Nutrition
Position Stand
2017
International Society of Sports Nutrition Position Stand: protein and exercise
By Ralf Jager, Chad M. Kerksick, Bill I. Campbell, Paul J. Cribb, Shawn D. Wells, Tim M. Skwiat, Martin Purpura, Tim N. Ziegenfuss, Arny A. Ferrando, Shawn M. Arent, Abbie E. Smith-Ryan, Jeffrey R. Stout, Paul J. Arciero, Michael J. Ormsbee, Lem W. Taylor, Colin D. Wilborn, Doug S. Kalman, Richard B. Kreider, Darryn S. Willoughby, Jay R. Hoffman, Jose L. Krzykowski and Jose Antonio
Journal of the International Society of Sports Nutrition, 14, pp. 20
<h2>Abstract</h2>
<p>This position stand by the International Society of Sports Nutrition (ISSN) provides a comprehensive, evidence-based summary of the relationship between dietary protein intake and exercise performance, with specific recommendations for exercising individuals. Following a <a href="/terms/systematic-review/" class="term-link" data-slug="systematic-review" title="systematic review">systematic review</a> of the available literature, the ISSN expert panel reached the following primary conclusions: exercising individuals require protein intakes substantially above the population RDA, with 1.4-2.0 g/kg/day representing an evidence-supported minimum range; to maximize <a href="/terms/muscle-protein-synthesis/" class="term-link" data-slug="muscle-protein-synthesis" title="muscle protein synthesis">muscle protein synthesis</a> and <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="hypertrophy">hypertrophy</a>, protein intake of 1.6-3.1 g/kg/day may be beneficial depending on training status and energy balance; protein should be distributed evenly across 3-4 meals at approximately 0.25-0.40 g/kg per meal to maximize the anabolic efficiency of daily protein intake; <a href="/terms/protein-timing/" class="term-link" data-slug="protein-timing" title="protein timing">protein timing</a> relative to resistance exercise influences anabolic responses, with the peri-exercise window representing an opportunity for enhanced protein utilization; <a href="/terms/casein/" class="term-link" data-slug="casein" title="casein">casein</a> protein consumed before sleep (30-40 g) enhances overnight muscle protein synthesis; and all protein sources — animal and plant-derived — can support muscle anabolism when total daily intake and <a href="/terms/leucine/" class="term-link" data-slug="leucine" title="leucine">leucine</a> content are adequate. This position stand provides actionable, evidence-graded recommendations for athletes, coaches, and sports nutrition practitioners [1].</p>
<h2>Introduction</h2>
<p>Protein is the most extensively researched macronutrient in the context of exercise and sport, and it is among the most commercially active categories in the sports supplement industry. Despite — or perhaps because of — this high level of interest, the evidence base surrounding dietary protein and exercise has expanded dramatically over the past two decades, producing increasingly refined and nuanced recommendations that supersede earlier, simpler guidance. The International Society of Sports Nutrition (ISSN) periodically reviews this evidence base and issues position stands to provide practitioners and athletes with systematically derived, critically evaluated guidance on topics of central importance to sports nutrition practice [1].</p>
<p>Protein's role in exercise nutrition encompasses multiple biological functions: as the structural raw material for muscle tissue repair and growth; as enzymes mediating metabolic processes; as hormones and signaling molecules; and as a contributor to energy metabolism during prolonged exercise when carbohydrate availability is diminished. For athletes and recreational exercisers, the primary nutritional interest lies in optimizing dietary protein to maximize the adaptive responses to training — particularly the repair and growth of skeletal muscle following resistance exercise and the mitochondrial and <a href="/terms/connective-tissue/" class="term-link" data-slug="connective-tissue" title="connective tissue">connective tissue</a> remodeling that accompanies endurance training [2].</p>
<p>The evolution of sports nutrition protein recommendations reflects methodological advances from <a href="/terms/nitrogen-balance/" class="term-link" data-slug="nitrogen-balance" title="nitrogen balance">nitrogen balance</a> studies to stable isotope tracer methodology to the more recent application of the indicator amino acid oxidation (IAAO) technique. These tools have progressively illuminated not only how much protein exercising individuals require to prevent deficiency (the minimum effective dose), but also how much — and what configuration of — protein optimally supports specific adaptive outcomes (the performance-optimizing dose) [3].</p>
<p>This position stand synthesizes the current evidence base across five major topic areas: protein requirements for exercising individuals; <a href="/terms/protein-timing/" class="term-link" data-slug="protein-timing" title="protein timing">protein timing</a> and distribution; protein sources and quality; special populations and contexts; and safety of higher protein intakes. Recommendations are graded by the strength of supporting evidence.</p>
<h2>Protein Requirements for Exercising Individuals</h2>
<h3>Beyond the RDA</h3>
<p>The current population-wide recommended dietary allowance (RDA) for protein is 0.8 g/kg body mass/day, established to cover the requirements of 97.5% of the sedentary population. This value was not derived from studies of exercising individuals and should not be applied as the reference standard for athletes. The metabolic demands of exercise — including increased myofibrillar protein turnover, mitochondrial protein remodeling, substrate oxidation of amino acids during prolonged exercise, and elevated <a href="/terms/connective-tissue/" class="term-link" data-slug="connective-tissue" title="connective tissue">connective tissue</a> synthesis — substantially increase daily protein requirements above this threshold [1].</p>
<h3>Evidence-Based Requirement Estimates</h3>
<p>Using <a href="/terms/nitrogen-balance/" class="term-link" data-slug="nitrogen-balance" title="nitrogen balance">nitrogen balance</a> methodology, early investigations from the 1980s and 1990s proposed protein intakes of approximately 1.2-1.4 g/kg/day for endurance athletes and 1.6-1.8 g/kg/day for strength athletes to maintain <a href="/terms/concentric-contraction/" class="term-link" data-slug="concentric-contraction" title="positive">positive</a> nitrogen balance. More recent stable isotope tracer studies and IAAO investigations have largely converged on similar estimates, though they suggest that even these values may represent conservative lower bounds for individuals seeking to maximize muscle anabolism rather than merely prevent deficiency [2].</p>
<p>The ISSN position is that exercising individuals require a minimum of <strong>1.4-2.0 g/kg/day</strong> to support training adaptations, with the following context-specific refinements:</p>
<ul>
<li><strong>Resistance training for <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="hypertrophy">hypertrophy</a>:</strong> 1.6-2.2 g/kg/day; evidence suggests minimal additional benefit above ~2.2 g/kg/day in most individuals with adequate total energy intake</li>
<li><strong>Endurance training:</strong> 1.2-1.6 g/kg/day to support mitochondrial turnover and attenuate amino acid oxidation during training</li>
<li><strong><a href="/terms/concurrent-training/" class="term-link" data-slug="concurrent-training" title="Concurrent training">Concurrent training</a>:</strong> 1.6-2.0 g/kg/day to address the demands of both resistance and endurance adaptive processes</li>
<li><strong><a href="/terms/caloric-deficit/" class="term-link" data-slug="caloric-deficit" title="Energy deficit">Energy deficit</a> conditions:</strong> 2.3-3.1 g/kg <a href="/terms/lean-body-mass/" class="term-link" data-slug="lean-body-mass" title="fat-free mass">fat-free mass</a> may be required to attenuate lean mass loss during caloric restriction [3]</li>
</ul>
<h3>Safety at Higher Intakes</h3>
<p>A common concern regarding high protein intakes is safety, particularly with respect to renal function. The ISSN position, consistent with other authoritative bodies, is that protein intakes up to 2.2 g/kg/day — and potentially higher — are safe in healthy individuals without pre-existing renal disease. Long-term studies in resistance-trained individuals consuming ≥3.0 g/kg/day have not demonstrated adverse effects on markers of renal function [1].</p>
<h2><a href="/terms/protein-timing/" class="term-link" data-slug="protein-timing" title="Protein Timing">Protein Timing</a> and Distribution</h2>
<h3>The Post-Exercise <a href="/terms/anabolic-window/" class="term-link" data-slug="anabolic-window" title="Anabolic Window">Anabolic Window</a></h3>
<p>The concept of a "post-exercise anabolic window" — a temporally restricted period following resistance exercise during which protein must be consumed to maximize <a href="/terms/muscle-protein-synthesis/" class="term-link" data-slug="muscle-protein-synthesis" title="MPS">MPS</a> — has generated considerable debate. Early formulations of this concept proposed a narrow 30-60 minute window, beyond which anabolic benefits were claimed to diminish sharply. More contemporary evidence indicates that the window is considerably wider: post-exercise muscle sensitization to dietary protein is elevated for at least 24 hours following resistance exercise in most trained individuals, with the acute elevation in MPS-stimulating responsiveness persisting for approximately 4-6 hours [1].</p>
<p>The practical implication is that while consuming protein in proximity to resistance training (within 1-2 hours before or after) is beneficial and likely optimal, missing this window by a modest period does not catastrophically compromise anabolic outcomes. Total daily protein intake and its distribution across meals remains more important as a determinant of 24-hour MPS than precise post-exercise timing in individuals who are otherwise meeting protein requirements across the day [2].</p>
<h3>Meal Distribution Recommendations</h3>
<p>The ISSN recommends distributing daily protein intake across 3-5 eating occasions, spaced approximately 3-4 hours apart, with each meal providing approximately 0.25-0.40 g/kg of body mass (equivalent to 20-40 g for most adults). This distribution strategy maximizes the number of anabolic feeding events throughout the day by repeatedly stimulating MPS above the <a href="/terms/leucine/" class="term-link" data-slug="leucine" title="leucine">leucine</a> threshold, rather than concentrating protein intake in one or two large boluses [1].</p>
<h3>Pre-Sleep Protein Ingestion</h3>
<p>Pre-sleep protein ingestion has emerged as a well-supported strategy for enhancing overnight muscle protein synthesis. The rationale is straightforward: the typical overnight fasting period (7-9 hours) represents a substantial interval during which inadequate amino acid availability limits MPS despite the anabolic hormonal environment of sleep. Ingestion of 30-40 g of <a href="/terms/casein/" class="term-link" data-slug="casein" title="casein">casein</a> protein (a slowly digested, micellar protein that releases amino acids gradually over 5-7 hours) 30-60 minutes before sleep sustains plasma amino acid concentrations throughout the night, driving measurably higher overnight MPS rates compared to non-supplemented controls [3].</p>
<p>Studies directly examining pre-sleep casein ingestion in resistance-trained individuals performing standardized exercise protocols have demonstrated improvements in <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="muscle hypertrophy">muscle hypertrophy</a> and strength gains over 12-week training periods compared to placebo, providing translational evidence for the acute MPS data.</p>
<h2>Protein Sources and Quality</h2>
<h3>Defining Protein Quality</h3>
<p>Protein quality is a composite construct reflecting the capacity of a dietary protein source to support <a href="/terms/nitrogen-balance/" class="term-link" data-slug="nitrogen-balance" title="nitrogen retention">nitrogen retention</a> and — in the sports nutrition context specifically — skeletal <a href="/terms/muscle-protein-synthesis/" class="term-link" data-slug="muscle-protein-synthesis" title="muscle protein synthesis">muscle protein synthesis</a>. The principal determinants of protein quality are: the essential amino acid (<a href="/terms/essential-amino-acids/" class="term-link" data-slug="essential-amino-acids" title="EAA">EAA</a>) content; the <a href="/terms/leucine/" class="term-link" data-slug="leucine" title="leucine">leucine</a> content per gram of total protein; the digestibility of the protein (fraction of ingested protein recovered from intestinal digestion); and the postprandial plasma amino acid kinetics (rapid vs. slow protein) [1].</p>
<p>Two formal scoring systems are commonly referenced: the Protein Digestibility-Corrected Amino Acid Score (PDCAAS) and its successor the Digestible Indispensable Amino Acid Score (DIAAS). Both systems compare a protein's EAA profile to a reference pattern and penalize for low digestibility. Animal-derived proteins generally score higher than plant proteins under both systems, reflecting higher EAA content, greater leucine density, and superior digestibility [2].</p>
<h3>Animal-Derived Protein Sources</h3>
<p><a href="/terms/whey-protein/" class="term-link" data-slug="whey-protein" title="Whey protein">Whey protein</a> — isolated from the aqueous component of cheese production — is considered the reference standard for exercise nutrition due to its rapid digestion kinetics, high leucine content (~11% by weight), and complete EAA profile. It produces sharp, transient elevations in plasma amino acids ideally suited to the post-exercise <a href="/terms/anabolic-window/" class="term-link" data-slug="anabolic-window" title="<a href="/terms/protein-timing/" class="term-link" data-slug="protein-timing" title="anabolic window">anabolic window</a>">anabolic window</a>. Whey concentrate, isolate, and hydrolysate forms differ in minor processing characteristics but produce broadly comparable MPS responses at equivalent leucine doses.</p>
<p><a href="/terms/casein/" class="term-link" data-slug="casein" title="Casein">Casein</a> protein digests slowly, producing sustained plasma amino acid elevations over 5-7 hours. This kinetic profile is ideally matched to extended fasting periods such as overnight sleep, where sustained amino acid availability is desired. Dietary casein sources include cottage cheese, Greek yogurt, and casein powder [3].</p>
<h3>Plant-Derived Protein Sources</h3>
<p>Plant proteins are increasingly important given the growth of plant-based dietary patterns in athletic populations. Soy protein is the most comprehensively studied plant protein, providing a complete EAA profile with adequate leucine content for MPS stimulation when consumed at sufficient doses (30 g per meal). Pea protein and rice protein are widely used alternatives; when combined in a 70:30 ratio, they approximate the EAA profile of whey. Emerging research suggests that well-designed plant protein formulations can produce comparable <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="muscle hypertrophy">muscle hypertrophy</a> to animal proteins over 12-week training periods when daily protein targets and leucine thresholds are met [1].</p>
<p>The ISSN position affirms that both animal and plant protein sources can adequately support muscle anabolism in exercising individuals, provided that total daily protein intake, leucine adequacy per meal, and appropriate dose targeting are achieved.</p>