Whole-body protein kinetic models to quantify the anabolic response to dietary protein consumption

Common questions and misconceptions about protein supplementation: what does the scientific evidence really show?

Protein supplementation often refers to increasing the intake of this particular macronutrient through dietary supplements in the form of powders, ready-to-drink shakes, and bars. The primary purpose of protein supplementation is to augment dietary protein intake, aiding individuals in meeting their protein requirements, especially when it may be challenging to do so through regular food (i.e. chicken, beef, fish, pork, etc.) sources alone. A large body of evidence shows that protein has an important role in exercising and sedentary individuals. A PubMed search of "protein and exercise performance" reveals thousands of publications. Despite the considerable volume of evidence, it is somewhat surprising that several persistent questions and misconceptions about protein exist. The following are addressed: 1) Is protein harmful to your kidneys? 2) Does consuming "excess" protein increase fat mass? 3) Can dietary protein have a harmful effect on bone health? 4) Can vegans and vegetarians consume enough protein to support training adaptations? 5) Is cheese or peanut butter a good protein source? 6) Does consuming meat (i.e., animal protein) cause unfavorable health outcomes? 7) Do you need protein if you are not physically active? 8) Do you need to consume protein ≤ 1 hour following resistance training sessions to create an anabolic environment in skeletal muscle? 9) Do endurance athletes need additional protein? 10) Does one need protein supplements to meet the daily requirements of exercise-trained individuals? 11) Is there a limit to how much protein one can consume in a single meal? To address these questions, we have conducted a thorough scientific assessment of the literature concerning protein supplementation.

The Anabolic Response to a Ground Beef Patty and Soy-Based Meat Alternative: A Randomized Controlled Trial

BACKGROUND

Soy-based meat alternatives (SBMA) are becoming increasingly popular, but it is unclear if they have the same anabolic effect on skeletal muscle as animal meat.

OBJECTIVE

We aimed to compare the stimulation of skeletal muscle protein synthesis by consumption of one or two 4 oz patties of SBMA with 4 oz (80%protein/20%fat) beef.

METHODS

The study design was a randomized controlled trial. Participants were aged 18 to 40 years of age and in good general health with a BMI between 20 and 32 kg/m2. Stable isotope tracer methods were used (L-[ring-2H5] phenylalanine, [U-13C9-15N]- tyrosine and L-[ring-2H4] tyrosine) to quantify the response of muscle protein fractional synthetic rate to consumption of a single beef (4 oz), single SBMA (4 oz), or two 4 oz SBMA patties (8 oz). Whole-body rates of protein synthesis, breakdown and net balance, as well as plasma essential amino acid (EAA) concentrations, were also measured.

RESULTS

The increase above basal in muscle protein FSR following consumption of the 4 oz beef patty (0.020 ± 0.016%/hour) was significantly greater than the increase following consumption of 4 oz SBMA (p = 0.021; 0.003 ± 0.010%/hour) but not 8 oz SBMA (p = 0.454; 0.013 ± 0.016%/hour). The maximal EAA concentration was significantly correlated (p = 0.046; r = 0.411) with the change in muscle FSR from the basal to postprandial period. In addition, the change in muscle FSR from the basal to postprandial period was significantly correlated (p = 0.046; r = 0.412) with the corresponding change in whole-body protein synthesis.

CONCLUSION

Consumption of a 4 oz beef patty stimulates muscle and whole -body protein synthesis more than a 4 oz SBMA patty and similarly to 8 oz of SBMA.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT05197140.

Compartmental analysis: a new approach to estimate protein breakdown and meal response in health and critical illness

Purpose of review

This study aimed to discuss the use of the pulse stable isotope tracer approach to study changes in metabolism in healthy individuals and critically ill patients.

Recent findings and conclusion

We found that in the postabsorptive state and healthy condition, intracellular protein breakdown and net intracellular protein breakdown, when calculated using the pulse tracer approach, are about double what has previously been reported using the more traditional primed-constant and continuous stable isotope approaches (600 versus 300 grams of protein/day). In critically ill patients, protein breakdown is even higher and calculated to be approximately 900 grams of protein/day, using the pulse tracer approach. Based on these data, we hypothesize that reducing protein breakdown in the postabsorptive state is key when trying to improve the condition of critically ill patients. Moreover, we also used the pulse tracer approach during feeding to better estimate the intracellular metabolic response to feeding. Our first observation is that endogenous protein breakdown does not seem to be reduced during feeding. We also have shown that when consuming a meal with a certain amount of protein, the biological value of that protein meal can be calculated with the pulse tracer approach. In conclusion, using the pulse stable isotope tracer approach to study protein kinetics in the postabsorptive state and during feeding expands our understanding of how dietary proteins can affect human protein metabolism. The intracellular protein synthesis stimulatory effect of a meal is an important factor to consider when calculating the exact protein requirements and needs, particularly in critical illness.

Collagen peptides supplementation improves function, pain, and physical and mental outcomes in active adults

INTRODUCTION

Chronic pain affects 19% of adults in the United States, with increasing prevalence in active and aging populations. Pain can limit physical activity and activities of daily living (ADLs), resulting in declined mental and social health. Nutritional interventions for pain currently target inflammation or joint health, but few influence both. Collagen, the most abundant protein in the human body and constituent of the extra cellular matrix, is such a nutraceutical. While there have been reports of reductions in pain with short-term collagen peptide (CP) supplementation, there are no long-term studies specifically in healthy middle-aged active adults.

PURPOSE

To determine the effects of daily CP consumption over 3, 6, and 9 months on survey measures of pain, function, and physical and mental health using The Knee Injury & Osteoarthritis Outcomes Score (KOOS) and Veterans Rand 12 (VR-12) in middle-aged active adults.

METHODS

This study was a double-blind randomized control trial with three treatment groups (Placebo, 10 g/d CP, and 20 g/d CP).

RESULTS

Improvements in ADLs (p = .031, ηp2 = .096) and pain (p = .037, ηp2 = .164) were observed with 10 g/d CP over 6 months, although pain only improved in high frequency exercisers (>180 min/week). Additionally, VR-12 mental component scores (MCS) improved with 10 g/d of CP over 3-9 months (p = .017, ηp2 = .309), while physical component scores (PCS) improved with 20 g/d of CP over 3-9 months, but only in females (p = .013, ηp2= .582).

CONCLUSION

These findings suggest 10 to 20 g/d of CP supplementation over 6 to 9 months may improve ADLs, pain, MCS, and PCS in middle-aged active adults.

Dietary protein recommendations to support healthy muscle ageing in the 21st century and beyond: considerations and future directions

This review explores the evolution of dietary protein intake requirements and recommendations, with a focus on skeletal muscle remodelling to support healthy ageing based on presentations at the 2023 Nutrition Society summer conference. In this review, we describe the role of dietary protein for metabolic health and ageing muscle, explain the origins of protein and amino acid (AA) requirements and discuss current recommendations for dietary protein intake, which currently sits at about 0⋅8 g/kg/d. We also critique existing (e.g. nitrogen balance) and contemporary (e.g. indicator AA oxidation) methods to determine protein/AA intake requirements and suggest that existing methods may underestimate requirements, with more contemporary assessments indicating protein recommendations may need to be increased to >1⋅0 g/kg/d. One example of evolution in dietary protein guidance is the transition from protein requirements to recommendations. Hence, we discuss the refinement of protein/AA requirements for skeletal muscle maintenance with advanced age beyond simply the dose (e.g. source, type, quality, timing, pattern, nutrient co-ingestion) and explore the efficacy and sustainability of alternative protein sources beyond animal-based proteins to facilitate skeletal muscle remodelling in older age. We conclude that, whilst a growing body of research has demonstrated that animal-free protein sources can effectively stimulate and support muscle remodelling in a manner that is comparable to animal-based proteins, food systems need to sustainably provide a diversity of both plant and animal source foods, not least for their protein content but other vital nutrients. Finally, we propose some priority research directions for the field of protein nutrition and healthy ageing.

Menopause Transition: A Cross-Sectional Evaluation on Muscle Size and Quality

INTRODUCTION

The menopause transition yields significant physiological alterations. The purpose was to characterize lean soft tissue (LST), muscle size (muscle cross-sectional area (mCSA)), muscle quality (echo intensity (EI)), and strength across the menopause transition. A secondary aim was to evaluate whole-body protein turnover in a subsample of women.

METHODS

Seventy-two healthy women were enrolled in this cross-sectional study based on menopause stage (PRE: n = 24; PERI: n = 24; POST: n = 24). Whole-body LST was measured via dual-energy x-ray absorptiometry, and muscle characteristics (mCSA and EI) were measured via B-mode ultrasound of the vastus lateralis. Maximal voluntary contractions (N·m) of the knee extensors were evaluated. Physical activity (in minutes per day) was accounted for using the International Physical Activity Questionnaire. A subsample of women ( n = 27) ingested 2.0 g of 15 N-alanine to determine whole-body net protein balance (NB; in grams per kilogram of body mass per day).

RESULTS

Significant differences were evident in LST ( P = 0.022), leg LST ( P = 0.05), and EI ( P = 0.018) between menopause stages. Bonferroni post-hoc comparisons revealed greater LST in PRE versus PERI (mean difference (MD) ± SE, 3.8 ± 1.5 kg; P = 0.048) and POST (3.9 ± 1.5 lb; P = 0.049). Similarly, EI was significantly higher in PERI PRE (MD, 18.3 ± 7.1 a.u.; P = 0.036). There was no significant difference in mCSA ( P = 0.082) or in maximal voluntary contraction ( P = 0.167). NB was significantly different across groups ( P = 0.026); NB was greater in PRE compared with PERI (MD, 0.39 ± 0.17 g·kg -1 ; P = 0.090), and from PRE to POST (MD, 0.46 ± 0.17 g·kg -1 ; P = 0.042). Physical activity was not significantly different across groups but demonstrated a linear increase from PRE to POST.

CONCLUSIONS

The current findings suggest that LST, muscle quality, and protein balance may be negatively influenced by the menopause transition.

Measuring muscle protein synthesis in humans and the influence of nutritional state

In 1982 and 2011, Clinical Science published papers that used infusion of stable isotope-labeled amino acids to assess skeletal muscle protein synthesis in the fasted and fed state and before and after a period of increased intake of omega-3 fatty acids, respectively; both of these papers have been highly cited. An overview of the study designs, key findings and novel features, and a consideration of the lasting impact of these two papers is presented.

The earlier paper introduced stable isotope tracer approaches in humans that showed consuming a meal will increase whole body oxidation, synthesis, and breakdown of protein, but that protein synthesis is greater than breakdown resulting in net accumulation of protein. The paper also demonstrated that consuming a meal promotes net protein synthesis in skeletal muscle.

The later paper introduced the concept that omega-3 polyunsaturated fatty acids are able to improve anabolism by reporting that 8 weeks consumption of high-dose omega-3 fatty acids by healthy young and middle-aged adults increased skeletal muscle protein synthesis during a hyperaminoacidemic–hyperinsulinemic clamp compared with what was seen during the clamp at study entry. Omega-3 fatty acids also increased the phosphorylation of important signaling proteins in muscle, including mammalian target of rapamycin, p70s6k, and Akt, during the clamp.

These two papers remain relevant because they offer experimental approaches to study human (patho)physiology in different contexts, they present novel insights into the impact of nutritional state (feeding) and specific nutrients (omega-3 fatty acids) on muscle protein synthesis, and they suggest ways to explore the potential of interventions to help prevent and reverse the age-, disease-, and disuse-associated decline in muscle mass.

Continuous oral stable isotope ingestion to measure whole-body protein turnover

BACKGROUND & AIMS

Protein kinetic responses to nutrition and exercise interventions are commonly evaluated using a primed-constant infusion of stable isotope tracers. While this methodology is state-of-the-art, the required preparation at a certified pharmacy makes the utilization of isotope infusion both expensive and logistically cumbersome. Oral tracer ingestion has been used to quantify 24-h whole-body protein status; however, this does not permit examination of acute interventional effects. Ingestion of a priming bolus, followed by continuous ingestion of stable isotope tracer in a 'sip feeding' fashion may provide a more feasible alternative for quantifying acute kinetic responses. Therefore, the purpose of this study was to evaluate the viability of a primed continuous oral sip-ingestion method of stable isotope tracers for the evaluation of whole-body protein kinetics.

METHODS

In a randomized, crossover design, eight healthy adults (63% female; Age: 29.4 ± 5.8 yrs; BMI: 24.3 ± 2.7 kg/m²) completed two, two-period stable isotope oral ingestion studies, consisting of a 3 h basal fasted period, followed by a 4-h post-ingestion period. After the basal period, subjects ingested either 6.3 g (Low) or 12.6 g (High) of an essential amino acid (EAA) enriched whey protein supplement. The continuous oral sip-feed method was initiated with a primed oral bolus dose of L-[ring-²H₅]phenylalanine, L-[ring-²H₂]tyrosine, and L-[ring-²H₄]tyrosine, followed by oral sip doses of L-[ring-²H₅]phenylalanine, L-[ring-²H₂]tyrosine every 10 min to approximate steady state tracer enrichment. Blood samples were taken throughout the basal and post-meal periods to determine tracer enrichment. Whole-body net protein balance (NB), synthesis (PS), breakdown (PB), and exogenous hydroxylation were calculated for each period. Repeated measure ANOVAs (treatment × time) were used to assess differences in protein kinetics.

RESULTS

Using the sip feed method, NB, PS, and hydroxylation were significantly increased with ingestion of protein (p < 0.05) during the postprandial period, regardless of amount of protein ingested; ΔNB from the postabsorptive to postprandial period was significantly greater for high compared to low protein (p = 0.026; low = 6.2 ± 5.1 g protein·240 min^-1; high = 11.8 ± 3.9 g protein·240 min^-1).

CONCLUSION

The current study provides preliminary evidence that continuous oral sip-feeding of stable isotope tracer is a feasible method that provides physiologically relevant measures of protein metabolism. Assessments of variance and individual responses revealed high measurement variability with the sip-feed method compared to previously published constant infusion responses, but ΔNB, ΔPS, and ΔPB were comparable. In situations where constant infusion is not feasible, oral sip-feeding could be used as an alternative method for measurement of acute, postprandial protein metabolism.

Intestinal dysfunction in chronic disease

PURPOSE OF REVIEW

This review will discuss recent studies showing that patients with chronic wasting diseases suffer from a variety of small intestinal impairments which might negatively impact the colonic microbiota and overall well-being. New insights will be addressed as well as novel approaches to assess intestinal function.

RECENT FINDINGS

Small intestinal dysfunction can enhance the amount and alter the composition of undigested food reaching the colon. As a result of reduced protein digestion and absorption, a large amount of undigested protein might reach the colon promoting the presence of pathogenic colonic bacteria and a switch from bacterial fiber fermentation to protein fermentation. While microbial metabolites of fiber fermentation, such as short-chain fatty acids (SCFA), are mainly considered beneficial for overall health, metabolites of protein fermentation, i.e. ammonia, branched SCFAs, hydrogen sulfide, polyamines, phenols, and indoles, can exert beneficial or deleterious effects on overall health. Substantial advances have been made in the assessment of small intestinal dysfunction in chronic diseases, but studies investigating the connection to colonic microbial metabolism are needed. A promising new stable isotope approach can enable the measurement of metabolite production by the colonic microbiota.

SUMMARY

Several studies have been conducted to assess intestinal function in chronic diseases. Impairments in intestinal barrier function, sugar absorption, protein digestion, and absorption, as well as small intestinal bacterial overgrowth were observed and possibly might negatively impact colonic bacterial metabolism. We suggest that improving these perturbations will improve overall patient health.