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

Background: Dietary fat contents are highly variable. Failure to compensate for the positive fat balance that occurs during the shift to a high-fat, l ow-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 o f fat oxidation during adaptation to an isoenergetic high-fat, low-carbohyd rate diet. Design: After a 5-d control diet, dietary fat was increased from 37% of ene rgy to 50% of energy for 4 d in 6 healthy, young lean men. Respiratory quot ient and substrate macronutrient oxidation and balance were measured in a r espiratory chamber. Fasting concentrations of insulin, glucose, and triacyl glycerol; maximal oxygen consumption (VO2 max) during treadmill exercise; a nd free-living energy expenditure were determined. Body fat was measured by dual-energy X-ray absorptiometry and visceral adipose tissue by computeriz ed tomography. Results: Compared with the baseline diet, the high-fat, low-carbohydrate di et resulted in positive fat and protein balances and a negative carbohydrat e balance. Insulin concentration and the postabsorptive respiratory quotien t were positively correlated with the fat balance during the high-fat, low- carbohydrate diet, whereas VO2 max during treadmill exercise was negatively related to fat balance. With use of stepwise regression, VO2 max was the b est predictor of fat balance. There was a negative correlation between fat balance and carbohydrate balance (r(2) = 0.88). Conclusion: Both baseline insulin concentration and VO2 max during treadmil l exercise predict fat balance during the shift to a high-fat diet under is oenergetic conditions.