Fat and carbohydrate balances during adaptation to a high-fat diet

Abstract

Background: Dietary fat contents are highly variable. Failure to compensate for the positive fat balance that occurs during the shift to a high-fat, low-carbohydrate diet by increasing energy expenditure or by decreasing food intake may result in the gain of fat mass. Objective: The objective of this study was to investigate the time course of fat oxidation during adaptation to an isoenergetic high-fat, low-carbohydrate diet. Design: After a 5-d control diet, dietary fat was increased from 37% of energy to 50% of energy for 4 d in 6 healthy, young lean men. Respiratory quotient and substrate macronutrient oxidation and balance were measured in a respiratory chamber. Fasting concentrations of insulin, glucose, and triacylglycerol; maximal oxygen consumption (V̇O₂max) during treadmill exercise; and free-living energy expenditure were determined. Body fat was measured by dual-energy X-ray absorptiometry and visceral adipose tissue by computerized tomography. Results: Compared with the baseline diet, the high-fat, low-carbohydrate diet resulted in positive fat and protein balances and a negative carbohydrate balance. Insulin concentration and the postabsorptive respiratory quotient were positively correlated with the fat balance during the high-fat, low-carbohydrate diet, whereas V̇O₂max during treadmill exercise was negatively related to fat balance. With use of stepwise regression, V̇O₂max was the best predictor of fat balance. There was a negative correlation between fat balance and carbohydrate balance (r² = 0.88). Conclusion: Both baseline insulin concentration and V̇O₂max during treadmill exercise predict fat balance during the shift to a high-fat diet under isoenergetic conditions.