High-protein and acidogenic diets induce hypercalciuria. Foods or supplements with excess sulfur-containing amino acids increase endogenous sulfuric acid production, and therefore have the potential to increase calcium excretion and alter bone metabolism. In this study, effects of an amino acid/carbohydrate supplement on bone resorption were examined during bed rest. Thirteen subjects were divided at random into 2 groups: a control group (CON, n = 6) and an amino acid/carbohydrate supplemented group (AA, n = 7) who consumed an extra 49.5 g essential amino acids and 90 g carbohydrate per day for 28 d. Urine was collected for ntelopeptide (NTX), deoxypyridinoline (DPD), calcium, and pH determinations. Bone mineral content (BMC) was determined and potential renal acid load (PRAL) was calculated. Bonespecific alkaline phosphatase (BSAP) was measured in serum samples collected on day 1 (immediately before bed rest) and on day 28. PRAL was higher in the AA group than in the CON group during bed rest (P < 0.05). For all subjects, during bed rest urinary NTX and DPD concentrations were greater than pre-bed rest levels (P < 0.05). Urinary NTX and DPD tended to be higher in the AA group (P = 0.073 and P = 0.056, respectively). During bed rest, urinary calcium was greater than baseline levels (P < 0.05) in the AA group but not the CON group. Total BMC was lower after bed rest than before bed rest in the AA group but not the CON group (P < 0.05). During bed rest, urinary pH decreased (P < 0.05), and was lower in the AA group than the CON group. These data suggest that bone resorption increased, without changes in bone formation, in the AA group.