title: Effect of gender on lipid kinetics during endurance exercise of moderate intensity in untrained subjects.
abstract: We evaluated lipid metabolism during 90 min of moderate-intensity (50% VO(2) peak) cycle ergometer exercise in five men and five women who were matched on adiposity (24 +/- 2 and 25 +/- 1% body fat, respectively) and aerobic fitness (VO(2) peak: 49 +/- 2 and 47 +/- 1 ml x kg fat-free mass(-1) x min(-1), respectively). Substrate oxidation and lipid kinetics were measured by using indirect calorimetry and [(13)C]palmitate and [(2)H(5)]glycerol tracer infusion. The total increase in glycerol and free fatty acid (FFA) rate of appearance (R(a)) in plasma during exercise (area under the curve above baseline) was approximately 65% greater in women than in men (glycerol R(a): 317 +/- 40 and 195 +/- 33 micromol/kg, respectively; FFA R(a): 652 +/- 46 and 453 +/- 70 micromol/kg, respectively; both P < 0.05). Total fatty acid oxidation was similar in men and women, but the relative contribution of plasma FFA to total fatty acid oxidation was higher in women (76 +/- 5%) than in men (46 +/- 5%; P < 0.05). We conclude that lipolysis of adipose tissue triglycerides during moderate-intensity exercise is greater in women than in men, who are matched on adiposity and fitness. The increase in plasma fatty acid availability leads to a greater rate of plasma FFA tissue uptake and oxidation in women than in men. However, total fat oxidation is the same in both groups because of a reciprocal decrease in the oxidation rate of fatty acids derived from nonplasma sources, presumably intramuscular and possibly plasma triglycerides, in women.
authors.affiliation: Center for Human Nutrition and Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: Bettina
authors.initials: B
authors.lastname: Mittendorfer
authors.forename: Jeffrey F
authors.initials: JF
authors.lastname: Horowitz
authors.forename: Samuel
authors.initials: S
authors.lastname: Klein
mesh_terms: D000328:Adult; D001823:Body Composition; D002153:Calorimetry, Indirect; D004837:Epinephrine / Q000097:blood; D005080:Exercise Test; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D005990:Glycerol / Q000008:administration & dosage / Q000378:metabolism / Q000493:pharmacokinetics; D006801:Humans; D007262:Infusions, Intravenous; D007328:Insulin / Q000097:blood; D050356:Lipid Metabolism; D008055:Lipids / Q000008:administration & dosage / Q000493:pharmacokinetics; D008297:Male; D009638:Norepinephrine / Q000097:blood; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D019308:Palmitic Acid / Q000008:administration & dosage / Q000378:metabolism / Q000493:pharmacokinetics; D005082:Physical Exertion / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology; D012737:Sex Factors
chemical_list: D005230:Fatty Acids, Nonesterified; D007328:Insulin; D008055:Lipids; D019308:Palmitic Acid; D005990:Glycerol; D009638:Norepinephrine; D004837:Epinephrine