PURPOSE: The ideal amount of protein intake for endurance athletes has been poorly investigated. The aim of our study was to evaluated the physiological impact of different dietary protein intakes on body composition and performance outcomes in a group of elite cyclists.
METHODS: Thirty-four elite cyclists (1600-1800 km/month) participated to the study. Subjects were divided in 4 groups with different levels of protein intake: normal (NP, 1.2 g/kg), moderate (MP, 1.6 g/kg), high (HP, 2.0 g/kg) or very high (VHP 2.4 g/kg)protein for 8 wk. In the diets fats were maintained constant whilst energy from carbohydrate and protein was modified to maintain an isocaloric diet. Body composition was assessed via Dual X Ray Absorptiometry (DXA) and via ultrasound to calculate cross sectional area (CSA) of the anterior thigh. VO2max, peak power output and 1 RM half squat test were also performed.
RESULTS: After two months both HP and VHP showed a significant improvement of 1 RM (HP pre 133±14 Kg vs post 141±12 Kg, p<0.001; VHP pre 137±12 Kg vs post 144±11 Kg, p<0.001), PPO (HP pre 505±78 W vs post 534±67 W, p<0.001; VHP pre 512±55 W vs post 541±76 W, p<0.001), and VO2max (HP pre 62.1±5.8 mlO2/Kg vs post 64.5±5.9 mlO2/Kg, p<0.001; VHP pre 61.2±5,5 mlO2/Kg vs post 64.1±7,6 mlO2/Kg, p<0.001), without differences between groups. There were no significant changes of 1 RM and VO2max for both NP and MP whilst NP showed a significant decrease of PPO. Both HP and VHP showed a significant increase of lean body mass (LBM) (HP pre 64.72±1.9 Kg vs post 65.99±2.2 Kg, p<0.001; VHP pre 65.52±2.0 Kg vs post 67.61±1.7 Kg) whilst both NP and MP showed a significant decrease (NP pre 63.31±2.1 Kg vs post 62.4±2.3, p<0.05; MP pre 66.88±1.8 Kg vs post 65.80±2.9). HP and VHP showed a significant increase of anterior thigh CSA (HP pre 50.5±7.8 cm2 vs post 53.4±6.7 cm2, p<0.001; VHP pre 51.2±5.5 cm2 vs post 54.1±7.6 cm2). No chnages of blood values are detected.
CONCLUSIONS: Our data suggest that an higher protein intake (2.0 and 2.4 g/Kg) may help elite cyclists to improve performance and to increase muscle mass without differences between the two levels of protein intake. Instead 1.2 and 1.6 g/Kg of protein seemed to be not sufficient and could impair performance and muscle mass.