Abstract

We compared the effects of consuming a 2-day low-carbohydrate (CHO) diet (low-CHO; 20% CHO, 40% protein, 40% fat) versus an isocaloric 2-day moderate-CHO diet (mod-CHO; 55% CHO, 15% protein, 30% fat) on substrate oxidation during and after exercise in ten active, young women. Subjects were 24.9 ± 6.2% body fat with a VO(2max) of 68.8 ± 13.8 ml/kg FFM/min. For 2 days prior to exercise, subjects consumed either the mod-CHO or the low-CHO diet and then completed treadmill exercise at 55% of VO(2max) until 350 kcal of energy was expended. During exercise and for 2 h post-exercise, expired gases were analyzed to determine oxidation rates for CHO (CHO-OX) and fat (FAT-OX). Significant differences (p < 0.05) were found between diets for CHO-OX and FAT-OX (mg/kg FFM/min) during exercise, 1 h post-ex, and 2 h post-ex. During exercise, FAT-OX was higher (low-CHO 8.7 ± 2.2 vs. mod-CHO 6.2 ± 2.2) and CHO-OX was lower (low-CHO 25.1 ± 5.6 vs. mod-CHO 31.1 ± 6.2) following the low-CHO diet. A similar trend was observed during 1 h post-ex for FAT-OX (low-CHO 2.2 ± 0.5 vs. mod-CHO 1.6 ± 0.5) and CHO-OX (low-CHO 2.5 ± 1.2 vs. mod-CHO 4.1 ± 1.9), as well as 2 h post-ex for FAT-OX (low-CHO vs. 1.9 ± 0.5 mod-CHO 1.7 ± 0.4) and CHO-OX (low-CHO 2.5 ± 0.9 vs. mod-CHO 3.1 ± 1.1). Significant positive correlations were observed between VO(2max) and CHO-OX during exercise and post-exercise, as well as significant negative correlations between VO(2max) and FAT-OX post-exercise in the low-CHO condition. Waist circumference and FAT-OX exhibited a significant negative correlation during exercise in the low-CHO condition. Dietary macronutrient intake influenced substrate oxidation in active young women during and after moderate intensity exercise.