Vogt, M., Puntschart, A., Howald, J., Mueller, B., Mannhart, C., Gfeller-Tuescher, L., Mullis, P., & Hoppeler, H. (2003). Effects of dietary fat on muscle substrates, metabolism and performance in athletes. Medicine and Science in Sports and Exercise, 35, 952-960.

Duathletes (N = 11) ingested high-fat (53% fat) or low-fat (17% fat) diets in a random cross-over experimental design. The vastus lateralis was the site of biochemical assays.

Oxidative capacity (volume of mitochondria per unit volume of muscle fiber), maximal power, VO2max, half-marathon running time, and a 20-min all-out bicycle ergometer ride, were similar under both regimens. Intramyocellular lipid was significantly higher after the high-fat condition. Blood lactate concentrations and respiratory exchange ratios were significantly lower after the high-fat diet at rest and during all sub-maximal workloads.

Implication. In trained athletes, high-fat diets increase intramyocellular lipid measures without compromising muscle glycogen stores. There was a metabolic shift to using more fat for energy supply. Performance was not affected by the high-fat diet. There was considerable intersubject variation in response to high- and low-fat diets.

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