title: Carbohydrate metabolism during exercise in females: effect of reduced fat availability.
abstract: This study examined the effect of reduced plasma free fatty acid (FFA) availability on carbohydrate metabolism during exercise. Six untrained women cycled for 60 minutes at approximately 58% of maximum oxygen uptake after ingestion of a placebo (CON) or nicotinic acid (NA), 30 minutes before exercise (7.4 +/- 0.5 mg.kg(-1) body weight), and at 0 minutes (3.7 +/- 0.3 mg.kg(-1)) and 30 minutes (3.7 +/- 0.3 mg.kg(-1)) of exercise. Glucose kinetics were measured using a primed, continuous infusion of [6,6-(2)H] glucose. Plasma FFA (CON, 0.86 +/- 0.12; NA, 0.21 +/- 0.11 mmol.L(-1) at 60 minutes, P <.05) and glycerol (CON, 0.34 +/- 0.05; NA, 0.10 +/- 0.04 mmol.L(-1) at 60 minutes, P <.05) were suppressed throughout exercise. Mean respiratory exchange ratio (RER) during exercise was higher (P <.05) in NA (0.89 +/- 0.02) than CON (0.83 +/- 0.02). Plasma glucose and glucose production were similar between trials. Total glucose uptake during exercise was greater (P <.05) in NA (1,876 +/- 161 micromol.kg(-1)) than in CON (1,525 +/- 107 micromol.kg(-1)). Total fat oxidation was reduced (P <.05) by approximately 32% during exercise in NA. Total carbohydrate oxidized was approximately 42% greater (P <.05) in NA (412 +/- 40 mmol) than CON (290 +/- 37 mmol), of which, approximately 16% (20 +/- 10 mmol) could be attributed to glucose. Plasma insulin and glucagon were similar between trials. Catecholamines were higher (P <.05) during exercise in NA. In summary, during prolonged moderate exercise in untrained women, reduced FFA availability results in a compensatory increase in carbohydrate oxidation, which appears to be due predominantly to an increase in glycogen utilization, although there was a small, but significant, increase in whole body glucose uptake.
authors: School of Health Sciences, Deakin University, Burwood, Australia.
authors: K F
authors: KF
authors: Howlett
authors: L L
authors: LL
authors: Spriet
authors: M
authors: M
authors: Hargreaves
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D050260:Carbohydrate Metabolism; D018592:Cross-Over Studies; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000097:blood*; D005260:Female; D005498:Follicular Phase / Q000502:physiology; D005990:Glycerol / Q000097:blood; D006003:Glycogen / Q000378:metabolism; D006728:Hormones / Q000097:blood; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D009525:Niacin / Q000494:pharmacology*
chemical_list: D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D006728:Hormones; D009525:Niacin; D019344:Lactic Acid; D006003:Glycogen; D005990:Glycerol