There exists a large body of scientific evidence to support protein intakes in excess of the recommended dietary allowance (RDA) (0.8 g protein/kg/day) to promote the retention of skeletal muscle and loss of adipose tissue during dietary energy restriction. Diet-induced weight loss with as low as possible ratio of skeletal muscle to fat mass loss is a situation we refer to as high-quality weight loss. We propose that high-quality weight loss is often of importance to elite athletes in order to maintain their muscle (engine) and shed unwanted fat mass, potentially improving athletic performance. Current recommendations for protein intakes during weight loss in athletes are set at 1.6–2.4 g protein/kg/day. However, the severity of the caloric deficit and type and intensity of training performed by the athlete will influence at what end of this range athletes choose to be. Other considerations regarding protein intake that may help elite athletes achieve weight loss goals include the quality of protein consumed, and the timing and distribution of protein intake throughout the day. This review highlights the scientific evidence used to support protein recommendations for high-quality weight loss and preservation of performance in athletes. Additionally, the current knowledge surrounding the use of protein supplements, branched chain amino acids (BCAA), β-hydroxy β-methylbutyrate (HMB), and other dietary supplements with weight loss claims will be discussed.
Protein Recommendations for Weight Loss in Elite Athletes: A Focus on Body Composition and Performance
Amy J. Hector and Stuart M. Phillips
How Skepticism (not Cynicism) Can Raise Scientific Standards and Reform the Health and Wellness Industry
Nicholas B. Tiller and Stuart M. Phillips
A Critical Examination of Dietary Protein Requirements, Benefits, and Excesses in Athletes
Stuart M. Phillips, Daniel R. Moore, and Jason E. Tang
There is likely no other dietary component that inspires as much debate, insofar as athletes are concerned, as protein. How much dietary protein is required, optimal, or excessive? Dietary guidelines from a variety of sources have settled on an adequate dietary protein intake for those over the age of 19 of ~0.8–0.9 g protein·kg body weight−1·d−1. According to U.S. and Canadian dietary reference intakes (33), the recommended allowance for protein of 0.8 g protein·kg−1·d−1 is “the average daily intake level that is sufficient to meet the nutrient requirement of nearly all [~98%] . . . healthy individuals” (p. 22). The panel also stated, “in view of the lack of compelling evidence to the contrary, no additional dietary protein is suggested for healthy adults undertaking resistance or endurance exercise” (33, p. 661). Currently, no group or groups of scientists involved in establishing dietary guidelines see a need for any statement that athletes or people engaging in regular physical activity require more protein than their sedentary counterparts. Popular magazines, numerous Web sites, trainers, and many athletes decry protein intakes even close to those recommended. Even joint position stands from policy-setting groups state that “protein recommendations for endurance athletes are 1.2 to 1.4 g/kg body weight per day, whereas those for resistance and strength-trained athletes may be as high as 1.6 to 1.7 g/kg body weight per day” (1, p. 1544). The divide between those setting dietary protein requirements and those who might be making practical recommendations for athletes appears substantial, but ultimately, most athletes indicate that they consume protein at levels beyond even the highest recommendations. Thus, one might conclude that any debate on protein “requirements” for athletes is inconsequential; however, a critical analysis of existing and new data reveals novel ideas and concepts that may represent some common ground between these apparently conflicted groups. The goal of this review was to provide a critical and thorough analysis of current data on protein requirements in an attempt to provide some guidance to athletes, trainers, coaches, and sport dietitians on athletes’ protein intake. In addition, an effort was made to clearly distinguish between “required” dietary protein, “optimal” intakes, and intakes that are likely “excessive,” perhaps not from the standpoint of health, but certainly from the standpoint of potentially compromised performance.
Dietary Protein for Training Adaptation and Body Composition Manipulation in Track and Field Athletes
Oliver C. Witard, Ina Garthe, and Stuart M. Phillips
Track and field athletes engage in vigorous training that places stress on physiological systems requiring nutritional support for optimal recovery. Of paramount importance when optimizing recovery nutrition are rehydration and refueling which are covered in other papers in this volume. Here, we highlight the benefits for dietary protein intake over and above requirements set out in various countries at ∼0.8–1.0 g·kg body mass (BM)−1·day−1 for training adaptation, manipulating body composition, and optimizing performance in track and field athletes. To facilitate the remodeling of protein-containing structures, which are turning over rapidly due to their training volumes, track and field athletes with the goal of weight maintenance or weight gain should aim for protein intakes of ∼1.6 g·kg BM−1·day−1. Protein intakes at this level would not necessarily require an overemphasis on protein-containing foods and, beyond convenience, does not suggest a need to use protein or amino acid-based supplements. This review also highlights that optimal protein intakes may exceed 1.6 g·kg BM−1·day−1 for athletes who are restricting energy intake and attempting to minimize loss of lean BM. We discuss the underpinning rationale for weight loss in track and field athletes, explaining changes in metabolic pathways that occur in response to energy restriction when manipulating protein intake and training. Finally, this review offers practical advice on protein intakes that warrant consideration in allowing an optimal adaptive response for track and field athletes seeking to train effectively and to lose fat mass while energy restricted with minimal (or no) loss of lean BM.
Celebrating the Professional Life of Professor Kevin D. Tipton (1961–2022)
Oliver C. Witard, Arny A. Ferrando, and Stuart M. Phillips
This invited editorial celebrates the distinguished professional life of Professor Kevin D. Tipton, who sadly passed away on January 9, 2022. Professor Tipton made an outstanding contribution to the scientific field of sport nutrition and exercise metabolism over an exceptional 30-year career. He dedicated his academic career to understanding the response of muscle protein metabolism to exercise and nutrition. The impact of his work is far-reaching with application to athletes in terms of promoting training adaptation, recovery, and performance, alongside clinical implications for injury management and healthy aging. Notable scientific contributions included the first in vivo human study to demonstrate the role of orally ingested essential amino acids in stimulating muscle protein synthesis during acute post-exercise recovery. This finding laid the foundation for future studies to interrogate the response of muscle protein synthesis to the ingestion of different protein types. Professor Tipton’s work also included investigating the maximally effective dose and timing (regarding exercise) of ingested protein for the stimulation of muscle protein synthesis. Kevin will be remembered fondly by academics, applied scientists, and students across the sport nutrition and exercise metabolism community as a leading researcher in the field, a critical thinker, and an inspirational teacher. His mission was to educate the next generation of exercise scientists by sharing his distinct wealth of knowledge accrued over three decades. Above all else, Kevin was kind, generous (with his time and knowledge), honest, and incredibly social. He was a unique character and will be greatly missed among our community but certainly never forgotten.
The Reliability of 4-Minute and 20-Minute Time Trials and Their Relationships to Functional Threshold Power in Trained Cyclists
Martin J. MacInnis, Aaron C.Q. Thomas, and Stuart M. Phillips
Purpose: The mean power output (MPO) from a 60-min time trial (TT)—also known as functional threshold power, or FTP—is a standard measure of cycling performance; however, shorter performance tests are desirable to reduce the burden of performance testing. The authors sought to determine the reliability of 4- and 20-min TTs and the extent to which these short TTs were associated with 60-min MPO. Methods: Trained male cyclists (n = 8; age = 25  y; = 71  mL/kg/min) performed two 4-min TTs, two 20-min TTs, and one 60-min TT. Critical power (CP) was estimated from 4- and 20-min TTs. The typical error of the mean (TEM) and intraclass correlation coefficient (ICC) were calculated to assess reliability, and R 2 values were calculated to assess relationships with 60-min MPO. Results: Pairs of 4-min TTs (mean: 417 [SD: 45] W vs 412  W, P = .25; TEM = 8.1 W; ICC = .98), 20-min TTs (342  W vs 344  W, P = .41; TEM = 4.6 W; ICC = .99), and CP estimates (323  W vs 328  W, P = .25; TEM = 6.5; ICC = .98) were reliable. The 4-min MPO (R 2 = .95), 20-min MPO (R 2 = .92), estimated CP (R 2 = .82), and combination of the 4- and 20-min MPO (adjusted R 2 = .98) were strongly associated with the 60-min MPO (309  W). Conclusion: The 4- and 20-min TTs appear useful for assessing performance in trained, if not elite, cyclists.
Postexercise Dietary Protein Strategies to Maximize Skeletal Muscle Repair and Remodeling in Masters Endurance Athletes: A Review
Thomas M. Doering, Peter R. Reaburn, Stuart M. Phillips, and David G. Jenkins
Participation rates of masters athletes in endurance events such as long-distance triathlon and running continue to increase. Given the physical and metabolic demands of endurance training, recovery practices influence the quality of successive training sessions and, consequently, adaptations to training. Research has suggested that, after muscle-damaging endurance exercise, masters athletes experience slower recovery rates in comparison with younger, similarly trained athletes. Given that these discrepancies in recovery rates are not observed after non–muscle-damaging exercise, it is suggested that masters athletes have impairments of the protein remodeling mechanisms within skeletal muscle. The importance of postexercise protein feeding for endurance athletes is increasingly being acknowledged, and its role in creating a positive net muscle protein balance postexercise is well known. The potential benefits of postexercise protein feeding include elevating muscle protein synthesis and satellite cell activity for muscle repair and remodeling, as well as facilitating muscle glycogen resynthesis. Despite extensive investigation into age-related anabolic resistance in sedentary aging populations, little is known about how anabolic resistance affects postexercise muscle protein synthesis and thus muscle remodeling in aging athletes. Despite evidence suggesting that physical training can attenuate but not eliminate age-related anabolic resistance, masters athletes are currently recommended to consume the same postexercise dietary protein dose (approximately 20 g or 0.25 g/kg/meal) as younger athletes. Given the slower recovery rates of masters athletes after muscle-damaging exercise, which may be due to impaired muscle remodeling mechanisms, masters athletes may benefit from higher doses of postexercise dietary protein, with particular attention directed to the leucine content of the postexercise bolus.
Self–Myofascial Release: No Improvement of Functional Outcomes in “Tight” Hamstrings
Robert W. Morton, Sara Y. Oikawa, Stuart M. Phillips, Michaela C. Devries, and Cameron J. Mitchell
Self–myofascial release (SMR) is a common exercise and therapeutic modality shown to induce acute improvements in joint range of motion (ROM) and recovery; however, no long-term studies have been conducted. Static stretching (SS) is the most common method used to increase joint ROM and decrease muscle stiffness. It was hypothesized that SMR paired with SS (SMR+SS) compared with SS alone over a 4-wk intervention would yield greater improvement in knee-extension ROM and hamstring stiffness.
19 men (22 ± 3 y) with bilateral reduced hamstring ROM had each of their legs randomly assigned to either an SMR+SS or an SS-only group. The intervention consisted of 4 repetitions of SS each for 45 s or the identical amount of SS preceded by 4 repetitions of SMR each for 60 s and was performed on the respective leg twice daily for 4 wk. Passive ROM, hamstring stiffness, rate of torque development (RTD), and maximum voluntary contraction (MVC) were assessed pre- and postintervention.
Passive ROM (P < .001), RTD, and MVC (P < .05) all increased after the intervention. Hamstring stiffness toward end-ROM was reduced postintervention (P = .02). There were no differences between the intervention groups for any variable.
The addition of SMR to SS did not enhance the efficacy of SS alone. SS increases joint ROM through a combination of decreased muscle stiffness and increased stretch tolerance.
Presleep α-Lactalbumin Consumption Does Not Improve Sleep Quality or Time-Trial Performance in Cyclists
Martin J. MacInnis, Christine E. Dziedzic, Emily Wood, Sara Y. Oikawa, and Stuart M. Phillips
We tested the hypothesis that presleep consumption of α-lactalbumin (LA), a fraction of whey with a high abundance of tryptophan, would improve indices of sleep quality and time-trial (TT) performance in cyclists relative to an isonitrogenous collagen peptide (CP) supplement lacking tryptophan. Using randomized, double-blind, crossover designs, cyclists consumed either 40 g of LA or CP 2 hr prior to sleep. In Study 1, six elite male endurance track cyclists (age 23 ± 6 years,
Whey Protein Supplementation Is Superior to Leucine-Matched Collagen Peptides to Increase Muscle Thickness During a 10-Week Resistance Training Program in Untrained Young Adults
Jeferson L. Jacinto, João P. Nunes, Stefan H.M. Gorissen, Danila M.G. Capel, Andrea G. Bernardes, Alex S. Ribeiro, Edilson S. Cyrino, Stuart M. Phillips, and Andreo F. Aguiar
The purpose of this study was to investigate the effects of supplementation of whey protein (WP) versus leucine-matched collagen peptides (CP) on muscle thickness MT and performance after a resistance training (RT) program in young adults. Twenty-two healthy untrained participants were randomly assigned to either a WP (n = 11) or leucine-matched CP (n = 11) group and then submitted to a supervised 10-week RT program (3 days/week). The groups were supplemented with an equivalent amount of WP (35 g, containing 3.0 g of leucine) and CP (35 g, containing 1.0 g of leucine and 2.0 g of free leucine) during the intervention period (after each workout and in the evening on nontraining days). MT of the vastus lateralis and biceps brachii, isokinetic peak torque and mean power output of the elbow flexors, and peak power output of the lower body were assessed before and after the RT program. The WP group experienced a greater (interaction, p < .05) increase in the vastus lateralis (effect size, WP = 0.68 vs. CP = 0.38; % Δ, WP = 8.4 ± 2.5 vs. CP = 5.6 ± 2.6%) and biceps brachii muscle thickness (effect size, WP = 0.61 vs. CP = 0.35; % , WP = 10.1 ± 3.8 vs. CP = 6.0 ± 3.2%), with a similar increase in muscle performance (peak torque, mean power output, and peak power output) between groups (time p < .05). Supplementation with WP was superior to leucine content-matched CP supplementation in increasing muscle size, but not strength and power, after a 10-week RT program in young adults.