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

Dietary protein and amino acid intakes for mitigating sarcopenia in humans

Adult humans generally experience a 0.5-1%/year loss in whole-body skeletal muscle mass and a reduction of muscle strength by 1.5-5%/year beginning at the age of 50 years. This results in sarcopenia (aging-related progressive losses of skeletal muscle mass and strength) that affects 10-16% of adults aged ≥ 60 years worldwide. Concentrations of some amino acids (AAs) such as branched-chain AAs, arginine, glutamine, glycine, and serine are reduced in the plasma of older than young adults likely due to insufficient protein intake, reduced protein digestibility, and increased AA catabolism by the portal-drained viscera. Acute, short-term, or long-term administration of some of these AAs or a mixture of proteinogenic AAs can enhance blood flow to skeletal muscle, activate the mechanistic target of rapamycin cell signaling pathway for the initiation of muscle protein synthesis, and modulate the metabolic activity of the muscle. In addition, some AA metabolites such as taurine, β-alanine, carnosine, and creatine have similar physiological effects on improving muscle mass and function in older adults. Long-term adequate intakes of protein and the AA metabolites can aid in mitigating sarcopenia in elderly adults. Appropriate combinations of animal- and plant-sourced foods are most desirable to maintain proper dietary AA balance.

Untargeted metabolomic profiling of serum from client-owned cats with early and late-stage chronic kidney disease

Evaluation of the metabolome could discover novel biomarkers of disease. To date, characterization of the serum metabolome of client-owned cats with chronic kidney disease (CKD), which shares numerous pathophysiological similarities to human CKD, has not been reported. CKD is a leading cause of feline morbidity and mortality, which can be lessened with early detection and appropriate treatment. Consequently, there is an urgent need for early-CKD biomarkers. The goal of this cross-sectional, prospective study was to characterize the global, non-targeted serum metabolome of cats with early versus late-stage CKD compared to healthy cats. Analysis revealed distinct separation of the serum metabolome between healthy cats, early-stage and late-stage CKD. Differentially abundant lipid and amino acid metabolites were the primary contributors to these differences and included metabolites central to the metabolism of fatty acids, essential amino acids and uremic toxins. Correlation of multiple lipid and amino acid metabolites with clinical metadata important to CKD monitoring and patient treatment (e.g. creatinine, muscle condition score) further illustrates the relevance of exploring these metabolite classes further for their capacity to serve as biomarkers of early CKD detection in both feline and human populations.

Amino acid-stimulated insulin secretion: a path forward in type 2 diabetes

Qualitative and quantitatively appropriate insulin secretion is essential for optimal control of blood glucose. Beta-cells of the pancreas produce and secrete insulin in response to glucose and non-glucose stimuli including amino acids. In this manuscript, we review the literature on amino acid-stimulated insulin secretion in oral and intravenous in vivo studies, in addition to the in vitro literature, and describe areas of consensus and gaps in understanding. We find promising evidence that the synergism of amino acid-stimulated insulin secretion could be exploited to develop novel therapeutics, but that a systematic approach to investigating these lines of evidence is lacking. We highlight evidence that supports the relative preservation of amino acid-stimulated insulin secretion compared to glucose-stimulated insulin secretion in type 2 diabetes, and make the case for the therapeutic potential of amino acids. Finally, we make recommendations for research and describe the potential clinical utility of nutrient-based treatments for type 2 diabetes including remission services.

Integrated analysis of transcriptome and proteome for exploring mechanism of promoting proliferation of equine satellite cells associated with leucine

The proliferation and differentiation of skeletal muscle satellite cells (SCs) are necessary for the development of mature skeletal muscle. Leucine (Leu) is both an essential amino acid (EAA) and a branched-chain amino acid (BCAA), which has attracted worldwide attention due to its ability to repair and become new fibers. We separated the equine SCs into the control group (CON) and the Leu-supplemented group (LEU), which the cells were cultured in Leu-deprived and Leu-supplemented media respectively. We combined the transcriptome (RNA-Seq) and quantitative proteome (TMT) profiling analyses on proliferation of equine SCs associated with Leu. 1839 up-regulated and 631 down-regulated genes made up the 2470 differentially expressed genes (DEGs), and the 253 differentially abundant proteins (DEPs) included 118 up-regulated and 135 down-regulated proteins. 110 overlapping genes were verified based on the mRNA and protein translation relationship. Moreover, by comparing overlapped pathways through enrichment analysis, we found 13 genes not only appeared among 110 key DEGs/DEPs but also enriched in the KEGG overlapping signaling pathway, including CCL26, STAT2, PCK2, ASNS, GPT2, SHMT2, PHGDH, PGAM2, PSAT1, FTL, HMOX1, STEAP1 and STEAP2. To our knowledge, this is the first report in the world to systematically show how Leu regulated the growth of equine SCs. Leu deficiency inhibits the proliferation of equine SCs and development of fresh muscle fibers was proved in this paper. The main genes in charge of the Leu-induced proliferation of horse SCs have been found. These genes will make it easier to understand the mechanism at work and offer new information for enhancing the performance of sport horses and alleviating the equine muscle damage during exercise in the future.

Loss of Muscle Mass and Strength After Hip Fracture: an Intervention Target for Nutrition Supplementation

PURPOSEOF REVIEW

To summarize what is known about the deleterious effect of hip fracture on muscle mass and strength as well as the scientific evidence for post-surgical nutrition supplementation to maintain muscle and improve function.

RECENT FINDINGS

This review provides a discussion of the relationship between muscle mass, strength, and physical function following hip fracture, briefly describes the approaches to measuring lean mass, discusses prevalence of sarcopenia and malnutrition among older men and women with hip fracture, and reviews the effects of essential amino acids on muscle. Loss of muscle mass and strength following hip fracture is substantial with consequences for recovery of functional independence. EAA-based nutrition supplementation, which directly effects muscle, has potential to improve outcomes.

Nutritional Interventions: Dietary Protein Needs and Influences on Skeletal Muscle of Older Adults

BACKGROUND

This narrative review describes foundational and emerging evidence of how dietary protein intakes may influence muscle-related attributes of older adults.

METHODS

PubMed was used to identify pertinent research.

RESULTS

Among medically stable older adults, protein intakes below the recommended dietary allowance (RDA) (0.8 g/kg body weight [BW]/d) exacerbate age-related reductions in muscle size, quality, and function. Dietary patterns with total protein intakes at or moderately above the RDA, including one or preferably more meals containing sufficient dietary protein to maximize protein anabolism, promote muscle size and function. Some observational studies suggest protein intakes from 1.0 to 1.6 g/kg BW/d may promote greater muscle strength and function more so than muscle size. Experimental findings from randomized controlled feeding trials indicate protein intakes greater than the RDA (averaging ~1.3 g/kg BW/d) do not influence indices of lean body mass or muscle and physical functions with non-stressed conditions, but positively influence changes in lean body mass with purposeful catabolic (energy restriction) or anabolic (resistance exercise training) stressors. Among older adults with diagnosed medical conditions or acute illness, specialized protein or amino acid supplements that stimulate muscle protein synthesis and improve protein nutritional status may attenuate the loss of muscle mass and function and improve survival of malnourished patients. Observational studies favor animal versus plant protein sources for sarcopenia-related parameters.

CONCLUSIONS

Quantity, quality, and patterning of dietary protein consumed by older adults with varied metabolic states, and hormonal and health status influence the nutritional needs and therapeutic use of protein to support muscle size and function.

Age-related muscle anabolic resistance: inevitable or preventable?

Age-related loss of muscle mass, strength, and performance, commonly referred to as sarcopenia, has wide-ranging detrimental effects on human health, the ramifications of which can have serious implications for both morbidity and mortality. Various interventional strategies have been proposed to counteract sarcopenia, with a particular emphasis on those employing a combination of exercise and nutrition. However, the efficacy of these interventions can be confounded by an age-related blunting of the muscle protein synthesis response to a given dose of protein/amino acids, which has been termed "anabolic resistance." While the pathophysiology of sarcopenia is undoubtedly complex, anabolic resistance is implicated in the progression of age-related muscle loss and its underlying complications. Several mechanisms have been proposed as underlying age-related impairments in the anabolic response to protein consumption. These include decreased anabolic molecular signaling activity, reduced insulin-mediated capillary recruitment (thus, reduced amino acid delivery), and increased splanchnic retention of amino acids (thus, reduced availability for muscular uptake). Obesity and sedentarism can exacerbate, or at least facilitate, anabolic resistance, mediated in part by insulin resistance and systemic inflammation. This narrative review addresses the key factors and contextual elements involved in reduction of the acute muscle protein synthesis response associated with aging and its varied consequences. Practical interventions focused on dietary protein manipulation are proposed to prevent the onset of anabolic resistance and mitigate its progression.

Potential mechanisms involved in regulating muscle protein turnover after acute exercise: A brief review

It is well established that resistance training increases muscle mass. Indeed, there is evidence to suggest that a single session of resistance training is associated with an increase in muscle protein synthesis in young adults. However, the fundamental mechanisms that are involved in regulating muscle protein turnover rates after an acute bout of physical exercise are unclear. Therefore, this review will briefly focus on summarizing the potential mechanisms behind the growth of skeletal muscle after physical exercise. We also present mechanistic differences that may exist between young and older individuals during muscle protein synthesis and breakdown after physical exercise. Pathways leading to the activation of AKT/mTOR signals after resistance exercise and the activation of AMPK signaling pathway following a HIIT (High intensity interval training) are discussed.

A Transcriptomic Regulatory Network among miRNAs, lncRNAs, circRNAs, and mRNAs Associated with L-leucine-induced Proliferation of Equine Satellite Cells

In response to muscle injury, muscle stem cells are stimulated by environmental signals to integrate into damaged tissue to mediate regeneration. L-leucine (L-leu), a branched-chain amino acid (BCAA) that belongs to the essential amino acids (AAs) of the animal, has gained global interest on account of its muscle-building and regenerating effects. The present study was designed to investigate the impact of L-leu exposure to promote the proliferation of equine skeletal muscle satellite cells (SCs) on the regulation of RNA networks, including mRNA, long non-coding RNA (lncRNA), covalently closed circular RNA (circRNA), and microRNA (miRNA) in skeletal muscles. Equine SCs were used as a cell model and cultured in different concentrations of L-leu medium. The cell proliferation assay found that the optimal concentration of L-leu was 2 mM, so we selected cells cultured with L-leu concentrations of 0 mM and 2 mM for whole-transcriptiome sequencing, respectively. By high-throughput sequencing analysis, 2470 differentially expressed mRNAs (dif-mRNAs), 363 differentially expressed lncRNAs (dif-lncRNAs), 634 differentially expressed circRNAs (dif-circRNAs), and 49 differentially expressed miRNAs (dif-miRNAs) were significantly altered in equine SCs treated with L-leu. To identify the function of autoimmunity and anti-inflammatory responses after L-leu exposure, enrichment analysis was conducted on those differentially expressed genes (DEGs) related to lncRNA, circRNA, and miRNA. The hub genes were selected from PPI Network, including ACACB, HMGCR, IDI1, HAO1, SHMT2, PSPH, PSAT1, ASS1, PHGDH, MTHFD2, and DPYD, and were further identified as candidate biomarkers to regulate the L-leu-induced proliferation of equine SCs. The up-regulated novel 699_star, down-regulated novel 170_star, and novel 360_mature were significantly involved in the competing endogenous RNA (ceRNA) complex network. The hub genes involved in cell metabolism and dif-miRNAs may play fundamental roles in the L-leu-induced proliferation of equine SCs. Our findings suggested that the potential network regulation of miRNAs, circ-RNAs, lncRNAs, and mRNAs plays an important role in the proliferation of equine SCs, so as to build up new perspectives on improving equine performance and treatment strategies for the muscle injuries of horses.

Effectiveness of a Novel Food Composed of Leucine, Omega-3 Fatty Acids and Probiotic Lactobacillus paracasei PS23 for the Treatment of Sarcopenia in Elderly Subjects: A 2-Month Randomized Double-Blind Placebo-Controlled Trial

Sarcopenia is a complex process characterized by a progressive decrease in muscle mass and strength. Various nutrients have been shown to be effective in supporting muscular performance. This randomized clinical trial aimed to evaluate the effectiveness of a 2-month administration of food for special medical purposes composed of omega-3 fatty acids (500 mg), leucine (2.5 g), and probiotic Lactobacillus paracasei PS23 (LPPS23), on appendicular lean mass (ALM), muscle performance, inflammatory status, and amino acid profile in sarcopenic patients. A total of 60 participants (aged 79.7 ± 4.8 years and a body mass index of 22.2 ± 2.1 kg/m2) were enrolled and randomly assigned to either intervention (n = 22) or placebo group (n = 28). Comparing the differences in effects between groups (intervention minus placebo effects), ALM increased significantly in the intervention group (p < 0.05), with no discernible change in the placebo group. Similarly, significant differences were also observed for the Tinetti scale (+2.39 points, p < 0.05), the SPPB total score (+2.22 points, p < 0.05), and the handgrip strength (4.09 kg, p < 0.05). Visceral adipose tissue significantly decreased in the intervention group compared to the placebo group at 60 days −0.69 g (95% CI: −1.09, 0.29) vs. 0.27 g (95% CI: −0.11, 0.65), groups difference −0.96 (95% CI: −1.52, 0.39, p = 0.001). A statistically significant increase in levels of valine, leucine, isoleucine, and total amino acid profiles was observed in the intervention group compared with the placebo group at 60 days (p = 0.001). When taken together, these beneficial effects may be attributed to the innovative composition of this special medical-purpose food which could be considered for the treatment of sarcopenia in the elderly.

Branched-Chain Amino Acids and Mitochondrial Biogenesis: An Overview and Mechanistic Summary

Branched-chain amino acids (BCAA) are essential in the diet and promote several vital cell responses which may have benefits for health and athletic performance, as well as disease prevention. While BCAA are well-known for their ability to stimulate muscle protein synthesis, their effects on cell energetics are also becoming well-documented, but these receive less attention. In this review, much of the current evidence demonstrating BCAA ability (as individual amino acids or as part of dietary mixtures) to alter regulators of cellular energetics with an emphasis on mitochondrial biogenesis and related signaling is highlighted. Several studies have shown, both in vitro and in vivo, that BCAA (either individual or as a mixture) may promote signaling associated with increased mitochondrial biogenesis including the upregulation of master regulator of mitochondrial biogenesis peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), as well as numerous downstream targets and related function. However, sparse data in humans and the difficulty of controlling variables associated with feeding studies leave the physiological relevance of these findings unclear. Future well-controlled diet studies will be needed to assess if BCAA consumption is associated with increased mitochondrial biogenesis and improved metabolic outcomes in healthy and/or diseased human populations.

The Effect of Leucine Supplementation on Sarcopenia-Related Measures in Older Adults: A Systematic Review and Meta-Analysis of 17 Randomized Controlled Trials

Background

The role of leucine in sarcopenia prevention remains unclear. We aimed to summarize the published data from randomized controlled trials (RCTs) to estimate the effect of leucine supplementation on sarcopenia-related measures in older adults.

Methods

A systematic literature search was performed using the electronic databases PubMed, Embase, and Web of Science with restriction to randomized controlled trials design from January 1, 2009 to March 19, 2022. Sarcopenia-related measures included handgrip strength, total lean mass, gait speed, leg press, 6-min walk test, short-physical performance battery, timed up-and-go test and 30-s chair-stand test. Fixed- and random-effects meta-analysis models were used to generate pooled weighted mean differences (WMDs) and 95% CIs. Heterogeneity was examined in subgroup and sensitivity analyses. Publication bias assessments were performed.

Results

A total of 17 RCTs enrolling 1418 subjects were identified. Leucine-isolated supplementation showed no effect on total lean mass (WMD = 0.03 kg, 95% CI: –0.51, 0.57, P = 0.917), handgrip strength (WMD = 1.23 kg, 95% CI: –0.58, 3.03, P = 0.183) and leg press (WMD = –1.35 kg, 95% CI: –7.46, 4.77, P = 0.666). However, leucine-combined supplementation including vitamin D showed a significant improvement in handgrip strength (WMD = 2.17 kg, 95% CI: 0.24, 4.10, P = 0.027) and gait speed (WMD = 0.03 m/s, 95% CI: 0.01, 0.05, P = 0.008).

Conclusion

Leucine-isolated supplementation did not improve muscle mass and strength in elderly. However, leucine-combined supplementation including vitamin D exhibited a significant benefit for muscle strength and performance including handgrip strength and gait speed in older adults. A combination of nutritional supplements would be a viable option for improving sarcopenia.

Effect of perindopril or leucine on physical performance in older people with sarcopenia: the LACE randomized controlled trial

BACKGROUND

This trial aimed to determine the efficacy of leucine and/or perindopril in improving physical function in older people with sarcopenia.

METHODS

Placebo-controlled, parallel group, double-blind, randomized two-by-two factorial trial. We recruited adults aged ≥ 70 years with sarcopenia, defined as low gait speed (<0.8 m/s on 4 m walk) and/or low handgrip strength (women < 20 kg, men < 30 kg) plus low muscle mass (using sex and body mass index category-specific thresholds derived from normative UK BioBank data) from 14 UK centres. Eligible participants were randomized to perindopril 4 mg or placebo, and to oral leucine powder 2.5 g or placebo thrice daily. The primary outcome was the between-group difference in the short physical performance battery (SPPB) score over 12-month follow-up by repeated-measures mixed models. Results were combined with existing systematic reviews using random-effects meta-analysis to derive summary estimates of treatment efficacy.

RESULTS

We screened 320 people and randomized 145 participants compared with an original target of 440 participants. For perindopril [n = 73, mean age 79 (SD 6), female sex 39 (53%), mean SPPB 7.1 (SD 2.3)] versus no perindopril [n = 72, mean age 79 (SD 6), female sex 39 (54%), mean SPPB 6.9 (SD 2.4)], median adherence to perindopril was lower (76% vs. 96%; P < 0.001). Perindopril did not improve the primary outcome [adjusted treatment effect -0.1 points (95%CI -1.2 to 1.0), P = 0.89]. No significant treatment benefit was seen for any secondary outcome including muscle mass [adjusted treatment effect -0.4 kg (95%CI -1.1 to 0.3), P = 0.27]. More adverse events occurred in the perindopril group (218 vs. 165), but falls rates were similar. For leucine [n = 72, mean age 78 (SD 6), female sex 38 (53%), mean SPPB 7.0 (SD 2.1)] versus no leucine [n = 72, mean age 79 (SD 6), female sex 40 (55%), mean SPPB 7.0 (SD 2.5)], median adherence was the same in both groups (76% vs. 76%; P = 0.99). Leucine did not improve the primary outcome [adjusted treatment effect 0.1 point (95%CI -1.0 to 1.1), P = 0.90]. No significant treatment benefit was seen for any secondary outcome including muscle mass [adjusted treatment effect -0.3 kg (95%CI -1.0 to 0.4), P = 0.47]. Meta-analysis of angiotensin converting enzyme inhibitor/angiotensin receptor blocker trials showed no clinically important treatment effect for the SPPB [between-group difference -0.1 points (95%CI -0.4 to 0.2)].

CONCLUSIONS

Neither perindopril nor leucine improved physical performance or muscle mass in this trial; meta-analysis did not find evidence of efficacy of either ACE inhibitors or leucine as treatments to improve physical performance.

Effect of High-Protein Diets on Integrated Myofibrillar Protein Synthesis before Anterior Cruciate Ligament Reconstruction: A Randomized Controlled Pilot Study

Increasing dietary protein intake during periods of muscle disuse may mitigate the resulting decline in muscle protein synthesis (MPS). The purpose of this randomized pilot study was to determine the effect of increased protein intake during periods of disuse before anterior cruciate ligament (ACL) reconstruction on myofibrillar protein synthesis (MyoPS), and proteolytic and myogenic gene expression. Six healthy, young males (30 ± 9 y) were randomized to consume a high-quality, optimal protein diet (OP; 1.9 g·kg−1·d−1) or adequate protein diet (AP; 1.2 g·kg−1·d−1) for two weeks before ACL reconstruction. Muscle biopsies collected during surgery were used to measure integrated MyoPS during the intervention (via daily deuterium oxide ingestion) and gene expression at the time of surgery. MyoPS tended to be higher, with a large effect size in OP compared to AP (0.71 ± 0.1 and 0.54 ± 0.1%·d−1; p = 0.076; g = 1.56). Markers of proteolysis and myogenesis were not different between groups (p > 0.05); however, participants with greater MyoPS exhibited lower levels of MuRF1 gene expression compared to those with lower MyoPS (r = −0.82, p = 0.047). The data from this pilot study reveal a potential stimulatory effect of increased daily protein intake on MyoPS during injury-mediated disuse conditions that warrants further investigation.

L-Carnitine Combined with Leucine Supplementation Does Not Improve the Effectiveness of Progressive Resistance Training in Healthy Aged Women

OBJECTIVES

To evaluate the effect of L-carnitine (LC) in combination with leucine supplementation on muscle strength and muscle hypertrophy in aged women participating in a resistance exercise training (RET) program.

DESIGN/SETTING/PARTICIPANTS

Thirty-seven out of sixty (38.3% dropout) healthy women aged 60-75 years (mean 67.6 ± 0.7 years) completed the intervention in one of three groups. One of the supplemented groups received 1 g of L-carnitine-L-tartrate in combination with 3 g of L-leucine per day (LC+L group; n = 12), and the second supplemented group received 4 g of L-leucine per day (L group; n = 13). The control group (CON group; n = 12) received no supplementation.

INTERVENTION

All three groups completed the same RET protocol involving exercise sessions twice per week for 24 weeks.

MEASUREMENTS

Before and after the experiment, participants performed isometric and isokinetic muscle strength testing on the Biodex dynamometer. The cross-sectional areas of the major knee extensors and total thigh muscles were assessed using magnetic resonance imaging. Fasting serum levels of insulin-like growth factor-1 (IGF-1), myostatin and decorin, and plasma levels of total carnitine (TC) and trimethylamine-N-oxide (TMAO) levels were measured.

RESULTS

The 24-week RET significantly increased muscle strength and muscle volume, but the group and time interactions were not significant for the muscle variables analyzed. Plasma total carnitine increased only in the LC+L group (p = 0.009). LC supplementation also caused a significant increase in plasma TMAO, which was higher after the intervention in the LC+L group than in the L (p < 0.001), and CON (p = 0.005) groups. The intervention did not change plasma TMAO concentration in the L (p = 0.959) and CON (p = 0.866) groups. After the intervention serum decorin level was higher than before in both supplemented groups combined (p = 0.012), still not significantly different to post intervention CON (p = 0.231). No changes in serum IGF-1 and myostatin concentrations and no links between the changes in blood markers and muscle function or muscle volume were observed.

CONCLUSIONS

LC combined with leucine or leucine alone does not appear to improve the effectiveness of RET.

Daily Leucine Intake Is Positively Associated with Lower Limb Skeletal Muscle Mass and Strength in the Elderly

Higher daily protein intake, with an emphasis on leucine content, is thought to mitigate age-related anabolic resistance, potentially counteracting age-related morphological and functional declines. The present study investigated potential associations between total daily leucine intake and dependent variables, including quadriceps muscle cross-sectional area (CSA) and maximum dynamic muscle strength (1-RM) in a cohort of healthy free-living older individuals of both sexes (n = 67; 34/33 men/women). Participants performed three 24 h dietary recalls and underwent a magnetic resonance imaging exam followed by 1-RM tests. Our results demonstrate moderate associations between total daily leucine and both quadriceps CSA (r = 0.42; p = 0.004) and 1-RM (r = 0.45; p = 0.001). Furthermore, our exploratory biphasic linear regression analyses, adjusted for sex, age, and protein intake relative to body weight, revealed a plateau for daily leucine intake and muscle mass and muscle strength (~7.6–8.0 g·day⁻¹) in older adults. In conclusion, we demonstrated that total daily leucine intake is associated with muscle mass and strength in healthy older individuals and this association remains after controlling for multiple factors, including overall protein intake. Furthermore, our breakpoint analysis revealed non-linearities and a potential threshold for habitual leucine intake, which may help guide future research on the effects of chronic leucine intake in age-related muscle loss.

Leucine augments specific skeletal muscle mitochondrial respiratory pathways during recovery following 7 days of physical inactivity in older adults

In older adults, leucine mitigated the loss of insulin sensitivity associated with muscular disuse. Leucine supplementation increased mitochondrial respiration and reduced a marker of oxidative stress following periods of disuse and rehabilitation.

Isolated Leucine and Branched-Chain Amino Acid Supplementation for Enhancing Muscular Strength and Hypertrophy: A Narrative Review

Branched-chain amino acids (BCAA) are one of the most popular sports supplements, marketed under the premise that they enhance muscular adaptations. Despite their prevalent consumption among athletes and the general public, the efficacy of BCAA has been an ongoing source of controversy in the sports nutrition field. Early support for BCAA supplementation was derived from extrapolation of mechanistic data on their role in muscle protein metabolism. Of the three BCAA, leucine has received the most attention because of its ability to stimulate the initial acute anabolic response. However, a substantial body of both acute and longitudinal research has now accumulated on the topic, affording the ability to scrutinize the effects of BCAA and leucine from a practical standpoint. This article aims to critically review the current literature and draw evidence-based conclusions about the putative benefits of BCAA or leucine supplementation on muscle strength and hypertrophy as well as illuminate gaps in the literature that warrant future study.

Protein Source and Muscle Health in Older Adults: A Literature Review

Research shows that higher dietary protein of up to 1.2 g/kg_bodyweight/day may help prevent sarcopenia and maintain musculoskeletal health in older individuals. Achieving higher daily dietary protein levels is challenging, particularly for older adults with declining appetites and underlying health conditions. The negative impact of these limitations on aging muscle may be circumvented through the consumption of high-quality sources of protein and/or supplementation. Currently, there is a debate regarding whether source of protein differentially affects musculoskeletal health in older adults. Whey and soy protein have been used as the most common high-quality proteins in recent literature. However, there is growing consumer demand for additional plant-sourced dietary protein options. For example, pea protein is rapidly gaining popularity among consumers, despite little to no research regarding its long-term impact on muscle health. Therefore, the objectives of this review are to: (1) review current literature from the past decade evaluating whether specific source(s) of dietary protein provide maximum benefit to muscle health in older adults; and (2) highlight the need for future research specific to underrepresented plant protein sources, such as pea protein, to then provide clearer messaging surrounding plant-sourced versus animal-sourced protein and their effects on the aging musculoskeletal system.

Prospective associations of protein intake parameters with muscle strength and physical performance in community-dwelling older men and women from the Quebec NuAge cohort

BACKGROUND

Dietary protein has been related to muscle function in aging. Beyond total intake, parameters such as protein distribution across meals might also be important.

OBJECTIVES

We aimed to examine prospective associations of different protein intake parameters with muscle strength and physical performance in community-dwelling older men and women.

METHODS

In total, 524 men and 574 women aged 67-84 y at baseline (T1) were followed annually for 3 y (T2, T3, T4). Outcomes included handgrip strength (kPa), knee extensor strength (kg), and physical performance (Timed Up and Go, s) at T4, and their 3-y changes (T4 minus T1). Protein intake parameters were assessed using nine 24-h recalls collected over 3 y (T1, T2, T3) and included daily total intake (g/d), number of protein-providing meals and snacks, and protein distribution across meals (expressed as CV). Associations were examined by multivariable linear regression models including all protein intake parameters simultaneously. Also, the optimal protein dose (g) per meal for the maximum effect size of total daily intake was determined.

RESULTS

Higher daily protein intake was associated with better knee extensor strength and physical performance at T4 in both sexes and less physical performance decline in women. Optimal protein doses per meal were 30-35 g in men and 35-50 g in women for these outcomes. In men, more uneven protein distribution was associated with better physical performance at T4 and less handgrip strength decline. In women, a higher number of protein-providing snacks was associated with better handgrip strength and knee extensor strength at T4 and less handgrip strength decline. In neither sex was number of protein-providing meals associated with outcomes.

CONCLUSIONS

Higher daily protein intake, up to 30-50 g protein/meal, may contribute to better knee extensor strength and physical performance in generally well-functioning older men and women. More aspects of protein intake may contribute to muscle strength and physical performance than solely the daily quantity, notably the protein dose per meal.

Signatures and Clinical Significance of Amino Acid Flux in Sarcopenia: A Systematic Review and Meta-Analysis

BACKGROUND

Dysregulation of amino acids is closely linked to the initiation and progression of sarcopenia. We summarized recent advancements in the studies of amino acid profiles in sarcopenia and systematically presented the clinical significance of amino acid flux in sarcopenia.

METHODS

We systematically searched in MEDLINE, EMBASE, and Cochrane library from inception to June 1, 2021 to capture all studies examining metabolomics of sarcopenia. We used the following keywords: sarcopenia, metabonomics, metabolomics, amino acid profile, and mass spectrometry. Original articles comparing amino acid patterns between persons with and without sarcopenia were included. Two independent investigators independently completed title and abstract screening, data extraction, and quality evaluation. We used a random effects model to examine the association between amino acids levels and sarcopenia. Sensitivity analyses restricted the analyses to studies in which muscle mass was measured by bioelectrical impedance analysis. Study quality was evaluated according to the Agency for Healthcare Research and Quality (AHRQ) checklist.

RESULTS

The systematic research yielded six eligible articles, comprising 1,120 participants. Five studies used muscle mass in combination with physical performance and/or muscle strength as the criteria to diagnose sarcopenia, while one study used muscle mass as a diagnostic criterion alone. We found that the concentrations of branched-chain amino acids leucine (standardized mean difference [SMD] -1.249; 95% confidence interval [CI]: -2.275, -0.223, P = 0.02, I² = 97.7%), isoleucine (SMD -1.077; 95% CI: -2.106, -0.049, P = 0.04, I² = 97.8%), and aromatic amino acid tryptophan (SMD -0.923; 95% CI: -1.580, -0.265, P = 0.01, I² = 89.9%) were significantly reduced in individuals with sarcopenia. Study results were robust in sensitivity analysis.

CONCLUSIONS

The homeostasis of amino acids is critical to maintaining muscle health. The profiles of amino acids might be useful biomarkers for the characterization of sarcopenia. Future studies are warranted to study the clinical significance of amino acids in the diagnosis and treatment of sarcopenia.

Dietary leucine requirement of older men and women is higher than current recommendations

BACKGROUND

Current national (34 mg . kg-1 . d-1) and international (39 mg kg-1 . d-1) recommendations for leucine in older adults are based on data from young adults. Evidence suggests that the leucine requirements of older adults are higher than those of young adults.

OBJECTIVE

The objective of the current study was to directly determine the leucine requirements in healthy older adult male and female study participants aged >60 y.

METHODS

Leucine requirement was determined using the indicator amino acid oxidation method (IAAO) with l-[1-13C]phenylalanine as the indicator. Sixteen older adults (n = 7 male and n = 9 female participants) were randomly assigned to receive 3 to 7 leucine intakes from 20 to 120 mg . kg-1 . d-1. The rate of release of 13CO2 from l-[1-13C]phenylalanine oxidation was measured, and breakpoint analysis was used to estimate the leucine requirement. The 95% CI was calculated using the parametric bootstrap method.

RESULTS

The mean leucine requirement for male participants was 77.8 mg . kg-1 . d-1 (upper 95% CI: 81.0) and for female participants, it was 78.2 mg . kg-1 . d-1 (upper 95% CI: 82.0) with no sex effect based on body weight. The data were therefore combined to yield a mean of 78.5 mg . kg-1 d-1 (upper 95% CI: 81.0 mg . kg-1 . d-1 ) for both sexes. On the basis of fat-free mass, the mean ± SEM leucine requirements were 115 ± 3.2 and 127 ± 2.4 mg . kg-1 . d-1 for male and female participants, respectively (P < 0.005).

CONCLUSIONS

The estimated leucine requirement of older adults is more than double the amount in current recommendations. These data suggest that leucine could be a limiting amino acid in the diet of older adults consuming the current RDA for protein and those consuming a plant-based diet. In view of the functional and structural role of leucine, especially its importance in muscle protein synthesis, current leucine recommendations of older adults should be revised. This trial was registered at clinicaltrials.gov as NCT03506126.

Protein metabolism and related body function: mechanistic approaches and health consequences

The development and maintenance of body composition and functions require an adequate protein intake with a continuous supply of amino acids (AA) to tissues. Body pool and AA cellular concentrations are tightly controlled and maintained through AA supply (dietary intake, recycled from proteolysis and de novo synthesis), AA disposal (protein synthesis and other AA-derived molecules) and AA losses (deamination and oxidation). Different molecular regulatory pathways are involved in the control of AA sufficiency including the mechanistic target of rapamycin complex 1, the general control non-derepressible 2/activating transcription factor 4 system or the fibroblast growth factor 21. There is a tight control of protein intake, and human subjects and animals appear capable of detecting and adapting food and protein intake and metabolism in face of foods or diets with different protein contents. A severely protein deficient diet induces lean body mass losses and ingestion of sufficient dietary energy and protein is a prerequisite for body protein synthesis and maintenance of muscle, bone and other lean tissues and functions. Maintaining adequate protein intake with age may help preserve muscle mass and strength but there is an ongoing debate as to the optimal protein intake in older adults. The protein synthesis response to protein intake can also be enhanced by prior completion of resistance exercise but this effect could be somewhat reduced in older compared to young individuals and gain in muscle mass and function due to exercise require regular training over an extended period.

Comprehensive overview of the quality of plant- And animal-sourced proteins based on the digestible indispensable amino acid score

Indispensable amino acid (IAA) composition and standardized ileal digestibility (SID) of five animal- and 12 plant-based proteins were used to calculate their respective Digestible Indispensable Amino Score (DIAAS) according to the three age categories defined by the Food and Agriculture Organization (FAO). Mean IAA content and mean SID obtained from each protein dataset were subsequently used to simulate optimal nutritional quality of protein mixtures. Datasets revealed considerable variation in DIAAS within the same protein source and among different protein sources. Among the selected protein sources, and based on the 0.5- to 3-year-old reference pattern, pork meat, casein, egg, and potato proteins are classified as excellent quality proteins with an average DIAAS above 100. Whey and soy proteins are classified as high-quality protein with an average DIAAS ≥75. Gelatin, rapeseed, lupin, canola, corn, hemp, fava bean, oat, pea, and rice proteins are classified in the no quality claim category (DIAAS <75). Potato, soy, and pea proteins can complement a broad range of plant proteins, leading to higher DIAAS when supplied in the form of protein mixtures and at specific ratios. Such complementarity highlights the potential to achieve an optimal nutritional efficiency with plant proteins alone.

The Impact of Protein Supplementation on Exercise-Induced Muscle Damage, Soreness and Fatigue Following Prolonged Walking Exercise in Vital Older Adults: A Randomized Double-Blind Placebo-Controlled Trial

Background: It is unknown whether protein supplementation can enhance recovery of exercise-induced muscle damage in older adults who have a disturbed muscle protein synthetic response. We assessed whether protein supplementation could attenuate exercise-induced muscle damage and soreness after prolonged moderate-intensity walking exercise in older adults. Methods: In a double-blind, placebo-controlled intervention study, 104 subjects (81% male, ≥65 years) used either a protein (n = 50) or placebo supplement (n = 54) during breakfast and directly after exercise. Within a walking event, study subjects walked 30/40/50 km per day on three consecutive days. Muscle soreness and fatigue were determined with a numeric rating scale, and creatine kinase (CK) concentrations and serum inflammation markers were obtained. Results: Habitual protein intake was comparable between the protein (0.92 ± 0.27 g/kg/d) and placebo group (0.97 ± 0.23 g/kg/d, p = 0.31). At baseline, comparable CK concentrations were found between the protein and the placebo group (110 (IQR: 84–160 U/L) and 115 (IQR: 91–186 U/L), respectively, p = 0.84). Prolonged walking (protein: 32 ± 9 km/d, placebo: 33 ± 6 km/d) resulted in a cumulative increase of CK in both the protein (∆283 (IQR: 182–662 U/L)) and placebo group (∆456 (IQR: 209–885 U/L)) after three days. CK elevations were not significantly different between groups (p = 0.43). Similarly, no differences in inflammation markers, muscle soreness and fatigue were found between groups. Conclusions: Protein supplementation does not attenuate exercise-induced muscle damage, muscle soreness or fatigue in older adults performing prolonged moderate-intensity walking exercise.

Improving Dietary Protein Quality Reduces the Negative Effects of Physical Inactivity on Body Composition and Muscle Function

BACKGROUND

Brief periods of physical inactivity can compromise muscle health. Increasing dietary protein intake is potentially beneficial but complicated by difficulties reconciling anabolic potential with a realistic food volume and energy intake. We sought to determine whether increasing dietary protein quality could reduce the negative effects of physical inactivity.

METHODS

Twenty healthy, older men and women completed 7 days of bed rest followed by 5 days of rehabilitation. Volunteers consumed a mixed macronutrient diet (MIXED: N = 10; 68 ± 2 years; 1,722 ± 29 kcal/day; 0.97 ± 0.01 g protein/kg/day) or an isoenergetic, whey-augmented, higher protein quality diet (WHEY: N = 10; 69 ± 1 years; 1,706 ± 23 kcal/day; 0.90 ± 0.01 g protein/kg/day). Outcomes included body composition, blood glucose, insulin, and a battery of physical function tests.

RESULTS

During bed rest, both groups experienced a 20% reduction in knee extension peak torque (p < .05). The WHEY diet partially protected leg lean mass (-1,035 vs. -680 ± 138 g, MIXED vs. WHEY; p = .08) and contributed to a greater loss of body fat (-90 vs. -233 ± 152 g, MIXED vs. WHEY; p < .05). Following rehabilitation, knee extension peak torque in the WHEY group fully recovered (-10.0 vs. 2.2 ± 4.1 Nm, MIXED vs. WHEY; p = .05). Blood glucose, insulin, aerobic capacity, and Short Physical Performance Battery (SPPB) changes were similar in both dietary conditions (p > .05).

CONCLUSIONS

Improving protein quality without increasing total energy intake has the potential to partially counter some of the negative effects of bed rest in older adults.

Effect of Aerobic Exercise Training and Essential Amino Acid Supplementation for 24 Weeks on Physical Function, Body Composition, and Muscle Metabolism in Healthy, Independent Older Adults: A Randomized Clinical Trial

BACKGROUND

Essential amino acids (EAA) and aerobic exercise (AE) acutely and independently stimulate skeletal muscle protein anabolism in older adults.

OBJECTIVE

In this Phase 1, double-blind, placebo-controlled, randomized clinical trial, we determined if chronic EAA supplementation, AE training, or a combination of the two interventions could improve muscle mass and function by stimulating muscle protein synthesis.

METHODS

We phone-screened 971, enrolled 109, and randomized 50 independent, low-active, nonfrail, and nondiabetic older adults (age 72 ± 1 years). We used a 2 × 2 factorial design. The interventions were: daily nutritional supplementation (15 g EAA or placebo) and physical activity (supervised AE training 3 days/week or monitored habitual activity) for 24 weeks. Muscle strength, physical function, body composition, and muscle protein synthesis were measured before and after the 24-week intervention.

RESULTS

Forty-five subjects completed the 24-week intervention. VO2peak and walking speed increased (p < .05) in both AE groups, irrespective of supplementation type, but muscle strength increased only in the EAA + AE group (p < .05). EAA supplementation acutely increased (p < .05) muscle protein synthesis from basal both before and after the intervention, with a larger increase in the EAA + AE group after the intervention. Total and regional lean body mass did not change significantly with any intervention.

CONCLUSIONS

In nonfrail, independent, healthy older adults AE training increased walking speed and aerobic fitness, and, when combined with EAA supplementation, it also increased muscle strength and EAA-stimulated muscle protein synthesis. These increases occurred without improvements in muscle mass.

Countering disuse atrophy in older adults with low-volume leucine supplementation

Older adults are at increased risk of being bedridden and experiencing negative health outcomes including the loss of muscle tissue and functional capacity. We hypothesized that supplementing daily meals with a small quantity (3-4 g/meal) of leucine would partially preserve lean leg mass and function of older adults during bed rest. During a 7-day bed rest protocol, followed by 5 days of inpatient rehabilitation, healthy older men and women (67.8 ± 1.1 yr, 14 men; 6 women) were randomized to receive isoenergetic meals supplemented with leucine (LEU, 0.06 g/kg/meal; n = 10) or an alanine control (CON, 0.06 g/kg/meal; n = 10). Outcomes were assessed at baseline, following bed rest, and after rehabilitation. Body composition was measured by dual-energy X-ray absorptiometry. Functional capacity was assessed by knee extensor isokinetic and isometric dynamometry, peak aerobic capacity, and the short physical performance battery. Muscle fiber type, cross-sectional area, signaling protein expression levels, and single fiber characteristics were determined from biopsies of the vastus lateralis. Leucine supplementation reduced the loss of leg lean mass during bed rest (LEU vs. CON: -423 vs. -1035 ± 143 g; P = 0.008) but had limited impact on strength or endurance-based functional outcomes. Similarly, leucine had no effect on markers of anabolic signaling and protein degradation during bed rest or rehabilitation. In conclusion, providing older adults with supplemental leucine has minimal impact on total energy or protein consumption and has the potential to partially counter some, but not all, of the negative effects of inactivity on muscle health.NEW & NOTEWORTHY Skeletal muscle morphology and function in older adults was significantly compromised by 7 days of disuse. Leucine supplementation partially countered the loss of lean leg mass but did not preserve muscle function or positively impact changes at the muscle fiber level associated with bed rest or rehabilitation. Of note, our data support a relationship between myonuclear content and adaptations to muscle atrophy at the whole limb and single fiber level.

Effect of branched-chain amino acid supplementation, dietary intake and circulating levels in cardiometabolic diseases: an updated review

PURPOSE OF REVIEW

Branched-chain amino acids (BCAAs) are essential amino acids derived from diet. BCAA supplementation has been recommended in elderly and athletes, but recent studies suggest an association between high dietary BCAAs and blood levels of BCAAs with greater risk of cardiometabolic diseases (CMD). This review aims to integrate current epidemiological evidence analyzing the association between BCAAs and related-CMD risk factors.

RECENT FINDINGS

Most epidemiological studies consistently show that dietary BCAAs are associated with higher risk of type-2 diabetes (T2D) whereas there is limited evidence related with other cardiovascular risk factors. Evidence also exists showing an association between higher circulating BCAA levels and risk of T2D and cardiovascular disease, and also probably with metabolic syndrome and overweight/obesity. Several clinical trials suggest beneficial cardiometabolic effect of BCAAs supplementation, although with a small sample size and short follow-up. Studies show a weak correlation between dietary BCAAs and circulating BCAA levels. Protein quality sources and whole dietary pattern are key aspects to improve our understanding of the effect of BCAAs as well as factors associated with higher protein needs, such as age or frailty.

SUMMARY

Dietary and circulating BCAAs exhibit possible detrimental cardiometabolic effects, but BCAA supplementation may have some positive influence on target groups with nutritional deficiencies.

Sarcopenia: Tilting the Balance of Protein Homeostasis

Sarcopenia, defined as age-associated decline of muscle mass and function, is a risk factor for mortality and disability, and comorbid with several chronic diseases such as type II diabetes and cardiovascular diseases. Clinical trials showed that nutritional supplements had positive effects on muscle mass, but not on muscle function and strength, demonstrating our limited understanding of the molecular events involved in the ageing muscle. Protein homeostasis, the equilibrium between protein synthesis and degradation, is proposed as the major mechanism underlying the development of sarcopenia. As the key central regulator of protein homeostasis, the mammalian target of rapamycin (mTOR) is proposed to be essential for muscle hypertrophy. Paradoxically, sustained activation of mTOR complex 1 (mTORC1) is associated with a loss of sensitivity to extracellular signaling in the elderly. It is not understood why sustained mTORC1 activity, which should induce muscle hypertrophy, instead results in muscle atrophy. Here, recent findings on the implications of disrupting protein homeostasis on muscle physiology and sarcopenia development in the context of mTOR/protein kinase B (AKT) signaling are reviewed. Understanding the role of these molecular mechanisms during the ageing process will contribute towards the development of targeted therapies that will improve protein metabolism and reduce sarcopenia.

Effect of branched-Chain Amino Acid Supplementation on Muscle Soreness following Exercise: A Meta-Analysis

Abstract. Delayed onset muscle soreness (DOMS) is a symptom of exercise-induced muscle damage that occurs following exercise. Previous research has indicated that branched-chain amino acid (BCAA) supplementation may attenuate exercise-induced muscle damage that causes delayed onset muscle soreness, however the results are inconsistent. The primary aim of this study was to examine the previous literature assessing the effect of BCAA supplementation on DOMS following an acute bout of exercise in adults. This review was conducted in accordance with PRISMA guidelines (Preferred Reporting Items for Systematic Reviews and Meta-analyses), and identified peer-reviewed articles comparing a BCAA supplement to a placebo non-BCAA supplement following an acute bout of exercise. An electronic search of three databases (EbscoHost, Web of Science, and SPORTDiscus) yielded 42 articles after duplicates were removed. All studies included in the current analyis were: 1) peer-reviewed publications; 2) available in English; 3) utilized a random control design that compared a BCAA group to a placebo control group following exercise; 4) and assessed soreness of muscle tissue during recovery. DOMS was assessed in 61 participants following ingestion of a BCAA supplement over the course of these interventions. The cumulative results of 37 effects gathered from 8 studies published between 2007 and 2017 indicated that BCAA supplementation reduced DOMS following exercise training (ES = 0.7286, 95% CI: 0.5017 to 0.9555, p < 0.001). A large decrease in DOMS occurs following BCAA supplementation after exercise compared to a placebo supplement.

Protein and amino acids for skeletal muscle health in aging

Proteins and its building blocks, amino acids, have many physiological roles in the body. While some amino acids can be synthesized endogenously, exogenous protein and amino acids are necessary to maintain homeostasis. Because skeletal muscle contains a large portion of endogenous protein and plays important roles in movement, regulation, and metabolism, imbalanced protein and amino acid availability may result in clinical conditions including skeletal muscle atrophy, impaired muscle growth or regrowth, and functional decline. Aging is associated with changes in protein metabolism and multiple physiological and functional alterations in the skeletal muscle that are accentuated by decreased dietary protein intake and impaired anabolic responses to stimuli. Inactivity and chronically elevated inflammation of the skeletal muscle can initiate and/or augment pathological remodeling of the tissue (i.e., increase of fat and fibrotic tissues and atrophy of the muscle). Defining an adequate amount of dietary protein that is appropriate to maintain the availability of amino acids for biological needs is necessary but is still widely debated for older adults. This chapter will provide (i) an overview of dietary protein and amino acids and their role in skeletal muscle health; (ii) an overview of skeletal muscle structure and function and the deterioration of muscle that occurs with advancing age; (iii) a discussion of the relationship between protein/amino acid metabolism and skeletal muscle decline with aging; and (iv) a brief discussion of optimal protein intakes for older adults to maintain skeletal muscle health in aging.

Daily Protein Intake and Distribution of Daily Protein Consumed Decreases Odds for Functional Disability in Older Americans

Objective: We sought to determine whether daily protein intake and protein distribution across eating occasions were associated with functional disability in a national sample of older Americans. Methods: Data from 8,070 adults aged ≥60 years from the 2007-2016 waves of the National Health and Nutrition Examination Survey were included. Protein intake and functional capacity was self-reported. A daily protein recommendation of ≥1.0 g/kg/day was utilized. The daily protein recommendation was then spread-out across four meals, whereby a ≥0.25 g/kg/meal threshold was used. Results: Those meeting the daily protein recommendation had 0.78 (95% confidence interval [CI] = [0.65, 0.93]) decreased odds for functional disability. Persons meeting the protein intake threshold per eating occasion for one, two, three, and four occasions had 0.60 (CI = [0.38, 0.95]), 0.48 (CI = [0.30, 0.77]), 0.47 (CI = [0.29, 0.77]), and 0.39 (CI = [0.20, 0.75]) decreased odds for functional disability, respectively. Discussion: Protein consumption seems to be important for preserving function in older Americans.

Beneficial Effects of Leucine Supplementation on Criteria for Sarcopenia: A Systematic Review

Objective: Treating sarcopenia remains a challenge, and nutritional interventions present promising approaches. We summarize the effects of leucine supplementation in treating older individuals with sarcopenia associated with aging or to specific disorders, and we focus on the effect of leucine supplementation on various sarcopenia criteria, e.g., muscular strength, lean mass, and physical performance. Methods: A literature search for articles related to this topic was performed on the relevant databases, e.g., the PubMed/Medline, Embase, EBSCO, Cochrane, Lilacs, and Dialnet. The identified articles were reviewed according to Preferred Reporting Items for Systematic reviews and meta-analyses (PRISMA) guidelines. Results: Of the 163 articles we consulted, 23 met our inclusion criteria, analysing the effect of leucine or leucine-enriched protein in the treatment of sarcopenia, and 13 of these studies were based on randomized and placebo-controlled trials (RCTs). In overall terms, the published results show that administration of leucine or leucine-enriched proteins (range 1.2–6 g leucine/day) is well-tolerated and significantly improves sarcopenia in elderly individuals, mainly by improving lean muscle-mass content and in this case most protocols also include vitamin D co-administration. The effect of muscular strength showed mix results, and the effect on physical performance has seldom been studied. For sarcopenia-associated with specific disorders, the most promising effects of leucine supplementation are reported for the rehabilitation of post-stroke patients and in those with liver cirrhosis. Further placebo-controlled trials will be necessary to determine the effects of leucine and to evaluate sarcopenia with the criteria recommended by official Working Groups, thereby limiting the variability of methodological issues for sarcopenia measurement across studies.

A review of the alleged health hazards of monosodium glutamate

Monosodium glutamate (MSG) is an umami substance widely used as flavor enhancer. Although it is generally recognized as being safe by food safety regulatory agencies, several studies have questioned its long-term safety. The purpose of this review was to survey the available literature on preclinical studies and clinical trials regarding the alleged adverse effects of MSG. Here, we aim to provide a comprehensive overview of the reported possible risks that may potentially arise following chronic exposure. Furthermore, we intend to critically evaluate the relevance of this data for dietary human intake. Preclinical studies have associated MSG administration with cardiotoxicity, hepatotoxicity, neurotoxicity, low-grade inflammation, metabolic disarray and premalignant alterations, along with behavioral changes. Moreover, links between MSG consumption and tumorigenesis, increased oxidative stress and apoptosis in thymocytes, as well as genotoxic effects in lymphocytes have been reported. However, in reviewing the available literature, we detected several methodological flaws, which led us to conclude that these studies have limited relevance for extrapolation to dietary human intakes of MSG risk exposure. Clinical trials have focused mainly on the effects of MSG on food intake and energy expenditure. Besides its well-known impact on food palatability, MSG enhances salivary secretion and interferes with carbohydrate metabolism, while the impact on satiety and post-meal recovery of hunger varied in relation to meal composition. Reports on MSG hypersensitivity, also known as 'Chinese restaurant syndrome', or links of its use to increased pain sensitivity and atopic dermatitis were found to have little supporting evidence. Based on the available literature, we conclude that further clinical and epidemiological studies are needed, with an appropriate design, accounting for both added and naturally occurring dietary MSG. Critical analysis of existing literature, establishes that many of the reported negative health effects of MSG have little relevance for chronic human exposure and are poorly informative as they are based on excessive dosing that does not meet with levels normally consumed in food products.

Leucine Supplementation Does Not Alter Insulin Sensitivity in Prefrail and Frail Older Women following a Resistance Training Protocol

BACKGROUND

Frailty is a clinical condition associated with loss of muscle mass and strength (sarcopenia). Although sarcopenia has multifactorial causes, it might be partly attributed to a blunted response to anabolic stimuli. Leucine acutely increases muscle protein synthesis, and resistance training (RT) is the strongest stimuli to counteract sarcopenia and was recently shown to improve insulin sensitivity (IS) in frail older women. Discrepancies exist regarding whether chronic supplementation of leucine in conjunction with RT can improve muscle mass and IS.

OBJECTIVE

The aim of this double-blinded placebo-controlled study was to determine the effects of leucine supplementation and RT on IS in prefrail and frail older women.

METHODS

Using the Fried criteria, 19 nondiabetic prefrail (1-2 criteria) and frail (≥3 criteria) older women (77.5 ± 1.3 y; body mass index (kg/m2): 25.1 ± 0.9) underwent a 3-mo intervention of RT 3 times/wk with protein-optimized diet of 1.2 g·kg-1·d-1 and 7.5 g·d-1 of l-leucine supplementation compared with placebo l-alanine. Pre-/postintervention primary outcomes were fasting plasma glucose, serum insulin, and 4-h responses to a standard meal of complete liquid formula. Secondary outcomes of resting energy expenditure using indirect calorimetry and body composition using dual-energy X-ray absorptiometry were obtained. Paired t tests analyzed pooled data, and 2-factor repeated-measures ANOVA determined supplementation, training, and interaction effects.

RESULTS

No significant time, group, or interaction effects were observed for postprandial areas under the curve of serum insulin or plasma glucose or for resting energy expenditure in l-leucine compared with l-alanine. Total lean body mass increased and percentage body fat decreased significantly for both groups postintervention (0.76 ± 0.13 and -0.92 ± 0.33 kg, respectively; time effect: P < 0.01).

CONCLUSIONS

IS was not affected by RT and leucine supplementation in nondiabetic prefrail and frail older women. Therefore, leucine supplementation does not appear to influence IS under these conditions. This trial was registered at clinicaltrials.gov as NCT01922167.

Dietary branched-chain amino acids intake exhibited a different relationship with type 2 diabetes and obesity risk: a meta-analysis

AIM

To assess whether oral branched-chain amino acids (BCAA) supplementation exerts influence on circulating BCAA and the significance of dietary BCAA in type 2 diabetes and obesity risk.

METHOD

We searched PUBMED, EMBASE and Cochrane library through June 2018 to retrieve and screen published reports for inclusion in the meta-analysis after methodological assessment. Heterogeneity of studies was evaluated using I² statistics, while sensitivity analysis and funnel plot were used to evaluate the potential effect of individual studies on the overall estimates and publication bias, respectively, using RevMan 5.3.

RESULT

Eight articles on randomized clinical trial of oral BCAA supplementation, and seven articles on dietary BCAA intake and type 2 diabetes/obesity risks were eligible for inclusion in our meta-analyses. Mean difference and 95% confidence interval (CI) of circulating leucine was 39.65 (3.54, 75.76) µmol/L, P = 0.03 post-BCAA supplementation. Also, OR and 95% CI for higher total BCAA intake and metabolic disorder risks were, 1.32 (1.14, 1.53), P = 0.0003-type 2 diabetes and 0.62 (0.47, 0.82), P = 0.0008-obesity.

CONCLUSION

Oral BCAA supplementation exerts modest influence on circulating leucine profile and higher total BCAA intake is positively and contra-positively associated with type 2 diabetes and obesity risk, respectively.

Nutritional Interventions for Elderly and Considerations for the Development of Geriatric Foods

The process of aging is characterized by numerous changes in the body which has an overall negative effect on the health and lifestyle of elderly. Nutrition deserves special attention as an individual reaches old age. It plays a vital role in affecting the quality of life, including physical, mental and social health. The physiological decline in food intake is very common among older age and this result in nutritional deficiencies. These increased nutritional deficiencies are the major risk factors for certain chronic diseases and deteriorated age related health. Thus, the adoption of nutritional intervention can be a measure to tackle the current situation of nutritional deficiencies and promote a healthy lifestyle.

Protein Intake Recommendation for Korean Older Adults to Prevent Sarcopenia: Expert Consensus by the Korean Geriatric Society and the Korean Nutrition Society

Sarcopenia, a common clinical syndrome in older adults, is defined as decreased muscle mass, strength, and physical performance. Since sarcopenia is associated with the incidence of functional decline, falls, and even mortality in older adults, researchers and health care providers have been keen to accumulate clinical evidence to advocate the screening and prevention of sarcopenia progression in older adults. The factors that may accelerate the loss of muscle mass and function include chronic diseases, inactivity, and deficiency in appropriate nutritional support. Among these, nutritional support is considered an initial step to delay the progression of muscle wasting and improve physical performance in community-dwelling older adults. However, a nationwide study suggested that most Korean older adults do not consume sufficient dietary protein to maintain their muscle mass. Furthermore, considering age-associated anabolic resistance to dietary protein, higher protein intake should be emphasized in older adults than in younger people. To develop a dietary protein recommendation for older adults in Korea, we reviewed the relevant literature, including interventional studies from Korea. From these, we recommend that older adults consume at least 1.2 g of protein per kg of body weight per day (g/kg/day) to delay the progression of muscle wasting. The amount we recommend (1.2 g/kg/day) is 31.4% higher than the previously suggested recommended daily allowance (i.e., 0.91 g/kg/day) for the general population of Korea. Also, evidence to date suggests that the combination of exercise and nutritional support may enhance the beneficial effects of protein intake in older adults in Korea. We found that the current studies are insufficient to build population-based guidelines for older adults, and we call for further researches in Korea.

Higher intakes of energy-adjusted dietary amino acids are inversely associated with obesity risk

We assessed the relationship between energy-adjusted amino acids (EAA) intakes and obesity risk using data on nutrient intakes derived from the Chinese food composition tables to determine dietary intakes (DI) among 1109 obese and 3009 normal weight subjects. Dietary patterns (DP) were identified using principal component analysis, multivariable-adjusted odds ratio (OR) and 95% confidence interval (CI) of obesity risk by quartiles of EAA intakes was estimated using logistic regression with two-sided P < 0.05. Multivariable-adjusted OR and 95% CI for obesity risk were 1.00, 0.801 (0.573, 1.119), 0.718 (0.504, 1.024) and 0.532 (0.353, 0.803) P-trend = 0.003 across energy-adjusted quartiles of total AA intakes. Similarly, higher DI of 13 AA; isoleucine, leucine, valine, lysine, cysteine, phenylalanine, tyrosine, threonine, histidine, aspartic acid, glutamic acid, proline, and serine were associated with lower risk of obesity. Furthermore, six DP; 'Wheaten food and Rice', 'Fruit, Vegetables and Milk', 'Snack, Beverage and Ice cream', 'Potatoes, Soybean & Egg', 'Livestock & Poultry meat' and 'Fish' were identified. Multivariable-adjusted OR and 95% CI across quartiles of DP adherence for obesity risk were 1.00, 0.737 (0.535, 1.017), 0.563 (0.406, 0.779), 0.724 (0.518, 1.011) P-trend = 0.018 for 'Fruit, Vegetables and Milk', 1.00, 0.734 (0.531, 1.013), 0.841(0.609, 1.161), 0.657 (0.478, 0.904) P-trend = 0.027 for 'Potatoes, Soybean & Egg' and 1.00, 1.106 (0.791, 1.548), 1.367(0.975, 1.917), 1.953 (1.399, 2.726) P-trend = 0.000 for 'Fish'. Additionally, lower adherence to 'Snack, Beverage and Ice cream' and 'Fish' patterns is associated with a protective higher AA intake-obesity risk relationship. Energy-adjusted AA intakes were inversely associated with obesity risk, but the associations appear modifiable by DP adherence of respondents.

[Low protein diet supplemented with ketoanalogues of amino acids in patients with chronic renal insufficiency]

Restricted protein diets in patients with chronic kidney disease have been debated for several decades. In chronic kidney disease as in other chronic diseases, the modulation of the nutritional intake is the object of a certain renewal. It is supported by recent studies that highlight the importance of modulating nutrient intake by diets that are healthier, less rich in animal proteins and richer in plants. The recent reintroduction in France of amino acid supplements and ketoanalogs of amino acids allows the prescription of a very restricted diet. Historical studies have only focused on the relationship between protein intake and renal function degradation. Recent studies on acid loading, bone metabolism or potassium intake allow revisiting the interest of restricted diets. As with any change in eating habits, the selection of patients, information, education and monitoring during the diet are very important and help prevent undernutrition: this is the purpose of this short review.

Determinants of muscle preservation in individuals with cerebral palsy across the lifespan: a narrative review of the literature

In individuals with cerebral palsy (CP), smaller muscle and atrophy are present at young age. Many people with CP also experience a decline in gross motor function as they age, which might be explained by the loss of muscle mass. The clinical observation of muscle wasting has prompted a comparison with sarcopenia in older adults, and the term accelerated musculoskeletal ageing is often used to describe the hallmark phenotype of CP through the lifespan. However, there has been very little research emphasis on the natural history of ageing with CP and even less with respect to the determinants or prevention of muscle loss with CP. Considering the burgeoning interest in the science of muscle preservation, this paper aims to (i) describe the characteristics of accelerated musculoskeletal ageing in people with CP, (ii) describe the pathophysiology of sarcopenia and parallels with CP, and (iii) discuss possible therapeutic approaches, based on established approaches for sarcopenia.

Leucine Supplementation Does Not Attenuate Skeletal Muscle Loss during Leg Immobilization in Healthy, Young Men

BACKGROUND

Short successive periods of physical inactivity occur throughout life and contribute considerably to the age-related loss of skeletal muscle mass. The maintenance of muscle mass during brief periods of disuse is required to prevent functional decline and maintain metabolic health.

OBJECTIVE

To assess whether daily leucine supplementation during a short period of disuse can attenuate subsequent muscle loss in vivo in humans.

METHODS

Thirty healthy (22 ± 1 y) young males were exposed to a 7-day unilateral knee immobilization intervention by means of a full leg cast with (LEU, n = 15) or without (CON, n = 15) daily leucine supplementation (2.5 g leucine, three times daily). Prior to and directly after immobilization, quadriceps muscle cross-sectional area (computed tomography (CT) scan) and leg strength (one-repetition maximum (1-RM)) were assessed. Furthermore, muscle biopsies were taken in both groups before and after immobilization to assess changes in type I and type II muscle fiber CSA.

RESULTS

Quadriceps muscle cross-sectional area (CSA) declined in the CON and LEU groups (p < 0.01), with no differences between the two groups (from 7712 ± 324 to 7287 ± 305 mm² and from 7643 ± 317 to 7164 ± 328 mm²; p = 0.61, respectively). Leg muscle strength decreased from 56 ± 4 to 53 ± 4 kg in the CON group and from 63 ± 3 to 55 ± 2 kg in the LEU group (main effect of time p < 0.01), with no differences between the groups (p = 0.052). Type I and II muscle fiber size did not change significantly over time, in both groups (p > 0.05).

CONCLUSIONS

Free leucine supplementation with each of the three main meals (7.5 g/d) does not attenuate the decline of muscle mass and strength during a 7-day limb immobilization intervention.

Metabolic fingerprinting of joint tissue of collagen-induced arthritis (CIA) rat: In vitro, high resolution NMR (nuclear magnetic resonance) spectroscopy based analysis

Rheumatoid arthritis (RA) is a systemic autoimmune disease whose major characteristics persistent joint inflammation that results in joint destruction and failure of the function. Collagen-induced arthritis (CIA) rat is an autoimmune disease model and in many ways shares features with RA. The CIA is associated with systemic manifestations, including alterations in the metabolism. Nuclear magnetic resonance (NMR) spectroscopy-based metabolomics has been successfully applied to the perchloric acid extract of the joint tissue of CIA rat and control rat for the analysis of aqueous metabolites. GPC (Glycerophosphocholine), carnitine, acetate, and creatinine were important discriminators of CIA rats as compared to control rats. Level of lactate (significance; p = 0.004), alanine (p = 0.025), BCA (Branched-chain amino acids) (p = 0.006) and creatinine (p = 0.023) was significantly higher in CIA rats as compared to control rats. Choline (p = 0.038) and GPC (p = 0.009) were significantly reduced in CIA rats as compared to control rats. Choline to GPC correlation was good and negative (Pearson correlation = -0.63) for CIA rats as well as for control rats (Pearson correlation = -0.79). All these analyses collectively considered as metabolic fingerprinting of the joint tissue of CIA rat as compared to control rat. The metabolic fingerprinting of joint tissue of CIA rats was different as compared to control rats. The metabolic fingerprinting reflects inflammatory disease activity in CIA rats with synovitis, demonstrating that underlying inflammatory process drives significant changes in metabolism that can be measured in the joint tissue. Therefore, the outcome of this study may be helpful for understanding the mechanism of metabolic processes in RA. This may be also helpful for the development of advanced diagnostic methods and therapy for RA.

Strength training increases skeletal muscle quality but not muscle mass in old institutionalized adults: a randomized, multi-arm parallel and controlled intervention study

BACKGROUND

Age related loss of skeletal muscle mass is accompanied by changes in muscle quality leading to impairment of functional status.

AIM

This study investigated the effect of resistance training and nutritional supply on muscle mass and muscle quality in very old institutionalized adults.

DESIGN

Prospective, randomized, multi-arm parallel and controlled intervention study.

SETTING

This study was conducted in five retirement care facilities.

POPULATION

This subgroup of the Vienna Active Ageing Study included 54 women and men (82.4±6.0 years) with impaired health status. Participants were randomly assigned either to elastic band resistance training (N.=16), training with nutritional supplementation (N.=21) or control group (N.=17).

METHODS

Health status was assessed at baseline with functional tests, cognitive status, nutritional status, sum of medications as well as sum of diseases. Skeletal muscle mass, determined by dual-energy X-ray absorptiometry, isokinetic knee extension and flexion force and handgrip strength were assessed at baseline and after 6 months. Muscle quality of lower extremities was defined as ratio of the extensor (MQ_LE (Ext.)) or flexor strength (MQ_LE (Flex.)) to lean leg mass. Muscle quality of upper extremity was defined as ratio of handgrip strength to lean arm mass. Follow-up examinations were performed after 12 and 18 months of intervention.

RESULTS

Muscle quality, but not muscle mass, showed significant correlations to functional tests at baseline (0.300 - 0.614, P<0.05). Resistance training significantly enhanced muscle quality of lower extremity after 6 months (MQ_LE (Ext.) +19.8%, MQ_LE (Flex.) +30.8%, P<0.05). Nutritional supplementation could not further increase the training effect. Participants with lower muscle quality at baseline benefit most from the training intervention. Skeletal muscle mass was not changed by any intervention.

CONCLUSIONS

Resistance training with elastic bands improved muscle quality in very old people. Additional nutritional supplementation was not able to further improve the effects obtained by training alone.

CLINICAL REHABILITATION IMPACT

Elastic band resistance training could be safely used to improve muscle quality even in old people with impaired health status. Weak and chronically ill participants benefit most from this training.

Obesity Interventions for Older Adults: Diet as a Determinant of Physical Function

Throughout the world, a high prevalence of obesity in older populations has created a new phenotype of frailty: the obese, functionally frail older adult. The convergence of the obesity epidemic with global graying will undoubtedly increase the prevalence of this concern. Barriers to treatment include ambiguities about the appropriate level of obesity that should trigger an intervention, due to age-related physiologic changes and a lack of consensus on specific criteria and cutoffs. Moreover, obesity interventions for this population have been limited by concerns about negative effects on lean mass, bone mineral density, and even mortality. However, newly reported approaches for restoring physical function by obesity reduction have shown good short-term efficacy. Because the majority of these interventions have used exercise as part of the treatment, this review focuses specifically on current understanding of the discrete effects of dietary interventions for geriatric obesity with regards to functional outcomes on tests including the Short Physical Performance Battery, the Physical Performance Test, and the Western Ontario and McMaster Universities Osteoarthritis Index. The literature showed roughly equal benefits to function from a weight reduction diet or exercise regimen, although neither modality was as efficacious alone as the 2 combined. Only 1 of 3 studies of protein intake during weight loss showed a positive effect of protein on function, but findings to date are too limited to prove or disprove a protein benefit. We conclude that although diet and exercise should be combined whenever possible, it remains important to further investigate the beneficial and likely unique effects that calorie restriction and/or nutrient modification can provide, particularly for obese and functionally frail older populations.

BCAA Metabolism and Insulin Sensitivity - Dysregulated by Metabolic Status?

Branched-chain amino acids (BCAAs) appear to influence several synthetic and catabolic cellular signaling cascades leading to altered phenotypes in mammals. BCAAs are most notably known to increase protein synthesis through modulating protein translation, explaining their appeal to resistance and endurance athletes for muscle hypertrophy, expedited recovery, and preservation of lean body mass. In addition to anabolic effects, BCAAs may increase mitochondrial content in skeletal muscle and adipocytes, possibly enhancing oxidative capacity. However, elevated circulating BCAA levels have been correlated with severity of insulin resistance. It is hypothesized that elevated circulating BCAAs observed in insulin resistance may result from dysregulated BCAA degradation. This review summarizes original reports that investigated the ability of BCAAs to alter glucose uptake in consequential cell types and experimental models. The review also discusses the interplay of BCAAs with other metabolic factors, and the role of excess lipid (and possibly energy excess) in the dysregulation of BCAA catabolism. Lastly, this article provides a working hypothesis of the mechanism(s) by which lipids may contribute to altered BCAA catabolism, which often accompanies metabolic disease.