Fatty acid oxidation is directly regulated by carbohydrate metabolism during exercise

Am J Physiol. 1997 Aug;273(2 Pt 1):E268-75. doi: 10.1152/ajpendo.1997.273.2.E268.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adipose Tissue / anatomy & histology
  • Adult
  • Blood Glucose / analysis
  • Caprylates / metabolism
  • Carbohydrate Metabolism*
  • Carbon Dioxide
  • Exercise*
  • Fatty Acids / metabolism*
  • Fatty Acids, Nonesterified / blood
  • Humans
  • Insulin / blood
  • Male
  • Muscles / metabolism
  • Oxidation-Reduction
  • Palmitates / metabolism
  • Respiration
  • Triglycerides / metabolism


  • Blood Glucose
  • Caprylates
  • Fatty Acids
  • Fatty Acids, Nonesterified
  • Insulin
  • Palmitates
  • Triglycerides
  • Carbon Dioxide
  • octanoic acid