The purpose of this narrative review is to provide an evidence-based update on the protein needs of endurance athletes with a focus on high-quality metabolic studies conducted on the topics of recovery and training adaptation over the past decade. We use the term `protein needs` to delineate between the concepts of a daily protein requirement and per meal protein recommendations when devising scientific evidence-based protein guidelines for the endurance athlete to promote post-exercise recovery, enhance the adaptive response to endurance training and improve endurance performance. A habitual protein intake of 1.5 g/kg of body mass (BM)-1·day-1 is typical in male and female endurance athletes. Based on findings from a series of contemporary protein requirement studies, the evidence suggests a daily protein intake of ~ 1.8 g·kgBM-1·day-1 should be advocated for endurance athletes, with the caveat that the protein requirement may be further elevated in excess of 2.0 g·kgBM-1·day-1 during periods of carbohydrate-restricted training and on rest days. Regarding protein recommendations, the current lack of metabolic studies that determine the dose response of muscle protein synthesis to protein ingestion in relation to endurance exercise makes it difficult to present definitive guidelines on optimal per meal protein intakes for endurance athletes. Moreover, there remains no compelling evidence that co-ingesting protein with carbohydrate before or during endurance exercise confers any performance advantage, nor facilitates the resynthesis of liver or muscle glycogen stores during recovery, at least when carbohydrate recommendations are met. However, recent evidence suggests a role for protein nutrition in optimising the adaptive metabolic response to endurance training under conditions of low carbohydrate and/or energy availability that represent increasingly popular periodised strategies for endurance athletes. Key Points: 1. The indicator amino acid oxidation method offers the most contemporary technique for estimating the protein requirements of endurance athletes and is fundamental to recent advances in informing context-specific (i.e. during carbohydrate-restricted or low energy availability training) and individualised daily protein intake guidelines during training and rest days. 2. Based on contemporary studies utilising the indicator amino acid oxidation method, endurance athletes require a daily protein intake of 1.8 g·kg of body mass (BM)-1·day-1, which is 50% greater than sedentary adults, but should be further elevated to ~ 2.0 g·kgBM-1·day-1 during intensive training periods conducted under conditions of carbohydrate restriction and/or low energy availability and on rest days. 3. Preliminary evidence indicates that endurance athletes should target a per meal protein intake of ~ 0.5 g·kgBM-1 to maximally stimulate the synthesis of contractile muscle proteins during immediate post-exercise recovery. 4. Although awareness around the under-representation of female participants in sport nutrition research is beginning to improve, experimental studies designed to inform the protein needs of female endurance athletes remains a priority gap in the knowledge that warrants investigation.
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