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A field study was performed to investigate the acute influence of a milk protein hydrolysate supplemented drink (CHO+PRO) on metabolism during and after a marathon run compared to the same drink without protein (CHO). Carbohydrate metabolites and hormones were not influenced by CHO+PRO. Levels of plasma free fatty acids were significantly lower and levels of urea and most amino acids were significantly higher with CHO+PRO. Sweat urea and ammonia nitrogen excretion during the run as well as urinary 3-methylhistidine excretion during the entire exercise day was similar with both treatments. Urinary total nitrogen was significantly increased and urinary pH decreased with CHO+PRO. It was concluded that the supplemented protein was absorbed and probably at least partially oxidized during the run and that no obvious negative metabolic effects occurred. CHO+PRO did not acutely affect myofibrillar protein breakdown as assessed by the 3-methylhistidine method: however, total body protein breakdown was not measured.

P.C. Colombani, E. Kovacs, P. Frey-Rindova, and C. Wenk are with INW Nutrition Biology, Swiss Federal Institute of Technology, CH-8092 Zurich, Swilzerland. W. Frey is with Schulthess Hospital, Department of Sports Medicine, CH-8008 Zurich, Switzerland. W. Langhans and M. Arnold are with INW Physiology, Swiss Federal Institute of Technology, CH-8092 Zurich, Switzerland. Direct correspondence to P.C. Colombani, Swiss Federal Institute of Technology, INW Nutrition Biology, ETH Zentrum - LFW A 33, CH-8092 Zurich, Switzerland (e-mail: paolo.colombani@inw.agrl.ethz.ch).