The purpose of this study is to assess the optimal protein intake to maximize whole-body protein net balance in healthy adults. In a randomized, double-blinded, crossover design, 12 young, healthy adult males and females aged 18-35 years, will consume a test diet consisting of free amino acid mixtures based on milk protein that vary in protein content 7 separate acute metabolic trials. The main study endpoint is optimal protein intake based on the lowest protein intake that maximizes whole-body protein net balance.

Inclusion Criteria:

• Aged between 18-35 years
• BMI between 18.5-30 kg/m2
• Healthy, recreationally active (exercise at least once per two weeks and a maximum of four days per week)
• No physical limitations (i.e., able to perform all activities associated with daily living independently)

Exclusion Criteria:

• Smoking
• Diagnosed musculoskeletal disorders
• Use of any medications known to affect protein metabolism (i.e., corticosteroids, non-steroidal anti-inflammatories, or prescribed acne medications)
• Chronic use of gastric acid-suppressing medication or anti-coagulants
• Unstable weight over the last three months
• Diagnosed GI tract disorders or diseases
• Blood donation in the past 2 months
• Females: pregnancy