Muscle full effect after oral protein: time-dependent concordance and discordance between human muscle protein synthesis and mTORC1 signaling

Green Tea Extract Concurrent with an Oral Nutritional Supplement Acutely Enhances Muscle Microvascular Blood Flow without Altering Leg Glucose Uptake in Healthy Older Adults

Postprandial macro- and microvascular blood flow and metabolic dysfunction manifest with advancing age, so vascular transmuting interventions are desirable. In this randomised, single-blind, placebo-controlled, crossover trial, we investigated the impact of the acute administration of green tea extract (GTE; containing ~500 mg epigallocatechin-3-gallate) versus placebo (CON), alongside an oral nutritional supplement (ONS), on muscle macro- and microvascular, cerebral macrovascular (via ultrasound) and leg glucose/insulin metabolic responses (via arterialised/venous blood samples) in twelve healthy older adults (42% male, 74 ± 1 y). GTE increased m. vastus lateralis microvascular blood volume (MBV) at 180 and 240 min after ONS (baseline: 1.0 vs. 180 min: 1.11 ± 0.02 vs. 240 min: 1.08 ± 0.04, both p < 0.005), with MBV significantly higher than CON at 180 min (p < 0.05). Neither the ONS nor the GTE impacted m. tibialis anterior perfusion (p > 0.05). Leg blood flow and vascular conductance increased, and vascular resistance decreased similarly in both conditions (p < 0.05). Small non-significant increases in brachial artery flow-mediated dilation were observed in the GTE only and middle cerebral artery blood flow did not change in response to GTE or CON (p > 0.05). Glucose uptake increased with the GTE only (0 min: 0.03 ± 0.01 vs. 35 min: 0.11 ± 0.02 mmol/min/leg, p = 0.007); however, glucose area under the curve and insulin kinetics were similar between conditions (p > 0.05). Acute GTE supplementation enhances MBV beyond the effects of an oral mixed meal, but this improved perfusion does not translate to increased leg muscle glucose uptake in healthy older adults.

Sarcopenia and blood albumin: A systematic review with meta-analysis

Sarcopenia is characterized by loss of muscle mass during aging, which can have consequences for the individuals’ health. There are many ways to detect it, among them, with the use of blood biomarkers such as albumin, although the association between the two has not been confirmed yet. This review synthesizes the knowledge on the association between sarcopenia and serum albumin among elderly individuals through a systematic review and meta-analysis focused on the etiology and risk factors. We used the Joanna Briggs Institute software for the review and conducted a search in MEDLINE, Embase, CINAHL, and LILACS databases while two reviewers conducted an independent manual search. EpiDat, version 3.1 was used for the meta-analysis; mean differences with the albumin scores disaggregated by sarcopenia were analyzed by the random-effects model. The degree of heterogeneity was assessed with the DerSimonian and Laird Q test. We analyzed 630 articles and finally included 14 in the review. Higher blood albumin levels were found in the meta-analysis, which was statistically significant among the elderly adults who did not present sarcopenia compared to those who did. Although there are studies exploring the association between albumin and sarcopenia, there is a need to continue evaluating its association with biological markers and comparing them to verify which can be used to detect sarcopenia among the elderly.

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

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

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Anabolic effects of oral leucine-rich protein with and without β-hydroxybutyrate on muscle protein metabolism in a novel clinical model of systemic inflammation-a randomized crossover trial

BACKGROUND

β-lactoglobulin (BLG) stimulates muscle protein synthesis and β-hydroxybutyrate (BHB) inhibits muscle breakdown. Whether combining the 2 can additively attenuate disease-induced muscle loss is unknown.

OBJECTIVE

Based on previous observations of anticatabolic effects of protein and ketone bodies during inflammation, and using a novel model combining ongoing systemic inflammation, fasting, and immobilization, we tested whether the anticatabolic muscle response to oral amino acids is altered compared with control conditions, as well as whether coadministration of oral BHB and BLG further improves the muscle anabolic response. Muscle net balance (NBphe) was the primary outcome and intramyocellular signals were assessed.

METHODS

In a randomized crossover design, 8 young men underwent either preconditioning with LPS (prestudy day: 1 ng/kg, study day: 0.5 ng/kg) combined with a 36-h fast and bed rest to mimic catabolic inflammatory disease (CAT) or an overnight fast (control [CTR]) prior to isocaloric nutritional interventions on 3 occasions separated by ∼6 wk (range 42 to 83 d).

RESULTS

NBphe increased similarly upon all conditions (interaction P = 0.65). From comparable baseline rates, both Rdphe [muscle synthesis, median ratio (95% CI): 0.44 (0.23, 0.86) P = 0.017] and Raphe [muscle breakdown, median ratio (95% CI): 0.46 (0.27, 0.78) P = 0.005] decreased following BHB + BLG compared with BLG. BLG increased Rdphe more under CAT conditions compared with CTR (interaction P = 0.02). CAT increased inflammation, energy expenditure, and lipid oxidation and decreased Rdphe and anabolic signaling [mammalian target of rapamycin (mTOR) and eukaryotic translation initiation factor 4E-binding protein 1 (4EPB1) phosphorylation].

CONCLUSION

In contrast to our initial hypothesis, NBphe increased similarly following BLG during CAT and CTR conditions; CAT however, specifically stimulated the BLG-mediated increase in protein synthesis, whereas BHB coadministration did not affect NBphe, but distinctly dampened the BLG-induced increase in muscle amino acid fluxes thereby liberating circulating amino acids for anabolic actions elsewhere.

Feeding female soldiers: Consideration of sex-specific nutrition recommendations to optimise the health and performance of military personnel

Appropriate nutrition recommendations are required to optimise the health and performance of military personnel, yet limited data are available on whether male and female military personnel have different nutrition requirements.

OBJECTIVES

To consider the evidence for sex-specific nutrition requirements to optimise the health and performance of military personnel.

DESIGN

Narrative review.

METHODS

Published literature was reviewed, with a focus on sex-specific requirements, in the following areas: nutrition for optimising muscle mass and function, nutrition during energy deficit, and nutrition for reproductive and bone health.

RESULTS

There are limited data on sex differences in protein requirements but extant data suggest that, despite less muscle mass, on average, in women, sex-specific protein feeding strategies are not required to optimise muscle mass in military-aged individuals. Similarly, despite sex differences in metabolic and endocrine responses to energy deficit, current data do not suggest a requirement for sex-specific feeding strategies during energy deficit. Energy deficit impairs health and performance, most notably bone and reproductive health and these impairments are greater for women. Vitamin D, iron and calcium are important nutrients to protect the bone health of female military personnel due to increased risk of stress fracture.

CONCLUSIONS

Women have an increased incidence of bone injuries, less muscle mass and are more susceptible to the negative effects of energy deficit, including compromised reproductive health. However, there are limited data on sex differences in response to various nutrition strategies designed to improve these elements of health and performance. Future studies should evaluate whether sex-specific feeding recommendations are required.

Evaluating the Leucine Trigger Hypothesis to Explain the Post-prandial Regulation of Muscle Protein Synthesis in Young and Older Adults: A Systematic Review

Background: The "leucine trigger" hypothesis was originally conceived to explain the post-prandial regulation of muscle protein synthesis (MPS). This hypothesis implicates the magnitude (amplitude and rate) of post-prandial increase in blood leucine concentrations for regulation of the magnitude of MPS response to an ingested protein source. Recent evidence from experimental studies has challenged this theory, with reports of a disconnect between blood leucine concentration profiles and post-prandial rates of MPS in response to protein ingestion. Aim: The primary aim of this systematic review was to qualitatively evaluate the leucine trigger hypothesis to explain the post-prandial regulation of MPS in response to ingested protein at rest and post-exercise in young and older adults. We hypothesized that experimental support for the leucine trigger hypothesis will depend on age, exercise status (rest vs. post-exercise), and type of ingested protein (i.e., isolated proteins vs. protein-rich whole food sources). Methods: This qualitative systematic review extracted data from studies that combined measurements of post-prandial blood leucine concentrations and rates of MPS following ingested protein at rest and following exercise in young and older adults. Data relating to blood leucine concentration profiles and post-prandial MPS rates were extracted from all studies, and reported as providing sufficient or insufficient evidence for the leucine trigger hypothesis. Results: Overall, 16 of the 29 eligible studies provided sufficient evidence to support the leucine trigger hypothesis for explaining divergent post-prandial rates of MPS in response to different ingested protein sources. Of these 16 studies, 13 were conducted in older adults (eight of which conducted measurements post-exercise) and 14 studies included the administration of isolated proteins. Conclusion: This systematic review underscores the merits of the leucine trigger hypothesis for the explanation of the regulation of MPS. However, our data indicate that the leucine trigger hypothesis confers most application in regulating the post-prandial response of MPS to ingested proteins in older adults. Consistent with our hypothesis, we provide data to support the idea that the leucine trigger hypothesis is more relevant within the context of ingesting isolated protein sources rather than protein-rich whole foods. Future mechanistic studies are warranted to understand the complex series of modulatory factors beyond blood leucine concentration profiles within a food matrix that regulate post-prandial rates of MPS.

Should nutritional therapy be modified to account for mitochondrial dysfunction in critical illness?

Metabolic dysfunction, and its associated muscle atrophy, remains the most common complication of critical care. At the centre of this is mitochondrial dysfunction, secondary to hypoxia and systemic inflammation. This leads to a bioenergetic crisis, with decreased intramuscular adenosine tri-phosphate content and a reduction in the highly energy dependent process of protein synthesis. Numerous methods have been studied to try and reduce these effects, with only limited success. Trials investigating the use of increased calorie and protein administration have instead found a decrease in relative lean body mass, and a potential increase in morbidity and mortality. Ketone bodies have been proposed as alternative substrates for metabolism in critical illness, with promising results seen in animal models. They are currently being investigated in critical care patients in the Alternative Substrates in the Critically Ill Subjects trial. The evidence to date suggests that individualised feeding regimens may be key in the nutritional approach to critical illness. Consideration of individual patient factors will need to be combined with personalised protein content, total energy load received, and the timings of such feeds. This review covers mitochondrial dysfunction in critical illness, and how it contributes to muscle wasting and the resultant morbidity and mortality and the scientific basis of why current nutritional approaches to date have not been successful in negating this effect. These two factors underpin the need for consideration of alternative nutritional strategies in the critically ill patient. This article is protected by copyright. All rights reserved.

A Muscle-Centric Perspective on Intermittent Fasting: A Suboptimal Dietary Strategy for Supporting Muscle Protein Remodeling and Muscle Mass?

Muscle protein is constantly “turning over” through the breakdown of old/damaged proteins and the resynthesis of new functional proteins, the algebraic difference determining net muscle gain, maintenance, or loss. This turnover, which is sensitive to the nutritional environment, ultimately determines the mass, quality, and health of skeletal muscle over time. Intermittent fasting has become a topic of interest in the health community as an avenue to improve health and body composition primarily via caloric deficiency as well as enhanced lipolysis and fat oxidation secondary to attenuated daily insulin response. However, this approach belies the established anti-catabolic effect of insulin on skeletal muscle. More importantly, muscle protein synthesis, which is the primary regulated turnover variable in healthy humans, is stimulated by the consumption of dietary amino acids, a process that is saturated at a moderate protein intake. While limited research has explored the effect of intermittent fasting on muscle-related outcomes, we propose that infrequent meal feeding and periods of prolonged fasting characteristic of models of intermittent fasting may be counter-productive to optimizing muscle protein turnover and net muscle protein balance. The present commentary will discuss the regulation of muscle protein turnover across fasted and fed cycles and contrast it with studies exploring how dietary manipulation alters the partitioning of fat and lean body mass. It is our position that intermittent fasting likely represents a suboptimal dietary approach to remodel skeletal muscle, which could impact the ability to maintain or enhance muscle mass and quality, especially during periods of reduced energy availability.

The role of protein hydrolysates for exercise-induced skeletal muscle recovery and adaptation: a current perspective

The protein supplement industry is expanding rapidly and estimated to have a multi-billion market worth. Recent research has centred on understanding how the manufacturing processes of protein supplements may impact muscle recovery and remodeling. The hydrolysed forms of protein undergo a further heating extraction process during production which may contribute to amino acids (AA) appearing in circulation at a slightly quicker rate, or greater amplitude, than the intact form. Whilst the relative significance of the rate of aminoacidemia to muscle protein synthesis is debated, it has been suggested that protein hydrolysates, potentially through the more rapid delivery and higher proportion of di-, tri- and smaller oligo-peptides into circulation, are superior to intact non-hydrolysed proteins and free AAs in promoting skeletal muscle protein remodeling and recovery. However, despite these claims, there is currently insufficient evidence to support superior muscle anabolic properties compared with intact non-hydrolysed proteins and/or free AA controls. Further research is warranted with appropriate protein controls, particularly in populations consuming insufficient amounts of protein, to support and/or refute an important muscle anabolic role of protein hydrolysates. The primary purpose of this review is to provide the reader with a current perspective on the potential anabolic effects of protein hydrolysates in individuals wishing to optimise recovery from, and maximise adaptation to, exercise training.

Principles of stable isotope research - with special reference to protein metabolism

The key to understanding the mechanisms regulating disease stems from the ability to accurately quantify the dynamic nature of the metabolism underlying the physiological and pathological changes occurring as a result of the disease. Stable isotope tracer technologies have been at the forefront of this for almost 80 years now, and through a combination of both intense theoretical and technological development over these decades, it is now possible to utilise stable isotope tracers to investigate the complexities of in vivo human metabolism from a whole body perspective, down to the regulation of sub-nanometer cellular components (i.e organelles, nucleotides and individual proteins). This review therefore aims to highlight; 1) the advances made in these stable isotope tracer approaches - with special reference given to their role in understanding the nutritional regulation of protein metabolism, 2) some considerations required for the appropriate application of these stable isotope techniques to study protein metabolism, 3) and finally how new stable isotopes approaches and instrument/technical developments will help to deliver greater clinical insight in the near future.

Ammonium chloride administration prior to exercise has muscle-specific effects on mitochondrial and myofibrillar protein synthesis in rats

AIM

Exercise is able to increase both muscle protein synthesis and mitochondrial biogenesis. However, acidosis, which can occur in pathological states as well as during high-intensity exercise, can decrease mitochondrial function, whilst its impact on muscle protein synthesis is disputed. Thus, the aim of this study was to determine the effect of a mild physiological decrease in pH, by administration of ammonium chloride, on myofibrillar and mitochondrial protein synthesis, as well as associated molecular signaling events.

METHODS

Male Wistar rats were given either a placebo or ammonium chloride prior to a short interval training session. Rats were killed before exercise, immediately after exercise, or 3 h after exercise.

RESULTS

Myofibrillar (p = 0.036) fractional protein synthesis rates was increased immediately after exercise in the soleus muscle of the placebo group, but this effect was absent in the ammonium chloride group. However, in the gastrocnemius muscle NH4 Cl increased myofibrillar (p = 0.044) and mitochondrial protein synthesis (0 h after exercise p = 0.01; 3 h after exercise p = 0.003). This was accompanied by some small differences in protein phosphorylation and mRNA expression.

CONCLUSION

This study found ammonium chloride administration immediately prior to a single session of exercise in rats had differing effects on mitochondrial and myofibrillar protein synthesis rates in soleus (type I) and gastrocnemius (type II) muscle in rats.

Are periods of feeding and fasting protective during critical illness?

PURPOSE OF REVIEW

To review the mechanisms how intermittent feeding regimens could be beneficial in critically ill patients.

RECENT FINDINGS

Large randomized controlled trials (RCTs) have failed to demonstrate consistent benefit of early, enhanced nutritional support to critically ill patients, and some trials even found potential harm. Although speculative, the absence of a clear benefit could be explained by the continuous mode of feeding in these trials, since intermittent feeding regimens had health-promoting effects in healthy animals and humans through mechanisms that also appear relevant in critical illness. Potential protective mechanisms include avoidance of the muscle-full effect and improved protein synthesis, improved insulin sensitivity, better preservation of circadian rhythm, and fasting-induced stimulation of autophagy and ketogenesis. RCTs comparing continuous versus intermittent feeding regimens in critically ill patients have shown mixed results, albeit with different design and inclusion of relatively few patients. In all studies, the fasting interval was relatively short (4-6 h maximum), which may be insufficient to develop a full fasting response and associated benefits.

SUMMARY

These findings open perspectives for the design and clinical validation of intermittent feeding regimens for critically ill patients. The optimal mode and duration of the fasting interval, if any, remain unclear.

Interactions between Growth of Muscle and Stature: Mechanisms Involved and Their Nutritional Sensitivity to Dietary Protein: The Protein-Stat Revisited

Childhood growth and its sensitivity to dietary protein is reviewed within a Protein-Stat model of growth regulation. The coordination of growth of muscle and stature is a combination of genetic programming, and of two-way mechanical interactions involving the mechanotransduction of muscle growth through stretching by bone length growth, the core Protein-Stat feature, and the strengthening of bone through muscle contraction via the mechanostat. Thus, growth in bone length is the initiating event and this is always observed. Endocrine and cellular mechanisms of growth in stature are reviewed in terms of the growth hormone-insulin like growth factor-1 (GH-IGF-1) and thyroid axes and the sex hormones, which together mediate endochondral ossification in the growth plate and bone lengthening. Cellular mechanisms of muscle growth during development are then reviewed identifying (a) the difficulties posed by the need to maintain its ultrastructure during myofibre hypertrophy within the extracellular matrix and the concept of muscle as concentric "bags" allowing growth to be conceived as bag enlargement and filling, (b) the cellular and molecular mechanisms involved in the mechanotransduction of satellite and mesenchymal stromal cells, to enable both connective tissue remodelling and provision of new myonuclei to aid myofibre hypertrophy and (c) the implications of myofibre hypertrophy for protein turnover within the myonuclear domain. Experimental data from rodent and avian animal models illustrate likely changes in DNA domain size and protein turnover during developmental and stretch-induced muscle growth and between different muscle fibre types. Growth of muscle in male rats during adulthood suggests that "bag enlargement" is achieved mainly through the action of mesenchymal stromal cells. Current understanding of the nutritional regulation of protein deposition in muscle, deriving from experimental studies in animals and human adults, is reviewed, identifying regulation by amino acids, insulin and myofibre volume changes acting to increase both ribosomal capacity and efficiency of muscle protein synthesis via the mechanistic target of rapamycin complex 1 (mTORC1) and the phenomenon of a "bag-full" inhibitory signal has been identified in human skeletal muscle. The final section deals with the nutritional sensitivity of growth of muscle and stature to dietary protein in children. Growth in length/height as a function of dietary protein intake is described in the context of the breastfed child as the normative growth model, and the "Early Protein Hypothesis" linking high protein intakes in infancy to later adiposity. The extensive paediatric studies on serum IGF-1 and child growth are reviewed but their clinical relevance is of limited value for understanding growth regulation; a role in energy metabolism and homeostasis, acting with insulin to mediate adiposity, is probably more important. Information on the influence of dietary protein on muscle mass per se as opposed to lean body mass is limited but suggests that increased protein intake in children is unable to promote muscle growth in excess of that linked to genotypic growth in length/height. One possible exception is milk protein intake, which cohort and cross-cultural studies suggest can increase height and associated muscle growth, although such effects have yet to be demonstrated by randomised controlled trials.

High-Protein Plant-Based Diet Versus a Protein-Matched Omnivorous Diet to Support Resistance Training Adaptations: A Comparison Between Habitual Vegans and Omnivores

BACKGROUND

Acute protein turnover studies suggest lower anabolic response after ingestion of plant vs. animal proteins. However, the effects of an exclusively plant-based protein diet on resistance training-induced adaptations are under investigation.

OBJECTIVE

To investigate the effects of dietary protein source [exclusively plant-based vs. mixed diet] on changes in muscle mass and strength in healthy young men undertaking resistance training.

METHODS

Nineteen young men who were habitual vegans (VEG 26 ± 5 years; 72.7 ± 7.1 kg, 22.9 ± 2.3 kg/m²) and nineteen young men who were omnivores (OMN 26 ± 4 years; 73.3 ± 7.8 kg, 23.6 ± 2.3 kg/m²) undertook a 12-week, twice weekly, supervised resistance training program. Habitual protein intake was assessed at baseline and adjusted to 1.6 g kg^-1 day^-1 via supplemental protein (soy for VEG or whey for OMN). Dietary intake was monitored every four weeks during the intervention. Leg lean mass, whole muscle, and muscle fiber cross-sectional area (CSA), as well as leg-press 1RM were assessed before (PRE) and after the intervention (POST).

RESULTS

Both groups showed significant (all p < 0.05) PRE-to-POST increases in leg lean mass (VEG: 1.2 ± 1.0 kg; OMN: 1.2 ± 0.8 kg), rectus femoris CSA (VEG: 1.0 ± 0.6 cm²; OMN: 0.9 ± 0.5 cm²), vastus lateralis CSA (VEG: 2.2 ± 1.1 cm²; OMN: 2.8 ± 1.0 cm²), vastus lateralis muscle fiber type I (VEG: 741 ± 323 µm²; OMN: 677 ± 617 µm²) and type II CSA (VEG: 921 ± 458 µm²; OMN: 844 ± 638 µm²), and leg-press 1RM (VEG: 97 ± 38 kg; OMN: 117 ± 35 kg), with no between-group differences for any of the variables (all p > 0.05).

CONCLUSION

A high-protein (~ 1.6 g kg^-1 day^-1), exclusively plant-based diet (plant-based whole foods + soy protein isolate supplementation) is not different than a protein-matched mixed diet (mixed whole foods + whey protein supplementation) in supporting muscle strength and mass accrual, suggesting that protein source does not affect resistance training-induced adaptations in untrained young men consuming adequate amounts of protein.

CLINICAL TRIAL REGISTRATION

NCT03907059. April 8, 2019. Retrospectively registered.

Acute Effects of Cheddar Cheese Consumption on Circulating Amino Acids and Human Skeletal Muscle

Cheddar cheese is a protein-dense whole food and high in leucine content. However, no information is known about the acute blood amino acid kinetics and protein anabolic effects in skeletal muscle in healthy adults. Therefore, we conducted a crossover study in which men and women (n = 24; ~27 years, ~23 kg/m2) consumed cheese (20 g protein) or an isonitrogenous amount of milk. Blood and skeletal muscle biopsies were taken before and during the post absorptive period following ingestion. We evaluated circulating essential and non-essential amino acids, insulin, and free fatty acids and examined skeletal muscle anabolism by mTORC1 cellular localization, intracellular signaling, and ribosomal profiling. We found that cheese ingestion had a slower yet more sustained branched-chain amino acid circulation appearance over the postprandial period peaking at ~120 min. Cheese also modestly stimulated mTORC1 signaling and increased membrane localization. Using ribosomal profiling we found that, though both milk and cheese stimulated a muscle anabolic program associated with mTORC1 signaling that was more evident with milk, mTORC1 signaling persisted with cheese while also inducing a lower insulinogenic response. We conclude that Cheddar cheese induced a sustained blood amino acid and moderate muscle mTORC1 response yet had a lower glycemic profile compared to milk.

Role of Cachexia and Fragility in the Patient Candidate for Cardiac Surgery

Frailty is the major expression of accelerated aging and describes a decreased resistance to stressors, and consequently an increased vulnerability to additional diseases in elderly people. The vascular aging related to frail phenotype reflects the high susceptibility for cardiovascular diseases and negative postoperative outcomes after cardiac surgery. Sarcopenia can be considered a biological substrate of physical frailty. Malnutrition and physical inactivity play a key role in the pathogenesis of sarcopenia. We searched on Medline (PubMed) and Scopus for relevant literature published over the last 10 years and analyzed the strong correlation between frailty, sarcopenia and cardiovascular diseases in elderly patient. In our opinion, a right food intake and moderate intensity resistance exercise are mandatory in order to better prepare patients undergoing cardiac operation.

A collagen hydrolysate/milk protein-blend stimulates muscle anabolism equivalently to an isoenergetic milk protein-blend containing a greater quantity of essential amino acids in older men

Background & aims

Nutritional composition is key for skeletal muscle maintenance into older age. Yet the acute effects of collagen protein blended with other protein sources, in relation to skeletal muscle anabolism, are ill-defined. We investigated human muscle protein synthesis (MPS) responses to a 20 g blend of collagen protein hydrolysate + milk protein (CP+MP, 125 ml) oral nutritional supplement (ONS) vs. 20 g non-blended milk protein source (MP, 200 ml) ONS, in older adults.

Methods

Healthy older men (N = 8, 71±1 y, BMI: 27±1 kg·m⁻²) underwent a randomized trial of 20 g protein, from either a CP+MP blend (Fresubin®3.2 kcal DRINK), or a kcal-matched (higher in essential amino acids (EAA) ONS of MP alone. Vastus lateralis (VL) MPS and plasma AA were determined using stable isotope-tracer mass spectrometry; anabolic signaling was quantified via immuno-blotting in VL biopsies taken at baseline and 2/4 h after ONS feeding. Plasma insulin was measured via enzyme-linked immunosorbent assay (ELISA). Measures were taken at rest, after the feed (FED) and after the feed + exercise (FED-EX) conditions (unilateral leg exercise, 6 × 8, 75% 1-RM).

Results

MP resulted in a greater increase in plasma leucine (MP mean: 152 ± 6 μM, CP+MP mean: 113 ± 4 μM (Feed P < 0.001) and EAA (MP mean: 917 ± 25 μM, CP+MP mean: 786 ± 15 μM (Feed P < 0.01) than CP+MP. CP + MP increased plasma glycine (peak 385 ± 57 μM (P < 0.05)), proline (peak 323 ± 29 μM (P < 0.01)) and non-essential amino acids (NEAA) (peak 1621 ± 107 μM (P < 0.01)) with MP showing no increase. Plasma insulin increased in both trials (CP+MP: 58 ± 10 mU/mL (P < 0.01), MP: 42 ± 6 mU/mL (P < 0.01), with peak insulin greater with CP+MP vs. MP (P < 0.01). MPS demonstrated equivalent increases in response to CP+MP and MP under both FED (MP: 0.039 ± 0.005%/h to 0.081 ± 0.014%/h (P < 0.05), CP+MP: 0.042 ± 0.004%/h to 0.085 ± 0.007%/h (P < 0.05)) and FED-EX (MP: 0.039 ± 0.005%/h to 0.093 ± 0.013%/h (P < 0.01), CP+MP: 0.042 ± 0.004%/h to 0.105 ± 0.015%/h, (P < 0.01)) conditions. FED muscle p-mTOR fold-change from baseline increased to a greater extent with CP+MP vs. MP (P < 0.05), whilst FED-EX muscle p-eEF2 fold-change from baseline decreased to a greater extent with CP+MP vs. MP (P < 0.05); otherwise anabolic signaling responses were indistinguishable.

Conclusion

Fresubin®3.2 kcal DRINK, which contains a 20 g mixed blend of CP+MP, resulted in equivalent MPS responses to MP alone. Fresubin® 3.2 Kcal DRINK may provide a suitable alternative to MP for use in older adults and a convenient way to supplement calories and protein to improve patient adherence and mitigate muscle mass loss.

How to Overcome Anabolic Resistance in Dialysis-Treated Patients?

A current hypothesis is that dialysis-treated patients are "anabolic resistant" i. e., their muscle protein synthesis (MPS) response to anabolic stimuli is blunted, an effect which leads to muscle wasting and poor physical performance in aging and in several chronic diseases. The importance of maintaining muscle mass and MPS is often neglected in dialysis-treated patients; better than to describe mechanisms leading to energy-protein wasting, the aim of this narrative review is to suggest possible strategies to overcome anabolic resistance in this patient's category. Food intake, in particular dietary protein, and physical activity, are the two major anabolic stimuli. Unfortunately, dialysis patients are often aged and have a sedentary behavior, all conditions which per se may induce a state of "anabolic resistance." In addition, patients on dialysis are exposed to amino acid or protein deprivation during the dialysis sessions. Unfortunately, the optimal amount and formula of protein/amino acid composition in supplements to maximixe MPS is still unknown in dialysis patients. In young healthy subjects, 20 g whey protein maximally stimulate MPS. However, recent observations suggest that dialysis patients need greater amounts of proteins than healthy subjects to maximally stimulate MPS. Since unneccesary amounts of amino acids could stimulate ureagenesis, toxins and acid production, it is urgent to obtain information on the optimal dose of proteins or amino acids/ketoacids to maximize MPS in this patients' population. In the meantime, the issue of maintaining muscle mass and function in dialysis-treated CKD patients needs not to be overlooked by the kidney community.

The efficacy of essential amino acid supplementation for augmenting dietary protein intake in older adults: implications for skeletal muscle mass, strength and function

The primary aim of this review is to evaluate the efficacy of essential amino acid (EAA) supplementation as a strategy to increase dietary protein intake and improve muscle mass, strength and function in older adults. A sufficient daily protein intake is widely recognised to be fundamental for the successful management of sarcopenia in older undernourished adults. In practice, optimising protein intakes in older adults is complex, requiring consideration of the dose and amino acid composition (i.e. a complete EAA profile and abundant leucine content) of ingested protein on a per meal basis, alongside the age-related decline in appetite and the satiating properties of protein. Recent studies in older adults demonstrate that EAA-based supplements are non-satiating and can be administered alongside food to enhance the anabolic properties of a meal containing a suboptimal dose of protein; an effect magnified when combined with resistance exercise training. These findings support the notion that EAA supplementation could serve as an effective strategy to improve musculoskeletal health in older adults suffering from non-communicable diseases such as sarcopenia. Compliance is critical for the long-term success of complex interventions. Hence, aspects of palatability and desire to eat are important considerations regarding EAA supplementation. In conclusion, EAA-based supplements enriched with l-leucine offer an alternative strategy to whole protein sources to assist older adults in meeting protein recommendations. In practice, EAA supplements could be administered alongside meals of suboptimal protein content, or alternatively between meals on occasions when older adults achieve their per meal protein intake recommendations.

Exploring the Impact of Obesity on Skeletal Muscle Function in Older Age

Sarcopenia is of important clinical relevance for loss of independence in older adults. The prevalence of obesity in combination with sarcopenia ("sarcopenic-obesity") is increasing at a rapid rate. However, whilst the development of sarcopenia is understood to be multi-factorial and harmful to health, the role of obesity from a protective and damaging perspective on skeletal muscle in aging, is poorly understood. Specifically, the presence of obesity in older age may be accompanied by a greater volume of skeletal muscle mass in weight-bearing muscles compared with lean older individuals, despite impaired physical function and resistance to anabolic stimuli. Collectively, these findings support a potential paradox in which obesity may protect skeletal muscle mass in older age. One explanation for these paradoxical findings may be that the anabolic response to weight-bearing activity could be greater in obese vs. lean older individuals due to a larger mechanical stimulus, compensating for the heightened muscle anabolic resistance. However, it is likely that there is a complex interplay between muscle, adipose, and external influences in the aging process that are ultimately harmful to health in the long-term. This narrative briefly explores some of the potential mechanisms regulating changes in skeletal muscle mass and function in aging combined with obesity and the interplay with sarcopenia, with a particular focus on muscle morphology and the regulation of muscle proteostasis. In addition, whilst highly complex, we attempt to provide an updated summary for the role of obesity from a protective and damaging perspective on muscle mass and function in older age. We conclude with a brief discussion on treatment of sarcopenia and obesity and a summary of future directions for this research field.

Pathways regulating equine skeletal muscle protein synthesis respond in a dose-dependent manner to graded levels of protein intake

Activation of the mechanistic target of rapamycin (mTOR)-controlled anabolic signaling pathways in skeletal muscle of rodents and humans is responsive to the level of dietary protein supply, with maximal activation and rates of protein synthesis achieved with 0.2 to 0.4 g protein/kg body weight (BW). In horses, few data are available on the required level of dietary protein to maximize protein synthesis for maintenance and growth of skeletal muscle. To evaluate the effect of dietary protein level on muscle mTOR pathway activation, five mares received different amounts of a protein supplement that provided 0, 0.06, 0.125, 0.25, or 0.5 g of crude protein (CP)/kg BW per meal in a 5 × 5 Latin square design. On each sample day, horses were fasted overnight and were fed only their protein meal the following morning. A preprandial (0 min) and postprandial (90 min) blood sample was collected and a gluteus medius muscle sample was obtained 90 min after feeding the protein meal. Blood samples were analyzed for glucose, insulin, and amino acid concentrations. Activation of mTOR pathway components (mTOR and ribosomal protein S6 [rpS6]) in the muscle samples was measured by Western immunoblot analysis. Postprandial plasma glucose (P = 0.007) and insulin (P = 0.09) showed a quadratic increase, while total essential amino acid (P < 0.0001) concentrations increased linearly with the graded intake of the protein supplement. Activation of mTOR (P = 0.02) and its downstream target, rpS6 (P = 0.0008), increased quadratically and linearly in relation to the level of protein intake, respectively. Comparisons of individual doses showed no differences (P > 0.05) between the 0.25 and 0.5 g of protein intake for either mTOR or rpS6 activation, indicating that protein synthesis may have reached near maximal capacity around 0.25 g CP/kg BW. This is the first study to show that the activation of muscle protein synthetic pathways in horses is dose-dependent on the level of protein intake. Consumption of a moderate dose of high-quality protein resulted in near maximal muscle mTOR pathway activation in mature, sedentary horses.

Important determinants to take into account to optimize protein nutrition in the elderly: solutions to a complex equation

During ageing, skeletal muscle develops anabolic resistance towards the stimulation of protein synthesis induced by dietary amino acids. The stimulation of muscle protein synthesis after food intake remains insufficient, even with a protein intake recommended for healthy adults. This alteration is one of the mechanisms known to be responsible for the decrease of muscle mass and function during ageing, namely sarcopenia. Increasing dietary protein intake above the current RDA(0⋅83 g/kg/d) has been strongly suggested to overcome the anabolic resistance observed. It is also specified that the dietary protein ingested should be of good quality. A protein of good quality is a protein whose amino acid (AA) composition covers the requirement of each AA when ingested at the RDA. However, the biological value of proteins may vary among dietary sources in which AA composition could be unbalanced. In the present review, we suggest that the quality of a dietary protein is also related to several other determinants. These determinants include the speed of digestion of dietary proteins, the presence of specific AA, the food matrix in which the dietary proteins are included, the processes involved in the production of food products (milk gelation and cooking temperature), the energy supply and its nature, and the interaction between nutrients before ingestion. Particular attention is given to plant proteins for nutrition of the elderly. Finally, the timing of protein intake and its association with the desynchronized intake of energetic nutrients are discussed.

Dietary protein, exercise, ageing and physical inactivity: interactive influences on skeletal muscle proteostasis

Dietary protein is a pre-requisite for the maintenance of skeletal muscle mass; stimulating increases in muscle protein synthesis (MPS), via essential amino acids (EAA), and attenuating muscle protein breakdown, via insulin. Muscles are receptive to the anabolic effects of dietary protein, and in particular the EAA leucine, for only a short period (i.e. about 2-3 h) in the rested state. Thereafter, MPS exhibits tachyphylaxis despite continued EAA availability and sustained mechanistic target of rapamycin complex 1 signalling. Other notable characteristics of this 'muscle full' phenomenon include: (i) it cannot be overcome by proximal intake of additional nutrient signals/substrates regulating MPS; meaning a refractory period exists before a next stimulation is possible, (ii) it is refractory to pharmacological/nutraceutical enhancement of muscle blood flow and thus is not induced by muscle hypo-perfusion, (iii) it manifests independently of whether protein intake occurs in a bolus or intermittent feeding pattern, and (iv) it does not appear to be dependent on protein dose per se. Instead, the main factor associated with altering muscle full is physical activity. For instance, when coupled to protein intake, resistance exercise delays the muscle full set-point to permit additional use of available EAA for MPS to promote muscle remodelling/growth. In contrast, ageing is associated with blunted MPS responses to protein/exercise (anabolic resistance), while physical inactivity (e.g. immobilisation) induces a premature muscle full, promoting muscle atrophy. It is crucial that in catabolic scenarios, anabolic strategies are sought to mitigate muscle decline. This review highlights regulatory protein turnover interactions by dietary protein, exercise, ageing and physical inactivity.

Testosterone supplementation upregulates androgen receptor expression and translational capacity during severe energy deficit

Testosterone supplementation during energy deficit promotes whole body lean mass accretion, but the mechanisms underlying that effect remain unclear. To elucidate those mechanisms, skeletal muscle molecular adaptations were assessed from muscle biopsies collected before, 1 h, and 6 h after exercise and a mixed meal (40 g protein, 1 h postexercise) following 14 days of weight maintenance (WM) and 28 days of an exercise- and diet-induced 55% energy deficit (ED) in 50 physically active nonobese men treated with 200 mg testosterone enanthate/wk (TEST) or placebo (PLA) during the ED. Participants (n = 10/group) exhibiting substantial increases in leg lean mass and total testosterone (TEST) were compared with those exhibiting decreases in both of these measures (PLA). Resting androgen receptor (AR) protein content was higher and fibroblast growth factor-inducible 14 (Fn14), IL-6 receptor (IL-6R), and muscle ring-finger protein-1 gene expression was lower in TEST vs. PLA during ED relative to WM (P < 0.05). Changes in inflammatory, myogenic, and proteolytic gene expression did not differ between groups after exercise and recovery feeding. Mechanistic target of rapamycin signaling (i.e., translational efficiency) was also similar between groups at rest and after exercise and the mixed meal. Muscle total RNA content (i.e., translational capacity) increased more during ED in TEST than PLA (P < 0.05). These findings indicate that attenuated proteolysis at rest, possibly downstream of AR, Fn14, and IL-6R signaling, and increased translational capacity, not efficiency, may drive lean mass accretion with testosterone administration during energy deficit.

Protein Intake and Frailty: A Matter of Quantity, Quality, and Timing

Frailty is a geriatric syndrome that refers to a state of reduced resiliency to stressful events that occurs in response to physiological and/or psychosocial detriments. Frailty is a predictor of poor prognosis, given that frail older adults are at higher risk of many adverse health-related events. Hence, the identification of potential strategies to prevent the development and progression of frailty is of extreme importance for avoiding its negative outcomes. An adequate protein consumption is advocated as a possible intervention for the management of frailty in older adults due to its effects on muscle mass and physical function. However, empirical evidence is still needed to support this proposition. On the other hand, substantial evidence from observational studies has provided important information on the association between frailty and dietary protein-related parameters. Here, we provide a narrative review of the current literature regarding the association between protein intake (amount (how much?), quality (what type?), and distribution across meals (when?)) and frailty-related parameters. The ultimate aim of this work is to offer practical, evidence-based indications to healthcare professionals responsible for the care of frail older adults.

The daytime feeding frequency affects appetite-regulating hormones, amino acids, physical activity, and respiratory quotient, but not energy expenditure, in adult cats fed regimens for 21 days

The effects of feeding frequency on postprandial response of circulating appetite-regulating hormones, insulin, glucose and amino acids, and on physical activity, energy expenditure, and respiratory quotient were studied in healthy adult cats. Two experiments were designed as a 2 x 3 replicated incomplete Latin square design. Eight cats, with an average body weight (BW) of 4.34 kg ± 0.04 and body condition score (BCS) of 5.4 ± 1.4 (9 point scale), were fed isocaloric amounts of a commercial adult maintenance canned cat food either once (0800 h) or four times daily (0800 h, 1130 h, 1500 h, 1830 h). Study 1 consisted of three 21-d periods. On day 14, two fasted and 11 postprandial blood samples were collected over 24 hours to measure plasma concentrations of ghrelin, GLP-1, GIP, leptin, PYY, insulin and amino acids, and whole blood glucose. Physical activity was monitored from day 15 to 21 of each period. In Study 2 indirect calorimetry was performed on the last day of each period. Body weight was measured weekly and feed intake recorded daily in both experiments. No effect of feeding regimen on BW was detected. Cats eating four times daily had lesser plasma concentrations of GIP and GLP-1 (P<0.05) and tended to have lesser plasma PYY concentrations (P<0.1). Plasma leptin and whole blood glucose concentrations did not differ between regimens (P>0.1). Cats fed once daily had a greater postprandial plasma amino acid response, and greater plasma ghrelin and insulin concentrations (P<0.05). Physical activity was greater in cats fed four times (P<0.05), though energy expenditure was similar between treatments at fasting and in postprandial phases. Finally, cats eating one meal had a lower fasting respiratory quotient (P<0.05). Overall, these data indicate that feeding once a day may be a beneficial feeding management strategy for indoor cats to promote satiation and lean body mass.

Animal, Plant, Collagen and Blended Dietary Proteins: Effects on Musculoskeletal Outcomes

Dietary protein is critical for the maintenance of musculoskeletal health, where appropriate intake (i.e., source, dose, timing) can mitigate declines in muscle and bone mass and/or function. Animal-derived protein is a potent anabolic source due to rapid digestion and absorption kinetics stimulating robust increases in muscle protein synthesis and promoting bone accretion and maintenance. However, global concerns surrounding environmental sustainability has led to an increasing interest in plant- and collagen-derived protein as alternative or adjunct dietary sources. This is despite the lower anabolic profile of plant and collagen protein due to the inferior essential amino acid profile (e.g., lower leucine content) and subordinate digestibility (versus animal). This review evaluates the efficacy of animal-, plant- and collagen-derived proteins in isolation, and as protein blends, for augmenting muscle and bone metabolism and health in the context of ageing, exercise and energy restriction.

Glucagon-like peptide 1 infusions overcome anabolic resistance to feeding in older human muscle

Background

Despite its known insulin‐independent effects, glucagon‐like peptide‐1 (GLP‐1) role in muscle protein turnover has not been explored under fed‐state conditions or in the context of older age, when declines in insulin sensitivity and protein anabolism, as well as losses of muscle mass and function, occur.

Methods

Eight older‐aged men (71 ± 1 year, mean ± SEM) were studied in a crossover trial. Baseline measures were taken over 3 hr, prior to a 3 hr postprandial insulin (~30 mIU ml⁻¹) and glucose (7–7.5 mM) clamp, alongside I.V. infusions of octreotide and Vamin 14 (±infusions of GLP‐1). Four muscle biopsies were taken, and muscle protein turnover was quantified via incorporation of ¹³C₆ phenylalanine and arteriovenous balance kinetics, using mass spectrometry. Leg macro‐ and microvascular flow was assessed via ultrasound and anabolic signalling by immunoblotting. GLP‐1 and insulin were measured by ELISA.

Results

GLP‐1 augmented muscle protein synthesis (MPS; fasted: 0.058 ± 0.004% hr⁻¹ vs. postprandial: 0.102 ± 0.005% hr⁻¹, p < 0.01), in comparison with non‐GLP‐1 trials. Muscle protein breakdown (MPB) was reduced throughout clamp period, while net protein balance across the leg became positive in both groups. Total femoral leg blood flow was unchanged by the clamp; however, muscle microvascular blood flow (MBF) was significantly elevated in both groups, and to a significantly greater extent in the GLP‐1 group (MBF: 5 ± 2 vs. 1.9 ± 1 fold change +GLP‐1 and −GLP‐1, respectively, p < 0.01). Activation of the Akt‐mTOR signalling was similar across both trials.

Conclusion

GLP‐1 infusion markedly enhanced postprandial microvascular perfusion and further stimulated muscle protein metabolism, primarily through increased MPS, during a postprandial insulin hyperaminoacidaemic clamp.

Protein delivery in intermittent and continuous enteral nutrition with a protein-rich formula in critically ill patients-a protocol for the prospective randomized controlled proof-of-concept Protein Bolus Nutrition (Pro BoNo) study

Background

Critically ill patients rapidly develop muscle wasting resulting in sarcopenia, long-term disability and higher mortality. Bolus nutrition (30–60 min period), whilst having a similar incidence of aspiration as continuous feeding, seems to provide metabolic benefits through increased muscle protein synthesis due to higher leucine peaks.

To date, clinical evidence on achievement of nutritional goals and influence of bolus nutrition on skeletal muscle metabolism in ICU patients is lacking. The aim of the Pro BoNo study (Protein Bolus Nutrition) is to compare intermittent and continuous enteral feeding with a specific high-protein formula. We hypothesise that target quantity of protein is reached earlier (within 36 h) by an intermittent feeding protocol with a favourable influence on muscle protein synthesis.

Methods

Pro BoNo is a prospective randomised controlled study aiming to compare the impact of intermittent and continuous enteral feeding on preventing muscle wasting in 60 critically ill patients recruited during the first 48 h after ICU admission. The primary outcome measure is the time until the daily protein target (≥ 1.5 g protein/kg bodyweight/24 h) is achieved. Secondary outcome measures include tolerance of enteral feeding and evolution of glucose, urea and IGF-1. Ultrasound and muscle biopsy of the quadriceps will be performed.

Discussion

The Basel Pro BoNo study aims to collect innovative data on the effect of intermittent enteral feeding of critically ill patients on muscle wasting.

Trial registration

ClinicalTrials.gov NCT03587870. Registered on July 16, 2018. Swiss National Clinical Trials Portal SNCTP000003234. Last updated on July 24, 2019.

Muscle Protein Synthesis and Whole-Body Protein Turnover Responses to Ingesting Essential Amino Acids, Intact Protein, and Protein-Containing Mixed Meals with Considerations for Energy Deficit

Protein intake recommendations to optimally stimulate muscle protein synthesis (MPS) are derived from dose-response studies examining the stimulatory effects of isolated intact proteins (e.g., whey, egg) on MPS in healthy individuals during energy balance. Those recommendations may not be adequate during periods of physiological stress, specifically the catabolic stress induced by energy deficit. Providing supplemental intact protein (20–25 g whey protein, 0.25–0.3 g protein/kg per meal) during strenuous military operations that elicit severe energy deficit does not stimulate MPS-associated anabolic signaling or attenuate lean mass loss. This occurs likely because a greater proportion of the dietary amino acids consumed are targeted for energy-yielding pathways, whole-body protein synthesis, and other whole-body essential amino acid (EAA)-requiring processes than the proportion targeted for MPS. Protein feeding formats that provide sufficient energy to offset whole-body energy and protein-requiring demands during energy deficit and leverage EAA content, digestion, and absorption kinetics may optimize MPS under these conditions. Understanding the effects of protein feeding format-driven alterations in EAA availability and subsequent changes in MPS and whole-body protein turnover is required to design feeding strategies that mitigate the catabolic effects of energy deficit. In this manuscript, we review the effects, advantages, disadvantages, and knowledge gaps pertaining to supplemental free-form EAA, intact protein, and protein-containing mixed meal ingestion on MPS. We discuss the fundamental role of whole-body protein balance and highlight the importance of comprehensively assessing whole-body and muscle protein kinetics when evaluating the anabolic potential of varying protein feeding formats during energy deficit.

The Potential Role of Fish-Derived Protein Hydrolysates on Metabolic Health, Skeletal Muscle Mass and Function in Ageing

Fish protein represents one of the most widely consumed dietary protein sources by humans. The processing of material from the fishing industry generates substantial unexploited waste products, many of which possess high biological value. Protein hydrolysates, such as fish protein hydrolysates (FPH), containing predominantly di- and tripeptides, are more readily absorbed than free amino acids and intact protein. Furthermore, in animal models, FPH have been shown to possess numerous beneficial properties for cardiovascular, neurological, intestinal, renal, and immune health. Ageing is associated with the loss of skeletal muscle mass and function, as well as increased oxidative stress, compromised vascularisation, neurological derangements, and immunosenescence. Thus, there appears to be a potential application for FPH in older persons as a high-quality protein source that may also confer additional health benefits. Despite this, there remains a dearth of information concerning the impact of FPH on health outcomes in humans. The limited evidence from human interventional trials suggests that FPH may hold promise for supporting optimal body composition and maintaining gut integrity. FPH also provide a high-quality source of dietary protein without negatively impacting on subjective appetite perceptions or regulatory hormones. Further studies are needed to assess the impact and utility of FPH on skeletal muscle health in older persons, ideally comparing FPH to ‘established’ protein sources or a non-bioactive, nitrogen-matched control. In particular, the effects of acute and chronic FPH consumption on post-exercise aminoacidaemia, skeletal muscle protein synthesis, and intramyocellular anabolic signalling in older adults are worthy of investigation. FPH may represent beneficial and sustainable alternative sources of high-quality protein to support skeletal muscle health and anabolism in ageing, without compromising appetite and subsequent energy intake.

The Effects of Timing of a Leucine-Enriched Amino Acid Supplement on Body Composition and Physical Function in Stroke Patients: A Randomized Controlled Trial

The combination of exercise and nutritional intervention is widely used for stroke patients, as well as frail or sarcopenic older persons. As previously shown, supplemental branched chain amino acids (BCAAs) or protein to gain muscle mass has usually been given just after exercise. This study investigated the effect of the timing of supplemental BCAAs with exercise intervention on physical function in stroke patients. The participants were randomly assigned to two groups based on the timing of supplementation: breakfast (n = 23) and post-exercise (n = 23). The supplement in the breakfast group was provided at 08:00 with breakfast, and in the post-exercise group it was provided just after the exercise session in the afternoon at 14:00-18:00. In both groups, the exercise intervention was performed with two sessions a day for two months. The main effects were observed in body fat mass (p = 0.02, confidence interval (CI): 13.2-17.7), leg press strength (p = 0.04, CI: 94.5-124.5), and Berg balance scale (p = 0.03, CI: 41.6-52.6), but no interaction with intake timing was observed. Although the effect of the timing of supplementation on skeletal muscle mass was similar in both groups, BCAA intake with breakfast was effective for improving physical performance and decreasing body fat mass. The results suggest that a combination of BCAA intake with breakfast and an exercise program was effective for promoting rehabilitation of post-stroke patients.

The Role of Nutri(epi)genomics in Achieving the Body's Full Potential in Physical Activity

Physical activity represents a powerful tool to achieve optimal health. The overall activation of several molecular pathways is associated with many beneficial effects, mainly converging towards a reduced systemic inflammation. Not surprisingly, regular activity can contribute to lowering the “epigenetic age”, acting as a modulator of risk toward several diseases and enhancing longevity. Behind this, there are complex molecular mechanisms induced by exercise, which modulate gene expression, also through epigenetic modifications. The exercise-induced epigenetic imprint can be transient or permanent and contributes to the muscle memory, which allows the skeletal muscle adaptation to environmental stimuli previously encountered. Nutrition, through key macro- and micronutrients with antioxidant properties, can play an important role in supporting skeletal muscle trophism and those molecular pathways triggering the beneficial effects of physical activity. Nutrients and antioxidant food components, reversibly altering the epigenetic imprint, have a big impact on the phenotype. This assigns a role of primary importance to nutri(epi)genomics, not only in optimizing physical performance, but also in promoting long term health. The crosstalk between physical activity and nutrition represents a major environmental pressure able to shape human genotypes and phenotypes, thus, choosing the right combination of lifestyle factors ensures health and longevity.

Report of a member-led meeting: how stable isotope techniques can enhance human nutrition research

A Nutrition Society member-led meeting was held on 9 January 2020 at The University of Surrey, UK. Sixty people registered for the event, and all were invited to participate, either through chairing a session, presenting a '3 min lightning talk' or by presenting a poster. The meeting consisted of an introduction to the topic by Dr Barbara Fielding, with presentations from eight invited speakers. There were also eight lightning talks and a poster session. The meeting aimed to highlight recent research that has used stable isotope tracer techniques to understand human metabolism. Such studies have irrefutably shaped our current understanding of metabolism and yet remain a mystery to many. The meeting aimed to de-mystify their use in nutrition research.

Amino Acid Plasma Profiles from a Prolonged-Release Protein Substitute for Phenylketonuria: A Randomized, Single-Dose, Four-Way Crossover Trial in Healthy Volunteers

Several disorders of amino acid (AA) metabolism are treated with a protein-restricted diet supplemented with specific AA mixtures. Delivery kinetics impacts AA absorption and plasma concentration profiles. We assessed plasma profiles after ingestion of an AA mixture engineered to prolong AA absorption with Physiomimic Technology^TM (Test) in a randomized, single-dose, four-way crossover trial in healthy volunteers (Trial Registration: ISRCTN11016729). In a two-step hypothesis, the primary endpoints were (i) significant reduction in peak plasma concentrations (C_max) of essential amino acids (EAAs) while (ii) maintaining EAA bioavailability (AUC_{0-300 min}) compared to a free AA mixture (Reference). Secondary endpoints included effects on plasma profiles of other AA groups and effects on several metabolic markers. Thirty subjects completed the study. Both co-primary endpoints were met: C_max for EAAs was 27% lower with the Test product compared to the Reference product (ratio, 0.726, p < 0.0001); overall plasma EAA levels from the two AA mixtures was within the pre-specified bioequivalence range (AUC_0-300min ratio, 0.890 (95% CI: 0.865, 0.915)). These findings were supported by the results of secondary endpoints. Prolongation of AA absorption was associated with modulation of several metabolic markers. It will be important to understand whether this can improve the long-term management of disorders of AA metabolism.

Contemporary stable isotope tracer approaches: Insights into skeletal muscle metabolism in health and disease

NEW FINDINGS

What is the topic of this review? This review discusses the application of new stable isotope tracer techniques in understanding the control of skeletal muscle mass. What advances does it highlight? This review highlights current advances in stable isotope tracer techniques through their combination with high-throughput proteomics technologies.

ABSTRACT

Beyond its primary locomotory and key structural functions, skeletal muscle provides additional vital roles for maintenance of metabolic health, acting as a storage point for glucose and intramuscular lipids for energy production, alongside being the largest reservoir for amino acids in the body. Therefore, maintenance of muscle mass is key to the promotion of health and well-being across the lifespan and in several disease states. As such, when skeletal muscle is lost, in either clinical (cancer, organ failure etc.) or non-clinical (ageing, inactivity) situations, there are potentially devastating consequences attached, with robust links existing between muscle mass loss and mortality. Great efforts are being made to reverse or slow muscle mass declines in health and disease, through combinations of lifestyle changes and nutritional and/or pharmaceutical intervention. However, despite this comprehensive research effort, the underlying metabolic and molecular mechanisms have yet to be defined properly. However, with the rapid acceleration of analytical developments over recent years, the application of stable isotope tracers to the study of human muscle metabolism is providing unique insights into the mechanisms controlling skeletal muscle loss and allowing more targeted therapeutic strategies to be developed. The aim of this review is to highlight the technical breakthroughs in our understanding of muscle wasting in health and disease and how future directions and developments incorporating 'omics' with stable isotope tracers will allow for a more personalized and stratified therapeutic approach.

Effect of Intermittent or Continuous Feed on Muscle Wasting in Critical Illness: A Phase 2 Clinical Trial

BACKGROUND

Acute skeletal muscle wasting in critical illness is associated with excess morbidity and mortality. Continuous feeding may suppress muscle protein synthesis as a result of the muscle-full effect, unlike intermittent feeding, which may ameliorate it.

RESEARCH QUESTION

Does intermittent enteral feed decrease muscle wasting compared with continuous feed in critically ill patients?

STUDY DESIGN AND METHODS

In a phase 2 interventional single-blinded randomized controlled trial, 121 mechanically ventilated adult patients with multiorgan failure were recruited following prospective informed consultee assent. They were randomized to the intervention group (intermittent enteral feeding from six 4-hourly feeds per 24 h, n = 62) or control group (standard continuous enteral feeding, n = 59). The primary outcome was 10-day loss of rectus femoris muscle cross-sectional area determined by ultrasound. Secondary outcomes included nutritional target achievements, plasma amino acid concentrations, glycemic control, and physical function milestones.

RESULTS

Muscle loss was similar between arms (-1.1% [95% CI, -6.1% to -4.0%]; P = .676). More intermittently fed patients received 80% or more of target protein (OR, 1.52 [1.16-1.99]; P < .001) and energy (OR, 1.59 [1.21-2.08]; P = .001). Plasma branched-chain amino acid concentrations before and after feeds were similar between arms on trial day 1 (71 μM [44-98 μM]; P = .547) and trial day 10 (239 μM [33-444 μM]; P = .178). During the 10-day intervention period the coefficient of variation for glucose concentrations was higher with intermittent feed (17.84 [18.6-20.4]) vs continuous feed (12.98 [14.0-15.7]; P < .001). However, days with reported hypoglycemia and insulin usage were similar in both groups. Safety profiles, gastric intolerance, physical function milestones, and discharge destinations did not differ between groups.

INTERPRETATION

Intermittent feeding in early critical illness is not shown to preserve muscle mass in this trial despite resulting in a greater achievement of nutritional targets than continuous feeding. However, it is feasible and safe.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT02358512; URL: www.clinicaltrials.gov.

Exercise and physical activity in cirrhosis: opportunities or perils

Reduced exercise capacity and impaired physical performance are observed in nearly all patients with liver cirrhosis. Physical activity and exercise are physiological anabolic stimuli that can reverse dysregulated protein homeostasis or proteostasis and potentially increase muscle mass and contractile function in healthy subjects. Cirrhosis is a state of anabolic resistance, and unlike the beneficial responses to exercise reported in physiological states, there are few systematic studies evaluating the response to exercise in cirrhosis. Hyperammonemia is a mediator of the liver-muscle axis with net skeletal muscle ammonia uptake in cirrhosis causing signaling perturbations, mitochondrial dysfunction with decreased ATP content, modifications of contractile proteins, and impaired ribosomal function, all of which contribute to anabolic resistance in cirrhosis and have the potential to impair the beneficial responses to exercise. English language-publications in peer-reviewed journals that specifically evaluated the impact of exercise in cirrhosis were reviewed. Most studies evaluated responses to endurance exercise, and readouts included peak or maximum oxygen utilization, grip strength, and functional capacity. Endurance exercise for up to 12 wk is clinically tolerated in well-compensated cirrhosis. Data on the safety of resistance exercise are conflicting. Nutritional supplements enhance the benefits of exercise in healthy subjects but have not been evaluated in cirrhosis. Whether the beneficial physiological responses with endurance exercise and increase in muscle mass with resistance exercise that occur in healthy subjects also occur in cirrhotics is not known. Specific organ-system responses, changes in body composition, or improved long-term clinical outcomes with exercise in cirrhosis need evaluation.

The effect of sleep restriction, with or without high-intensity interval exercise, on myofibrillar protein synthesis in healthy young men

Key points

Sleep restriction has previously been associated with the loss of muscle mass in both human and animal models.

The rate of myofibrillar protein synthesis (MyoPS) is a key variable in regulating skeletal muscle mass and can be increased by performing high‐intensity interval exercise (HIIE), although the effect of sleep restriction on MyoPS is unknown.

In the present study, we demonstrate that participants undergoing a sleep restriction protocol (five nights, with 4 h in bed each night) had lower rates of skeletal muscle MyoPS; however, rates of MyoPS were maintained at control levels by performing HIIE during this period.

Our data suggest that the lower rates of MyoPS in the sleep restriction group may contribute to the detrimental effects of sleep loss on muscle mass and that HIIE may be used as an intervention to counteract these effects.

Abstract

The present study aimed to investigate the effect of sleep restriction, with or without high‐intensity interval exercise (HIIE), on the potential mechanisms underpinning previously‐reported sleep‐loss‐induced reductions to muscle mass. Twenty‐four healthy, young men underwent a protocol consisting of two nights of controlled baseline sleep and a five‐night intervention period. Participants were allocated into one of three parallel groups, matched for age, V˙O2peak, body mass index and habitual sleep duration; a normal sleep (NS) group [8 h time in bed (TIB) each night], a sleep restriction (SR) group (4 h TIB each night), and a sleep restriction and exercise group (SR+EX, 4 h TIB each night, with three sessions of HIIE). Deuterium oxide was ingested prior to commencing the study and muscle biopsies obtained pre‐ and post‐intervention were used to assess myofibrillar protein synthesis (MyoPS) and molecular markers of protein synthesis and degradation signalling pathways. MyoPS was lower in the SR group [fractional synthetic rate (% day^–1), mean ± SD, 1.24 ± 0.21] compared to both the NS (1.53 ± 0.09) and SR+EX groups (1.61 ± 0.14) (P < 0.05). However, there were no changes in the purported regulators of protein synthesis (i.e. p‐AKT^ser473 and p‐mTOR^ser2448) and degradation (i.e. Foxo1/3 mRNA and LC3 protein) in any group. These data suggest that MyoPS is acutely reduced by sleep restriction, although MyoPS can be maintained by performing HIIE. These findings may explain the sleep‐loss‐induced reductions in muscle mass previously reported and also highlight the potential therapeutic benefit of HIIE to maintain myofibrillar remodelling in this context.

Sleep restriction has previously been associated with the loss of muscle mass in both human and animal models.

The rate of myofibrillar protein synthesis (MyoPS) is a key variable in regulating skeletal muscle mass and can be increased by performing high‐intensity interval exercise (HIIE), although the effect of sleep restriction on MyoPS is unknown.

In the present study, we demonstrate that participants undergoing a sleep restriction protocol (five nights, with 4 h in bed each night) had lower rates of skeletal muscle MyoPS; however, rates of MyoPS were maintained at control levels by performing HIIE during this period.

Our data suggest that the lower rates of MyoPS in the sleep restriction group may contribute to the detrimental effects of sleep loss on muscle mass and that HIIE may be used as an intervention to counteract these effects.

Nutritional Recommendations for Physique Athletes

The popularity of physique sports is increasing, yet there are currently few comprehensive nutritional guidelines for these athletes. Physique sport now encompasses more than just a short phase before competition and offseason guidelines have recently been published. Therefore, the goal of this review is to provide an extensive guide for male and female physique athletes in the contest preparation and recovery period. As optimal protein intake is largely related to one’s skeletal muscle mass, current evidence supports a range of 1.8-2.7 g/kg. Furthermore, as a benefit from having adequate carbohydrate to fuel performance and activity, low-end fat intake during contest preparation of 10-25% of calories allows for what calories remain in the “energy budget” to come from carbohydrate to mitigate the negative impact of energy restriction and weight loss on training performance. For nutrient timing, we recommend consuming four or five protein boluses per day with one consumed near training and one prior to sleep. During competition periods, slower rates of weight loss (≤0.5% of body mass per week) are preferable for attenuating the loss of fat-free mass with the use of intermittent energy restriction strategies, such as diet breaks and refeeds, being possibly beneficial. Additionally, physiological and psychological factors are covered, and potential best-practice guidelines are provided for disordered eating and body image concerns since physique athletes present with higher incidences of these issues, which may be potentially exacerbated by certain traditional physique practices. We also review common peaking practices, and the critical transition to the post-competition period.

Differential regulation of mTORC1 activation by leucine and β-hydroxy-β-methylbutyrate in skeletal muscle of neonatal pigs

Leucine (Leu) and its metabolite β-hydroxy-β-methylbutyrate (HMB) stimulate mechanistic target of rapamycin (mTOR) complex 1 (mTORC1)-dependent protein synthesis in the skeletal muscle of neonatal pigs. This study aimed to determine whether HMB and Leu utilize common nutrient-sensing mechanisms to activate mTORC1. In study 1, neonatal pigs were fed one of five diets for 24 h: low protein (LP), high protein (HP), or LP supplemented with 4 (LP+HMB4), 40 (LP+HMB40), or 80 (LP+HMB80) μmol HMB·kg body wt^-1·day^-1. In study 2, neonatal pigs were fed for 24 h: LP, LP supplemented with Leu (LP+Leu), or HP diets delivering 9, 18, and 18 mmol Leu·kg body wt^-1·day^-1, respectively. The upstream signaling molecules that regulate mTORC1 activity were analyzed. mTOR phosphorylation on Ser2448 and Ser2481 was greater in LP+HMB40, LP+HMB80, and LP+Leu than in LP and greater in HP than in HMB-supplemented groups (P < 0.05), whereas HP and LP+Leu were similar. Rheb-mTOR complex formation was lower in LP than in HP (P < 0.05), with no enhancement by HMB or Leu supplementation. The Sestrin2-GATOR2 complex was more abundant in LP than in HP and was reduced by Leu (P < 0.05) but not HMB supplementation. RagA-mTOR and RagC-mTOR complexes were higher in LP+Leu and HP than in LP and HMB groups (P < 0.05). There were no treatment differences in RagB-SH3BP4, Vps34-LRS, and RagD-LRS complex abundances. Phosphorylation of Erk1/2 and TSC2, but not AMPK, was lower in LP than HP (P < 0.05) and unaffected by HMB or Leu supplementation. Our results demonstrate that HMB stimulates mTORC1 activation in neonatal muscle independent of the leucine-sensing pathway mediated by Sestrin2 and the Rag proteins.NEW & NOTEWORTHY Dietary supplementation with either leucine or its metabolite β-hydroxy-β-methylbutyrate (HMB) stimulates protein synthesis in skeletal muscle of the neonatal pig. Our results demonstrate that both leucine and HMB stimulate mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) phosphorylation in neonatal muscle. This leucine-stimulated process involves dissociation of the Sestrin2-GATOR2 complex and increased binding of Rag A/C to mTOR. However, HMB's activation of mTORC1 is independent of this leucine-sensing pathway.

A word of caution against excessive protein intake

Dietary protein is crucial for human health because it provides essential amino acids for protein synthesis. In addition, dietary protein is more satiating than carbohydrate and fat. Accordingly, many people consider the protein content when purchasing food and beverages and report 'trying to eat more protein'. The global market for protein ingredients is projected to reach approximately US$90 billion by 2021, largely driven by the growing demand for protein-fortified food products. This Perspective serves as a caution against the trend of protein-enriched diets and provides an evidence-based counterpoint that underscores the potential adverse public health consequences of high protein intake.

Ingestion of a Pre-bedtime Protein Containing Beverage Prevents Overnight Induced Negative Whole Body Protein Balance in Healthy Middle-Aged Men: A Randomized Trial

Age related muscle wasting leads to overall reductions of lean body mass, reduced muscle strength, and muscle function resulting in compromised quality of life. Utilizing novel nutritional strategies to attenuate such losses is of great importance in elderly individuals. We aimed to test if a complete dietary supplement containing 25 g of milk proteins and ingested in the evening before bed would improve protein metabolism in terms of whole body protein balance over a 10 h overnight period following ingestion of the test drink in healthy middle-aged male subjects. In addition we also assessed the rates of muscle protein synthesis during the second half of the night in order to see if previously reported extended amino acidemia during sleep results in increased rates of muscle protein synthesis. Seventeen healthy middle-aged male subjects (59.4 ± 3.2 year) consumed a dietary supplement drink at 21:00 containing either 25 g milk protein concentrate, 25 g maltodextrin, 7.75 g canola oil (treatment group), or an isocaloric protein void drink (placebo group). Muscle protein synthesis was assessed from a muscle biopsy following the continuous intravenous infusion of ¹³C-phenylalanine for 5 h (from 03:00 to 08:00). Whole body protein balance was greater in the treatment group (−0.13 ± 11.30 g prot/10 h) compared to placebo (−12.22 ± 6.91 g prot/10 h) (P ≤ 0.01). In contrast, no changes were observed on rates of muscle protein synthesis during the second half of the night. Ingestion of a dietary supplement containing 25 g of milk proteins significantly reduced the negative protein balance observed during the night. Therefore, pre-bedtime protein ingestion may attenuate overnight losses of lean tissue in healthy elderly men. Despite increases in aminoacidemia during the second part of the night, no changes were observed in the rates of muscle protein synthesis during this time.

Clinical Trial Registration:www.ClinicalTrials.gov, identifier: NCT02041143.

Dietary Aronia melanocarpa extract enhances mTORC1 signaling, but has no effect on protein synthesis and protein breakdown-related signaling, in response to resistance exercise in rat skeletal muscle

BACKGROUND

Ursolic acid altered muscle protein metabolism in normal and resting conditions after acute resistance exercise, suggesting that eating fruits rich in ursolic acid could enhance muscle protein synthesis and decrease muscle degradation. Aronia melanocarpa, a member of the family Rosaceae and native to North America and Eastern Canada, is rich in ursolic acid. In this study, we examined the effects of A. melanocarpa extract (AME) supplementation on the mTORC1 signaling pathway and muscle degradation-related factors in rats, both alone and in combination with resistance exercise.

METHODS

Male Sprague-Dawley rats were divided into AME and normal chow (NOR) groups. AME group was fed chow providing a dose of 3 g/kg of AME and 115 mg/kg of ursolic acid for 7 days, whereas NOR rats were fed normal powder chow. The right gastrocnemius muscle of each animal was isometrically exercised (5 sets of ten 3-s contractions, with a 7-s interval between contractions and 3-min rest intervals between sets), while the left gastrocnemius muscle served as an internal control. Western blotting and real-time polymerase chain reaction were used to assess expression of factors involved in the mTORC1 signaling pathway and muscle degradation.

RESULTS

At 1 h after resistance exercise, phosphorylation of ERK1/2 was significantly increased by AME consumption. At 6 h after resistance exercise, AME consumption significantly increased the phosphorylation of Akt, p70S6K, rpS6, and AMPK. It also increased MAFbx expression. Furthermore, AME significantly increased the phosphorylation of p70S6K and rpS6 in response to resistance exercise. However, AME did not increase muscle protein synthesis (MPS) after resistance exercise. AME did not affect the expression of any of the mediators of protein degradation, with the exception of MAFbx.

CONCLUSIONS

Dietary AME enhanced mTORC1 activation in response to resistance exercise without increasing MPS. Moreover, it neither accelerated muscle protein degradation nor otherwise negatively affected protein metabolism. Further study is needed to clarify the effect of the combination of AME and chronic resistance training on muscle hypertrophy.