Considerations for a protein-focused screening instrument in clinical nutrition assessment.

Physiological stress during injury and surgery negatively impacts protein balance and muscle mass maintenance. Adequate perioperative protein intake may attenuate muscle atrophy to maintain and facilitate functional recovery, particularly in older adults; yet, screening tools routinely used in clinical settings do not specifically assess protein intake when assessing nutrition risk. Although assessing malnutrition is a priority, suboptimal protein intake in non-malnourished patients should also be identified given protein's critical role in muscle health. This opinion paper highlights the potential for using a clinically appropriate protein-focused screener for rapid and efficient characterization of protein intake.

Exercise and Protein Supplementation Recommendations for Older Adults With Sarcopenic Obesity: A Meta-Review.

This systematic meta-review evaluated the effects of exercise with and without protein interventions on muscle strength and function in older adults with sarcopenic obesity. PubMed, Cochrane Database of Systematic Reviews, Cumulative Index to Nursing and Allied Health Literature, Scopus, and SPORTDiscus databases were searched through February 2021 for relevant systematic reviews and meta-analyses with aerobic, resistance, and/or combined training interventions with and without protein supplementation in older adults ≥ 65 years with sarcopenic obesity. This meta-review showed that exercise with and without protein supplementation improved body composition (i.e., decreased percentage body fat) and functional outcomes (i.e., gait speed and grip strength). Because the current literature is limited, determining the effects of exercise and combined protein supplementation in this population requires further investigation. In the meantime, protein recommendations should align with general sarcopenia recommendations. Based upon available findings, tentative exercise recommendations to optimize health outcomes in this population are proposed.

Fruit juice and childhood obesity: a review of epidemiologic studies.

Childhood obesity is a national epidemic, and many efforts have been made to understand its risk factors. The purpose of this review was to provide an updated account of the observational studies evaluating the relationship between 100% fruit juice intake and obesity in children and adolescents, and to highlight the major risk factors that may impact this relationship. PubMed and Scopus were searched for terms related to fruit juice and childhood obesity, and studies assessing 100% fruit juice intake in participants ≤ 19 years old, with obesity-related outcomes (BMI or adiposity), and published before March 9, 2021 were included. There were 17 prospective cohort and 14 cross-sectional studies included in the analysis. Overall, the evidence does not support a relationship between 100% fruit juice intake and measures of obesity in most children. There is some evidence to suggest a minor positive association in some overweight or very young children, but due to fundamental differences and limitations in methodology, further investigation is required. Significant gaps in literature on this topic exist particularly in regards to randomized clinical trials in children, and in studies in racially diverse populations.

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

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

Exercise/Physical Activity in Individuals with Type 2 Diabetes: A Consensus Statement from the American College of Sports Medicine.

ABSTRACT: This consensus statement is an update of the 2010 American College of Sports Medicine position stand on exercise and type 2 diabetes. Since then, a substantial amount of research on select topics in exercise in individuals of various ages with type 2 diabetes has been published while diabetes prevalence has continued to expand worldwide. This consensus statement provides a brief summary of the current evidence and extends and updates the prior recommendations. The document has been expanded to include physical activity, a broader, more comprehensive definition of human movement than planned exercise, and reducing sedentary time. Various types of physical activity enhance health and glycemic management in people with type 2 diabetes, including flexibility and balance exercise, and the importance of each recommended type or mode are discussed. In general, the 2018 Physical Activity Guidelines for Americans apply to all individuals with type 2 diabetes, with a few exceptions and modifications. People with type 2 diabetes should engage in physical activity regularly and be encouraged to reduce sedentary time and break up sitting time with frequent activity breaks. Any activities undertaken with acute and chronic health complications related to diabetes may require accommodations to ensure safe and effective participation. Other topics addressed are exercise timing to maximize its glucose-lowering effects and barriers to and inequities in physical activity adoption and maintenance.

Physiological Limitations of Protein Foods Ounce Equivalents and the Underappreciated Role of Essential Amino Acid Density in Healthy Dietary Patterns.

Protein quality is an important component of protein intake to support growth, development, and maintenance of essential body tissues and functions. Therefore, protein quality should be emphasized as a key characteristic during protein food selection within the larger context of healthy dietary patterns, especially when considering the wide variance of protein quality across animal- and plant-based foods. However, the USDA Dietary Guidelines for Americans (DGA) do not address specific protein quality recommendations within their protein foods ounce equivalents guidance or as a component of Healthy U.S. Style, Healthy Vegetarian, and Healthy Mediterranean Style dietary patterns. In addition, the protein foods ounce equivalents within the DGA are not established on any obvious metabolic equivalency characteristic [i.e., energy, protein, or essential amino acid (EAA) content], which creates misleading messaging of equivalent functional and metabolic benefit across protein foods. EAA content is a key characteristic of protein quality and can be a practical focal point for protein intake recommendations and achieving healthy dietary patterns. This review discusses the importance of protein quality, the state of messaging within DGA recommendations, and proposes EAA density (i.e., EAA content relative to total energy) as one practical approach to improve current dietary recommendations. Two recent publications that evaluated the DGA protein foods ounce equivalents based on metabolic effect and their application within DGA recommended dietary patterns are discussed.

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.

Divergent Roles of Inflammation in Skeletal Muscle Recovery From Injury.

A transient increase in local pro-inflammatory cytokine expression following skeletal muscle injury mediates the repair and regeneration of damaged myofibers through myogenesis. Regenerative capacity is diminished and muscle wasting occurs, however, when intramuscular inflammatory signaling is exceedingly high or persists chronically. An excessive and persistent inflammatory response to muscle injury may therefore impair recovery by limiting the repair of damaged tissue and triggering muscle atrophy. The concentration-dependent activation of different downstream signaling pathways by several pro-inflammatory cytokines in cell and animal models support these opposing roles of post-injury inflammation. Understanding these molecular pathways is essential in developing therapeutic strategies to attenuate excessive inflammation and accelerate functional recovery and muscle mass accretion following muscle damage. This is especially relevant given the observation that basal levels of intramuscular inflammation and the inflammatory response to muscle damage are not uniform across all populations, suggesting certain individuals may be more susceptible to an excessive inflammatory response to injury that limits recovery. This narrative review explores the opposing roles of intramuscular inflammation in muscle regeneration and muscle protein turnover. Factors contributing to an exceedingly high inflammatory response to damage and age-related impairments in regenerative capacity are also considered.

Skeletal Muscle Disuse Atrophy and the Rehabilitative Role of Protein in Recovery from Musculoskeletal Injury.

Muscle atrophy and weakness occur as a consequence of disuse after musculoskeletal injury (MSI). The slow recovery and persistence of these deficits even after physical rehabilitation efforts indicate that interventions designed to attenuate muscle atrophy and protect muscle function are necessary to accelerate and optimize recovery from MSI. Evidence suggests that manipulating protein intake via dietary protein or free amino acid-based supplementation diminishes muscle atrophy and/or preserves muscle function in experimental models of disuse (i.e., immobilization and bed rest in healthy populations). However, this concept has rarely been considered in the context of disuse following MSI, which often occurs with some muscle activation during postinjury physical rehabilitation. Given that exercise sensitizes skeletal muscle to the anabolic effect of protein ingestion, early rehabilitation may act synergistically with dietary protein to protect muscle mass and function during postinjury disuse conditions. This narrative review explores mechanisms of skeletal muscle disuse atrophy and recent advances delineating the role of protein intake as a potential countermeasure. The possible synergistic effect of protein-based interventions and postinjury rehabilitation in attenuating muscle atrophy and weakness following MSI is also considered.

Effective translation of current dietary guidance: understanding and communicating the concepts of minimal and optimal levels of dietary protein.

Dietitians and health care providers have critical roles in the translation of the dietary guidance to practice. The protein content of diets for adults can be based on the Recommended Dietary Allowance (RDA) of 0.80 g/kg per day. Alternatively, the most recent Dietary Reference Intakes (DRIs) for macronutrients reflect expanded guidance for assessing protein needs and consider the relative relation of absolute amounts of protein, carbohydrate, and fat to total energy intake in the context of chronic disease prevention. The Acceptable Macronutrient Distribution Range (AMDR) reflects the interrelation between the macronutrients and affords dietitians and clinicians additional flexibility in diet planning. Accounting for the caloric value of RDAs for carbohydrate and fat, "flexible calories" emerge as an opportunity to create varied eating plans that provide for protein intakes in excess of the RDA but within the AMDR. Protein Summit 2.0 highlighted the growing body of scientific evidence documenting the benefits of higher protein intakes at amounts approximating twice the RDA, which include promotion of healthy body weight and preservation of lean body mass and functional ability with age. The essential amino acid (EAA) density of a food also emerged as a novel concept analogous to "nutrient density," which can enable the practitioner to calculate the caloric cost associated with a specific protein source to attain the daily requirement of EAAs to accomplish various health outcomes because these indispensable nutrients have a significant role in protein utilization and metabolic regulation. Tailoring recommendations unique to an individual's varying goals and needs remains a challenge. However, flexibility within the application of DRIs to include consideration of the AMDR provides a sound framework to guide practitioners in effective translation of current dietary guidance with a specific regard for the documented benefits of higher protein intakes.

Protein and healthy aging.

Our understanding of the potential benefits and challenges of optimizing dietary protein intake in older adults continues to evolve. An overarching hypothesis generated during Protein Summit 2.0 was that consuming an adequate amount of high-quality protein at each meal, in combination with physical activity, may delay the onset of sarcopenia, slow its progression, reduce the magnitude of its functional consequences, or all of these. The potential benefits of young and middle-aged adults adopting a diet pattern whereby adequate protein is consumed at each meal as a countermeasure to sarcopenia are presented and discussed. For example, meeting a protein threshold (∼25-30 g/meal) represents a promising, yet still largely unexplored dietary strategy to help maintain muscle mass and function. For many older adults, breakfast is a carbohydrate-dominated lower-protein meal and represents an opportunity to improve and more evenly distribute daily protein intake. Although both animal and plant-based proteins can provide the required essential amino acids for health, animal proteins generally have a higher proportion of the amino acid leucine. Leucine plays a key role in stimulating translation initiation and muscle protein anabolism and is the focus of ongoing research. Protein requirements should be assessed in the light of habitual physical activity. An evenly distributed protein diet provides a framework that allows older adults to benefit from the synergistic anabolic effect of protein and physical activity. To fully understand the role of dietary protein intake in healthy aging, greater efforts are needed to coordinate and integrate research design and data acquisition and interpretation from a variety of disciplines.

Hydration Status and Sodium Balance of Endurance Runners Consuming Postexercise Supplements of Varying Nutrient Content.

Postexercise protein and sodium supplementation may aid recovery and rehydration. Preserved beef provides protein and contains high quantities of sodium that may alter performance related variables in runners. The purpose of this study was to determine the effects of consuming a commercial beef product postexercise on sodium and water balance. A secondary objective was to characterize effects of the supplementation protocols on hydration, blood pressure, body mass, and running economy. Eight trained males (age = 22 ± 3 y, VO2max = 66.4 ± 4.2 ml·kg-1·min-1) completed three identical weeks of run training (6 run·wk-1, 45 ± 6 min·run-1, 74 ± 5% HRR). After exercise, subjects consumed either, a beef nutritional supplement (beef jerky; [B]), a standard recovery drink (SRD), or SRD+B in a randomized counterbalanced design. Hydration status was assessed via urinary biomarkers and body mass. No main effects of treatment were observed for 24 hr urine volume (SRD, 1.7 ± 0.5; B, 1.8 ± 0.6; SRD+B, 1.4 ± 0.4 L·d-1), urine specific gravity (1.016 ± 0.005, 1.018 ± 0.006, 1.017 ± 0.006) or body mass (68.4 ± 8.2, 68.3 ± 7.7, 68.2 ± 8.1 kg). No main effect of treatment existed for sodium intake-loss (-713 ± 1486; -973 ± 1123; -980 ± 1220 mg·d-1). Mean arterial pressure (81.0 ± 4.6, 81.1 ± 7.3, 83.8 ± 5.4 mm Hg) and average exercise running economy (VO2: SRD, 47.9 ± 3.2; B, 47.2 ± 2.6; SRD+B, 46.2 ± 3.4 ml·kg-1·min-1) was not affected. Urinary sodium excretion accounted for the daily sodium intake due to the beef nutritional supplement. Findings suggest the commercial beef snack is a viable recovery supplement following endurance exercise without concern for hydration status, performance decrements, or cardiovascular consequences.

Effects of short-term energy deficit on muscle protein breakdown and intramuscular proteolysis in normal-weight young adults.

The effects of short-term energy deficit (ED) on direct measures of muscle proteolysis and the intracellular mechanisms by which muscle proteins are degraded at rest and following aerobic exercise are not well described. This study evaluated the effects of a short-term diet-induced ED, on muscle fractional breakdown rate (FBR), intramuscular 26S proteasome activity, caspase-3 activation, and PSMA2 and MAFbx expression at rest, in the postabsorptive state, and following a single bout of moderate aerobic exercise (45 min at 65% peak oxygen uptake). Six men and 4 women participated in two 10-day diet interventions: weight maintenance (WM) followed by ED (80% estimated energy requirements). Dietary protein (1.5 g·kg(-1)·day(-1)) intake was constant for WM and ED. Mixed muscle FBR, proteasome activity, and intracellular proteolytic factor expression were measured using stable isotope methodology, fluorescent enzyme activity assays, and Western blotting, respectively. Overall, FBR and caspase-3 activation increased 60% and 11%, respectively, in response to ED (P < 0.05), but were not influenced by exercise. During ED, 26S proteasome α-subunit PSMA2 expression was 25% higher (P < 0.05) after exercise compared with rest. Exercise did not influence PSMA2 expression during WM, and MAFbx expression and 26S proteasome activity were not affected by ED or exercise. These data illustrate the effects of short-term, moderate ED on muscle protein degradation. In the context of skeletal muscle integrity during weight loss interventions, this work demonstrates a need for further investigations aimed at mitigating muscle loss associated with energy deficit imposed for intentional reduction of total body weight.

Training table to the battlefield: protein recommendations for warfighters.

Warfighters represent a population of athletes for whom routine training and physical expectations for military operations parallel, and very often exceed, those of their civilian counterparts. Like athletes, warfighters require nutrition support to optimize physical condition to maintain training, sustain performance, speed recovery, and prevent injury and illness. Specifically, energy and protein requirements have been tailored for these populations. Like athletes, warfighters consider protein a critical component of their diet and often incorporate protein supplements into daily diet plans. This article highlights sports nutrition principles that target energy and protein needs of athletes, considers the basis of these recommendations in the context of protein supplementation, and asserts that translating these recommendations to the warfighter is appropriate and necessary. The recommended range of protein intake of 1.2-1.8 g · kg (- 1) · d (- 1) can be extended to the warfighter. Because energy balance is pivotal to optimal protein utilization, adequate energy intake or lack thereof such that a state of negative energy balance exists, should be given particular consideration for the warfighter. Routine protein supplementation is recommended to reduce protein breakdown, support protein synthesis, and promote a positive net protein balance throughout various deployment situations and when energy intake is insufficient.

Chocolate milk and endurance exercise recovery: protein balance, glycogen, and performance.

PURPOSE: This study examined effects of fat-free chocolate milk (MILK) consumption on kinetic and cellular markers of protein turnover, muscle glycogen, and performance during recovery from endurance exercise. METHODS: Male runners participated in two trials separated by 1 wk and consumed either MILK or a nonnitrogenous isocaloric carbohydrate (CHO) control beverage (CON) after a 45-min run at 65% of V˙O(2peak). Postexercise muscle protein fractional synthetic rate (FSR) and whole-body protein turnover were determined during 3 h of recovery using muscle biopsies and primed constant infusions of L-[ring-²H5]phenylalanine and L-[1-¹³C]leucine, respectively. Phosphorylation of translational signaling proteins and activity of proteolytic molecules were determined using Western blotting and enzymatic activity assays. Muscle glycogen was quantified, and treadmill time to exhaustion was determined after the recovery period. RESULTS: Consuming MILK after exercise resulted in higher mixed muscle FSR with lower whole-body proteolysis and synthesis compared with CON (P ≤ 0.05). Phosphorylation of eIF4E-BP1 and FOXO3a was higher for MILK (P < 0.01), whereas Akt phosphorylation was lower during recovery regardless of dietary treatment (P < 0.05). Enzymatic activity assays indicated lower caspase-3 activity during recovery for MILK (P < 0.01) and higher 26S proteasome activity for CON (P < 0.01). Muscle glycogen was not affected by either dietary treatment; however, time to exhaustion was greater for MILK than for CON (P < 0.05). CONCLUSIONS: The effects of consumption of MILK after endurance exercise on FSR, signaling molecules of skeletal muscle protein turnover, leucine kinetics, and performance measures suggest unique benefits of milk compared with a CHO-only beverage.

Assessment of nutrient adequacy with supplement use in a sample of healthy college students.

OBJECTIVES: Limited information is available on the nutritional status and the impact of supplements on nutrient adequacy in college students. This study aimed to assess nutritional status and evaluate the contribution of supplement use to overall nutrient adequacy in a sample of healthy college students. METHODS: Sixty subjects (40 women and 20 men) were randomly recruited from those attending the University of Connecticut. Food records were collected over 30 consecutive days for each subject. In addition, health and lifestyle information was collected at the beginning and end of the study period. RESULTS: After excluding misreporting, only 44 subjects were eligible for assessing nutritional status. More than 40% of female students had intakes below the estimated average requirements for vitamins D and E, calcium, and magnesium. Supplement users had significantly higher average intakes than nonusers from dietary sources for protein, folate, niacin, vitamin E, magnesium, and zinc (p < 0.05). With the addition of supplements, supplement users consumed significantly more for all nutrient intakes except vitamin A than nonusers (p < 0.05). Nutritional adequacy of supplement users was significantly higher for vitamins D and E and magnesium compared with nonusers (p < 0.05). CONCLUSIONS: Overall, men and women were consuming intakes below adequacy for most nutrients, and supplement usage increased nutrient intake and adequacy levels in this young adult population.

Level of dietary protein intake affects glucose turnover in endurance-trained men.

BACKGROUND: To examine the effects of higher-protein diets on endogenous glucose metabolism in healthy, physically active adults, glucose turnover was assessed in five endurance-trained men (age 21.3 ± 0.3 y, VO2peak 70.6 ± 0.1 mL kg-1 min-1) who consumed dietary protein intakes spanning the current dietary reference intakes. FINDINGS: Using a randomized, crossover design, volunteers consumed 4 week eucaloric diets providing either a low (0.8 g kg-1 d-1; LP), moderate (1.8 g kg-1 d-1; MP), or high (3.6 g kg-1 d-1; HP) level of dietary protein. Glucose turnover (Ra, glucose rate of appearance; and Rd glucose rate of disappearance) was assessed under fasted, resting conditions using primed, constant infusions of [6,6-2H2] glucose. Glucose Ra and Rd (mg kg-1 min-1) were higher for MP (2.8 ± 0.1 and 2.7 ± 0.1) compared to HP (2.4 ± 0.1 and 2.3 ± 0.2, P < 0.05) and LP (2.3 ± 0.1 and 2.2 ± 0.1, P < 0.01) diets. Glucose levels (mmol/L) were not different (P > 0.05) between LP (4.6 ± 0.1), MP (4.8 ± 0.1), and HP (4.7 ± 0.1) diets. CONCLUSIONS: Level of protein consumption influenced resting glucose turnover in endurance athletes in a state of energy balance with a higher rate of turnover noted for a protein intake of 1.8 g kg-1 d-1. Findings suggest that consumption of protein in excess of the recommended dietary allowance but within the current acceptable macronutrient distribution range may contribute to the regulation of blood glucose when carbohydrate intake is reduced by serving as a gluconeogenic substrate in endurance-trained men.

Whole body protein kinetics measured with a non-invasive method in severely burned children.

UNLABELLED: Persistent and extensive skeletal muscle catabolism is characteristic of severe burns. Whole body protein metabolism, an important component of this process, has not been measured in burned children during the long-term convalescent period. The aim of this study was to measure whole body protein turnover in burned children at discharge (95% healed) and in healthy controls by a non-invasive stable isotope method. Nine burned children (7 boys, 2 girls; 54±14 (S.D.)% total body area burned; 13±4 years; 45±20 kg; 154±14 cm) and 12 healthy children (8 boys, 4 girls; 12±3 years; 54±16 kg; 150±22 cm) were studied. A single oral dose of (15)N-alanine (16 mg/kg) was given, and thereafter urine was collected for 34 h. Whole body protein flux was calculated from labeling of urinary urea nitrogen. Then, protein synthesis was calculated as protein flux minus excretion, and protein breakdown as flux minus intake. At discharge, total protein turnover was 4.53±0.65 (S.E.)g kg body weight(-1) day(-1) in the burned children compared to 3.20±0.22 g kg(-1) day(-1) in controls (P=0.02). Expressed relative to lean body mass (LBM), the rates were 6.12±0.94 vs. 4.60±0.36 g kg LBM(-1) day(-1) in burn vs. healthy (P=0.06). Total protein synthesis was also elevated in burned vs. healthy children, and a tendency for elevated protein breakdown was observed. CONCLUSION: Total protein turnover is elevated in burned children at discharge compared to age-matched controls, possibly reflecting the continued stress response to severe burn. The oral (15)N-alanine bolus method is a convenient, non-invasive, and no-risk method for measurement of total body protein turnover.