Nutrition for athletes is a cornerstone of athletic performance. Appropriate dietary intake not only provides the energy required for training and competition but also supports recovery, muscle adaptation, immune function, and long-term health. While both strength and endurance athletes require adequate energy and nutrient intake, their nutritional priorities differ according to the physiological demands of their sport. Inadequate nutrition can impair performance and increase the risk of Relative Energy Deficiency in Sport (RED-S), a syndrome that affects athletes of all sexes and competitive levels. This article reviews current evidence regarding nutrition for athletes, with a focus on evidence-based nutrition strategies for strength and endurance athletes and the importance of recognizing and preventing RED-S.
Inadequate nutrition can impair performance and increase the risk of Relative Energy Deficiency in Sport (RED-S), a syndrome that affects athletes of all sexes and competitive levels. This article reviews current evidence regarding nutrition strategies for strength and endurance athletes and highlights the importance of recognizing and preventing RED-S.
Nutrition for Strength Training: Build Muscle Smarter
Strength and power athletes rely on resistance exercise to stimulate skeletal muscle hypertrophy, neural adaptations, and improvements in maximal force production. These physiological adaptations require sufficient energy intake alongside optimal protein and carbohydrate consumption.
Energy Availability
Maintaining adequate energy availability is essential for muscle growth and recovery. Chronic energy restriction reduces muscle protein synthesis, impairs hormonal function, and limits training adaptations. Athletes attempting to lose body fat should avoid prolonged severe energy deficits, as these may compromise lean mass and performance (1).
Protein Requirements
Protein is the primary nutrient supporting muscle repair and hypertrophy. Current evidence recommends daily protein intakes of approximately 0.73–1.0 g/lb/day for athletes undertaking resistance training, distributed evenly in meals throughout the day (2). Consuming high-quality protein within the hours following resistance exercise further supports muscle protein synthesis, although total daily protein intake remains the most important determinant of adaptation (2).
Carbohydrates
Although carbohydrates are often associated with endurance performance, they are equally important for resistance training. Muscle glycogen provides fuel for repeated high-intensity efforts, and inadequate carbohydrate intake may reduce training volume and impair recovery. Athletes completing frequent or high-volume resistance sessions generally benefit from consuming 1.36–2.72 g/lb/day, depending on training demands (3).
Dietary Fat and Micronutrients
Dietary fat should provide approximately 20–35% of total energy intake to support hormone production and facilitate absorption of fat-soluble vitamins. Adequate calcium, vitamin D and iron status are also important, particularly for athletes undertaking heavy training loads or restricting energy intake (1).
Nutrition for Athletes: Fueling Endurance Training
Nutrition for athletes is especially important for endurance athletes, who experience substantially greater energy expenditure than strength athletes and therefore require careful nutritional planning to sustain prolonged exercise, maximise recovery, and maintain health.
Carbohydrate: The Primary Fuel Source
Carbohydrates remain the most important nutrient for endurance performance. Glycogen depletion contributes significantly to fatigue during prolonged exercise. Current sports nutrition guidelines recommend carbohydrate intake according to training volume:
- 2.3–3.2 g/lb/day for moderate training
- 2.7–4.5 g/lb/day for high-volume endurance training
- Up to 3.6–5.4 g/lb/day during periods of very high training loads or carbohydrate loading before competition (3).
During endurance events lasting longer than 60–90 minutes, consuming 30–90 g of carbohydrate per hour improves exercise capacity and delays fatigue, particularly when multiple transportable carbohydrates such as glucose and fructose are used (3).
Protein
Although endurance exercise places less emphasis on muscle hypertrophy, adequate protein remains essential for repairing exercise-induced muscle damage, promoting mitochondrial adaptations, and supporting immune function. Daily intakes of 0.54–0.91 g/lb/day are generally recommended depending on training intensity and energy availability (2).
Hydration
Fluid losses exceeding approximately 2% of body mass can impair endurance performance, thermoregulation, and cognitive function. Hydration strategies should therefore be individualized according to sweat rate, environmental conditions, and exercise duration. Replacing both fluid and sodium losses during prolonged exercise assists in maintaining cardiovascular function and reduces the risk of dehydration (3).
Recovery Nutrition
Recovery nutrition should focus on replenishing glycogen stores and stimulating muscle repair. Consuming carbohydrate together with approximately 20–40 g of high-quality protein within the recovery period enhances glycogen resynthesis and muscle recovery, particularly when multiple training sessions occur within a short timeframe (2,3).
Relative Energy Deficiency in Sport (RED-S)
Relative Energy Deficiency in Sport (RED-S) is a clinical syndrome caused by low energy availability, where dietary energy intake is insufficient to support both exercise demands and normal physiological function (4). Understanding nutrition for athletes is essential in preventing RED-S, as appropriate energy intake and nutrient timing help support training demands, recovery, and long-term health.
Originally recognized as the Female Athlete Triad, RED-S is now understood to affect athletes of all sexes participating across a wide range of sports. Endurance athletes, athletes in weight-sensitive sports, and individuals with high training volumes are particularly vulnerable (4,5). Proper nutrition for athletes plays a critical role in maintaining adequate energy availability and reducing the risk of performance decline, impaired recovery, and health consequences associated with RED-S.
Relative Energy Deficiency in Sport (RED-S) is a clinical syndrome caused by low energy availability, where dietary energy intake is insufficient to support both exercise demands and normal physiological function (4). Understanding nutrition for athletes is essential in preventing RED-S, as appropriate energy intake and nutrient timing help support training demands, recovery, and long-term health.
Originally recognized as the Female Athlete Triad, RED-S is now understood to affect athletes of all sexes participating across a wide range of sports. Endurance athletes, athletes in weight-sensitive sports, and individuals with high training volumes are particularly vulnerable (4,5). Proper nutrition for athletes plays a critical role in maintaining adequate energy availability and reducing the risk of performance decline, impaired recovery, and health consequences associated with RED-S.(4,5).
Health Consequences
Low energy availability disrupts multiple physiological systems, including:
- Endocrine function
- Bone metabolism
- Immune function
- Cardiovascular health
- Gastrointestinal function
- Psychological wellbeing
- Reproductive health
These alterations increase the risk of stress fractures, illness, fatigue, menstrual dysfunction, reduced testosterone, impaired recovery, and decreased training adaptations (4–6).
Performance Consequences
From a performance perspective, RED-S may result in:
- Reduced endurance capacity
- Loss of strength and power
- Impaired concentration
- Slower recovery
- Increased injury rates
- Reduced training consistency
Importantly, athletes may continue training while unknowingly experiencing chronic low energy availability, leading to progressive declines in both health and performance (4,6).
Prevention
Preventing RED-S requires education and early identification. Practical prevention strategies include:
- Matching energy intake with training load.
- Avoiding prolonged restrictive dieting during heavy training periods.
- Consuming sufficient carbohydrates to support exercise demands.
- Prioritizing adequate daily protein intake.
- Monitoring body weight, menstrual function, recovery, and recurrent injuries.
- Seeking assessment from a sports dietitian or sports medicine physician when symptoms of low energy availability develop.
Early intervention can restore physiological function and minimise long-term health consequences (4–6).
Conclusion
Optimal nutrition is fundamental for both strength and endurance athletes. Resistance-trained athletes require sufficient protein and energy to maximize muscle adaptation, while endurance athletes depend heavily on carbohydrate availability to sustain prolonged exercise and optimize recovery. Across all sporting disciplines, maintaining adequate energy availability is essential not only for performance but also for protecting long-term health. Awareness of RED-S has increased substantially over recent years, reinforcing the importance of comprehensive nutritional support throughout training and competition. Individualized nutrition plans for athletes developed in collaboration with qualified sports dietitians remain the gold standard for supporting athletic performance while reducing the risk of nutritional deficiencies and energy imbalance.
References
- Kerksick CM, Arent S, Schoenfeld BJ, et al. International Society of Sports Nutrition position stand: nutrient timing. J Int Soc Sports Nutr. 2022;19(1):1–88.
- Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr. 2025;22:2450277.
- Burke LM, Whitfield J, Heikura IA, Ross MLR. Carbohydrates for training and competition. J Sports Sci. 2022;40(1):1–16.
- Cabre HE, Moore SR. Relative Energy Deficiency in Sport (RED-S): scientific, clinical, and practical implications for the female athlete. Dtsch Z Sportmed. 2022;73(7):225–234.
- Coelho AR, Cardoso G, Brito ME, Gomes IN, Cascais MJ. The Female Athlete Triad/Relative Energy Deficiency in Sports (RED-S). Rev Bras Ginecol Obstet. 2021;43(5):395–402.
- Stellingwerff T, Heikura IA, Meeusen R, Bermon S, Seiler S, Mountjoy ML, et al. Overtraining syndrome and Relative Energy Deficiency in Sport (RED-S): shared pathways, symptoms and complexities. Sports Med. 2021;51(11):2251–2280.
