Creatine supplementation has no effect on human muscle protein turnover at rest in the postabsorptive or fed states

1 Université catholique de Louvain, 2 Université Libre de Bruxelles, Brussels 1200, Belgium; 3 Karolinska Institute, Stockholm 11440, Sweden; 4 Université de Poitiers, Poitiers 86034, France; 5 Massachusetts Institute of Technology, Cambridge, Massachusetts 02142; and 6 University of Dundee, Dundee DD1 4HN, Scotland Dietary creatine supplementation is associated with increases in muscle mass, but the mechanism is unknown. We tested the hypothesis that creatine supplementation enhanced myofibrillar protein synthesis (MPS) and diminished muscle protein breakdown (MPB) in the fed state. Six healthy men (26 ± 7 yr, body mass index 22 ± 4 kg/m 2 ) were studied twice, 2-4 wk apart, before and after ingestion of creatine (21 g/day, 5 days). We carried out two sets of measurements within 5.5 h of both MPS (by incorporation of [1- 13 C]leucine in quadriceps muscle) and MPB (as dilution of [1- 13 C]leucine or [ 2 H 5 ]phenylalanine across the forearm); for the first 3 h, the subjects were postabsorptive but thereafter were fed orally (0.3 g maltodextrin and 0.083 g protein · kg body wt 1 · h 1 ). Creatine supplementation increased muscle total creatine by ~30% ( P