Combined impacts of a moderate protein diet are likely derived from lower carbohydrates resulting in lower postprandial increase in blood glucose and lower insulin response, and higher protein providing increased BCAA leucine levels and gluconeogenic substrates. A key element in the diet appears to be the higher intake of BCAA leucine with unique regulatory actions on muscle protein synthesis, modulation of the insulin signal, and sparing of glucose use by stimulation of the glucose-alanine cycle. This review focuses on the contributions of leucine and the BCAA to regulation of muscle protein synthesis and glycemic control.

Increased dietary protein modifies glucose and insulin homeostasis in adult women during weight loss

Amino acids interact with glucose metabolism both as carbon substrates and by recycling glucose carbon via alanine and glutamine; however, the effect of protein intake on glucose homeostasis during weight loss remains unknown. This study tests the hypothesis that a moderate increase in dietary protein with a corresponding reduction of carbohydrates (CHO) stabilizes fasting and postprandial blood glucose and insulin during weight loss. Adult women (n = 24; >15% above ideal body weight) were assigned to either a Protein Group [protein: 1.6 g/(kg. d); CHO <40% of energy] or CHO Group [protein: 0.8 g/(kg. d); CHO >55%]. Diets were equal in energy (7100 kJ/d) and fat (50 g/d). After 10 wk, the Protein Group lost 7.53 +/- 1.44 kg and the CHO Group lost 6.96 +/- 1.36 kg. Plasma amino acids, glucose and insulin were determined after a 12-h fast and 2 h after a 1.67 MJ test meal containing either 39 g CHO, 33 g protein and 13 g fat (Protein Group) or 57 g CHO, 12 g protein and 14 g fat (CHO Group). After 10 wk, subjects in the CHO Group had lower fasting (4.34 +/- 0.10 vs 4.89 +/- 0.11 mmol/L) and postprandial blood glucose (3.77 +/- 0.14 vs. 4.33 +/- 0.15 mmol/L) and an elevated insulin response to meals (207 +/- 21 vs. 75 +/- 18 pmol/L). This study demonstrates that consumption of a diet with increased protein and a reduced CHO/protein ratio stabilizes blood glucose during nonabsorptive periods and reduces the postprandial insulin response.

The role of leucine in weight loss diets and glucose homeostasis

Debate about the optimum balance of macronutrients for adult weight maintenance or weight loss continues to expand. Often this debate centers on the relative merits or risks of carbohydrates vs. fats; however, there is increasing interest in the optimal level of dietary protein for weight loss. Diets with a reduced ratio of carbohydrates/protein are reported to be beneficial for weight loss, although diet studies appear to lack a fundamental hypothesis to support higher protein intakes. Presently, needs for dietary proteins are established by the recommended daily allowance (RDA) as the minimum level of protein necessary to maintain nitrogen balance. The RDA define the primary use of amino acids as substrates for synthesis of body proteins. There is emerging evidence that additional metabolic roles for some amino acids require plasma and intracellular levels above minimum needs for protein synthesis. The branched-chain amino acid leucine is an example of an amino acid with numerous metabolic roles that function in proportion with cellular concentration. This review provides an overview of the current understanding of metabolic roles of leucine and proposes a metabolic framework to evaluate the merits of a higher protein diet for weight loss.