Low-fat diet alters intramuscular substrates and reduces lipolysis and fatoxidation during exercise

We determined whether a low-fat diet reduces intramuscular triglyceride (IM TG) concentration, whole body lipolyis, total fat oxidation, and calculated nonplasma fatty acid (FA) oxidation during exercise. Seven endurance-train ed cyclists were studied over a 3-wk period during which time they exercise d 2 h/day at 70% of maximum O-2 uptake (V) over dot O-2max and consumed sim ilar to4,400 kcal/day. During the 1st wk, their fat intake provided 32% of energy. During the 2nd and 3rd wk, they were randomly assigned to eat 2 or 22% of energy from fat (2% FAT or 22% FAT). Compared with 22% FAT, 2% FAT l owered IMTG concentration and raised muscle glycogen concentration at rest (P< 0.05). Metabolism was studied during 1 h of exercise at 67% (V) over do tO(2max) performed in the fasted state. 2% FAT resulted in a 27% reduction (P< 0.05) in total fat oxidation vs. 22% FAT without altering the stable is otopically determined rates of plasma free fatty acid or glucose disappeara nce. Therefore, 2% FAT reduced calculated nonplasma FA oxidation by 40% in association with a 19% reduction in whole body lipolysis while increasing c alculated minimal muscle glycogen oxidation compared with 22% FAT (all P< 0 .05). In summary, an extremely low fat (2% of energy) and high-carbohydrate diet lowers whole body lipolysis, total fat oxidation, and nonplasma FA ox idation during exercise in the fasted state in association with a reduced c oncentration of intramuscular triglyceride.