Carbohydrate metabolism during exercise in females : effect of reduced fat availability

Howlett, Kirsten, Spriet, Lawrence and Hargreaves, Mark 2001, Carbohydrate metabolism during exercise in females : effect of reduced fat availability, Metabolism, clinical and experimental, vol. 50, no. 4, pp. 481-487, doi: 10.1053/meta.2001.21035.

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Title Carbohydrate metabolism during exercise in females : effect of reduced fat availability
Author(s) Howlett, KirstenORCID iD for Howlett, Kirsten
Spriet, Lawrence
Hargreaves, Mark
Journal name Metabolism, clinical and experimental
Volume number 50
Issue number 4
Start page 481
End page 487
Total pages 8
Publisher WB Saunders Co.
Place of publication Duluth, Minn.
Publication date 2001-04
ISSN 0026-0495
Keyword(s) adult
blood glucose
carbohydrate metabolism
fatty acids
follicular phase
lactic acid
Summary 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 [6,6-2H] 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 μmol·kg−1) than in CON (1,525 ± 107 μmol·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.
Language eng
DOI 10.1053/meta.2001.21035
Field of Research 110602 Exercise Physiology
HERDC Research category C1 Refereed article in a scholarly journal
Copyright notice ©2001, W.B. Saunders Company
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