title: Low-fat diet alters intramuscular substrates and reduces lipolysis and fat oxidation during exercise.
abstract: We determined whether a low-fat diet reduces intramuscular triglyceride (IMTG) concentration, whole body lipolyis, total fat oxidation, and calculated nonplasma fatty acid (FA) oxidation during exercise. Seven endurance-trained cyclists were studied over a 3-wk period during which time they exercised 2 h/day at 70% of maximum O2 uptake VO(2 max) and consumed approximately 4,400 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 lowered IMTG concentration and raised muscle glycogen concentration at rest (P < 0.05). Metabolism was studied during 1 h of exercise at 67% VO(2 max) 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 isotopically determined rates of plasma free fatty acid or glucose disappearance. Therefore, 2%FAT reduced calculated nonplasma FA oxidation by 40% in association with a 19% reduction in whole body lipolysis while increasing calculated 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 oxidation during exercise in the fasted state in association with a reduced concentration of intramuscular triglyceride.
authors.affiliation: Human Performance Laboratory, Department of Kinesiology and Health Education, University of Texas at Austin, Austin, TX 78712, USA. coyle@mail.utexas/edu
authors.forename: E F
authors.initials: EF
authors.lastname: Coyle
authors.forename: A E
authors.initials: AE
authors.lastname: Jeukendrup
authors.forename: M C
authors.initials: MC
authors.lastname: Oseto
authors.forename: B J
authors.initials: BJ
authors.lastname: Hodgkinson
authors.forename: T W
authors.initials: TW
authors.lastname: Zderic
mesh_terms: D000328:Adult; D001642:Bicycling; D001786:Blood Glucose / Q000378:metabolism; D001823:Body Composition; D001835:Body Weight; D018752:Diet, Fat-Restricted; D004040:Dietary Carbohydrates / Q000008:administration & dosage; D002149:Energy Intake; D015444:Exercise / Q000502:physiology*; D005215:Fasting; D005227:Fatty Acids / Q000378:metabolism; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D050356:Lipid Metabolism; D008066:Lipolysis; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D010807:Physical Endurance; D014280:Triglycerides / Q000378:metabolism
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates; D005227:Fatty Acids; D005230:Fatty Acids, Nonesterified; D014280:Triglycerides; D006003:Glycogen