Inclusion Criteria:  Ages 18 - 30 and 70-89 yrs For the sarcopenic group, a SARC-F score of ≥ 4 at the screening visit  Exclusion Criteria:  History of diabetes that requires insulin for control of blood glucose History of malignancy or chemo/radiation therapy in the 6 months prior to enrollment History of gastrointestinal bypass/reduction surgery (Lapband, gastric sleeve, etc.) Pregnant females Unwilling to wear the breath-collection mask Subjects who cannot refrain from using protein or amino acid supplements for 7 days prior to Visit 2 Concomitant use of oral or injectable corticosteroids Concomitant use of testosterone, IGF-1, or similar anabolic agent Any other disease or condition that would place the subject at increased risk of harm if they were to participate, at the discretion of the study physician