Metabolic Responses To A Single Low-carbohydrate And Low-fat Meal At Rest And During Exercise In Adult Females

Abstract

PURPOSE: The present study examined the metabolic response to a single low-carbohydrate (LC) and low-fat (LF) meal at rest and during exercise in females. METHODS: All data are reported as the mean + standard deviation. Subjects included 8 premenopausal females who engaged in aerobic activity for > 3 days/week for at least 6 months (age 33.0 + 6.3 years, BMI 26.8 + 3.5 kg/m2, body fat 30.9 + 6.1%, and peak oxygen consumption (VO2peak) 41.8 + 5.7 ml/kg/min). Subjects completed a LC and LF testing session administered in random order and after a 12 hr fast. Respiratory gas exchange (RER) measurements were taken for 20 min fasted before the test meal was consumed, for 55 min postprandial (PP), and during 30 min of treadmill exercise performed at 60 to 65% of VO2peak. Blood was collected for assessment of glucose (G), insulin (IN), triglycerides (TG), and free fatty acids (FFA) during the final 10 min of the fasting and PP time periods and immediately post-exercise (PE). G, FFA, and TG were analyzed using enzymatic assays. IN was analyzed using the ELISA technique. The LF meal provided 396 kcal (78% carbohydrate, 7% fat, and 15% protein). The LC meal provided 392 kcal (15% carbohydrate, 68% fat, and 18% protein). Repeated Measures Factorial ANOVAs were computed for LC and LF over time. RESULTS: No significant differences (p > 0.05) existed between test meals for fasting values of RER, G, IN, TG, or FFA. PP IN (µU/ml) levels were significantly lower (p < 0.05) following LC compared to LF (10.7 + 6.1 vs. 26.0 + 21.0). PE FFA (mEq/L) levels were significantly greater (p < 0.05) following LC (1.1 + 0.3 vs. 0.5 + 0.3). PE TG (mg/dL) levels were significantly greater (p < 0.05) following LC (152.0 + 53.1 vs. 114.4 + 40.9). RER was significantly lower (p < 0.05) from 0 to 25 min PP and from 25 to 55 min PP after LC (0.72 + 0.04 vs. 0.80 + 0.04 and 0.75 + 0.03 vs. 0.86 + 0.04). RER during exercise was significantly lower (p < 0.05) after LC (0.81 + 0.04 vs. 0.86 + 0.04). CONCLUSIONS: In moderately active adult females, ingestion of a single LC meal resulted in greater lipid oxidation at rest and during exercise as compared to a single LF meal. Although macronutrient distribution appears to have dictated substrate utilization in the present study, more research is needed regarding the long-term effects of macronutrient redistribution with and without exercise on substrate utilization.