Effects Of Carbohydrate Ingestion During Exercise On Substrate Utilization In Women Of Varying Body Composition.

Abstract

PURPOSE: To investigate the effects of consuming a carbohydrate (CHO) beverage (6% CHO) prior to and during exercise on fat and CHO oxidation during and after exercise in women of high fat >25% (HF) and low fat < 25% (LF) body composition. METHODS: Healthy, physically active young females (n = 18, age 18 to 40 y) were tested on 3 occasions. During session 1 air displacement plethysmography was used to determine % body fat (%FAT), fat-free mass (FFM), and fat mass (FM) and a graded exercise test was used to determine maximal oxygen consumption (VO2max). During the two treatment sessions, subjects preformed treadmill exercise for 45 minutes at 55% of VO2max. Immediately prior to exercise and at 15 minute intervals during exercise, subjects consumed a CHO beverage or placebo equal to 25% of a total fluid volume. The volume of fluid was equal to 17.1 ml/kg body mass (1 g CHO/ kg body mass). During exercise and for 2 h post-exercise, expired gases were collected to determine fat and CHO oxidation. A 2×2×4 mixed model ANOVA was used to analyze the data with significance set a P < 0.05. RESULTS: Women in the HF group were 32.4 ± 5.5% fat with a VO2max of 36.5 ± 7.5 ml/kg/min and women in the LF group were 19.3 ± 3.4% fat with a VO2max of 46.7 ± 4.3 ml/kg/min. Significant differences in CHO oxidation were found during exercise between groups (HF 1.42 g/min vs LF 1.79 g/min). A significant difference was found for %FAT in fat and CHO oxidation. LF women had significantly higher CHO oxidation (g/kg ffm/min) than HF women regardless of treatment or measurement time. HF women had significantly higher fat oxidation (g/min and g/kg ffm/min) than LF women regardless of treatment or measurement time. CONCLUSIONS: Body composition has a significant influence on substrate oxidation with high fat women having lower CHO oxidation and higher fat oxidation than low fat women. These data suggest that substrate supply has a strong influence on fat and carbohydrate oxidation in young physically active women. Supported by the Miami University Undergraduate Summer Scholars Program.