Protein Requirements in Male and Female Endurance Athletes

Participants will consume hourly (8 hours) isoenergetic, isonitrogenous beverages containing one of the three protein intakes (0.2g/kg/d, 1.2 g/kg/d, 2.0g/kg/d) assigned in a randomized order between the three metabolic trials. Drinks will be enriched with stable isotope \[13C\]phenylalanine. The use of stable isotope \[13C\]phenylalanine will allow for the determination of the fate of AA in the body (incorporation into body protein or oxidation) which can be used to determine protein (AA) requirements.