title: Fatty acid oxidation is directly regulated by carbohydrate metabolism during exercise.
abstract: We determined whether increased glycolytic flux from hyperglycemia and hyperinsulinemia directly reduces fatty acid oxidation during exercise. Fatty acid oxidation rates were measured during constant-rate intravenous infusion of trace amounts of a long-chain fatty acid ([1-13C]palmitate; Pal) vs. a medium-chain fatty acid ([1-13C]octanoate; Oct). Six endurance-trained men cycled for 40 min at 50% of maximal O2 uptake 1) after an overnight fast ("fasting") and 2) after ingestion of 1.4 g/kg of glucose at 60 min and again 10 min before exercise (Glc). Glc caused hyperinsulinemia, a preexercise blood glucose of 6 mM, and a 34% reduction in total fat oxidation during exercise due to an approximately equal reduction in oxidation of plasma-free fatty acids (FFA) and intramuscular triglycerides (all P < 0.05). Oxidation of Pal was significantly reduced during Glc compared with fast (i.e., 70.0 +/- 4.1 vs. 86.0 +/- 1.9% of tracer infusion rate; P < 0.05). However, Glc had no effect on Oct oxidation, which is apparently not limited by mitochondrial transport. Furthermore, Glc reduced plasma FFA appearance 36% (P < 0.05), indicating a coordination of effects on adipose tissue and muscle. In summary, substrate oxidation during exercise can be regulated by increased glycolytic flux that is accompanied by a direct inhibition of long-chain fatty acid oxidation. These observations indicate that carbohydrate availability can directly regulate fat oxidation during exercise.
authors.affiliation: Department of Human Biology, University of Limburg, Maastricht, The Netherlands.
authors.forename: E F
authors.initials: EF
authors.lastname: Coyle
authors.forename: A E
authors.initials: AE
authors.lastname: Jeukendrup
authors.forename: A J
authors.initials: AJ
authors.lastname: Wagenmakers
authors.forename: W H
authors.initials: WH
authors.lastname: Saris
mesh_terms: D000273:Adipose Tissue / Q000033:anatomy & histology; D000328:Adult; D001786:Blood Glucose / Q000032:analysis; D002210:Caprylates / Q000378:metabolism; D050260:Carbohydrate Metabolism; D002245:Carbon Dioxide; D015444:Exercise; D005227:Fatty Acids / Q000378:metabolism*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006801:Humans; D007328:Insulin / Q000097:blood; D008297:Male; D009132:Muscles / Q000378:metabolism; D010084:Oxidation-Reduction; D010168:Palmitates / Q000378:metabolism; D012119:Respiration; D014280:Triglycerides / Q000378:metabolism
chemical_list: D001786:Blood Glucose; D002210:Caprylates; D005227:Fatty Acids; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D010168:Palmitates; D014280:Triglycerides; D002245:Carbon Dioxide; C031492:octanoic acid