Protein nutrition for endurance athletes: A metabolic focus on promoting recovery and training adaptation

Updated Daily Protein Requirements for Endurance Athletes

• The current evidence supports a daily intake of approximately 1.8 g/kg of body mass for endurance athletes during typical training periods.
• Higher intakes (up to or exceeding 2.0 g/kg/day) are recommended during recovery days, periods of carbohydrate restriction, or energy deficit.
• This represents a substantial increase over the standard RDA (0.8 g/kg/day) and habitual intake (~1.5 g/kg/day) among endurance athletes.
• Protein requirements are elevated even more on rest days, reflecting the metabolic need for repair during recovery.

Per Meal and Temporal Protein Recommendations

• Post-exercise protein intake of ~0.5 g/kg body mass is suggested to support contractile protein remodeling.
• Moderate doses of 10–20 g of protein before or during exercise can mitigate muscle protein breakdown, especially in carbohydrate-restricted training, without impairing adaptive responses.
• Larger doses (30–45 g), particularly from high-quality protein sources, may be necessary to stimulate mitochondrial protein synthesis during recovery.
• Timing, distribution, and source of protein intake should be tailored based on training type and energy availability.

Carbohydrate-Restricted Training Increases Protein Needs

• Training under conditions of low carbohydrate availability increases amino acid oxidation and muscle protein breakdown.
• A daily protein intake of 1.95 g/kg body mass is suggested for athletes undergoing these types of sessions.
• Co-ingesting protein does not appear to blunt the molecular signaling benefits of low-CHO training, making it a valuable strategy to maintain net protein balance.

Protein Does Not Enhance Performance During Exercise When CHO Is Adequate

• Adding protein to carbohydrate-based sports drinks during endurance activity does not improve performance when carbohydrate needs are already met.
• However, protein may improve glycogen resynthesis when carbohydrate intake is suboptimal, making it useful in real-world scenarios where appetite or tolerance is limited.

Tolerating High Training Loads and Supporting Immune Function

• Higher protein intake (up to 3 g/kg/day) during intensified training phases helps preserve performance and reduces muscle soreness, psychological stress, and infection risk.
• Benefits were observed even when carbohydrate intake was suboptimal, highlighting protein’s role in supporting health and recovery under stress.

Addressing Research Gaps: Sex, Age, and Specific Adaptations

• Female athletes remain underrepresented in protein research. Evidence suggests women may require more protein during the luteal phase of the menstrual cycle.
• Research is also lacking for master athletes (older endurance populations) using contemporary methods like IAAO.
• Despite progress, optimal protein doses for mitochondrial adaptation remain unclear and should be a future research priority.

Practical Implications for Endurance Athletes and Practitioners

• Periodizing protein intake based on training intensity, carbohydrate availability, and recovery status can help optimize outcomes.
• For athletes with low energy intake or limited appetite, combining protein with carbohydrate in smaller meals may support recovery and glycogen resynthesis.
• Coaches, nutritionists, and athletes should be cautious not to under-fuel carbohydrate needs in favor of protein, especially during high-performance phases.