ROLE OF GLYCOGEN-LOWERING EXERCISE IN THE CHANGE OF FAT OXIDATION IN RESPONSE TO A HIGH-FAT DIET

One of the candidate factors for determining the increase of fat oxida tion after a switch from a reduced-fat diet to a high-fat diet is the size of the glycogen storage. Therefore, we studied the effect of low glycogen stores on fat oxidation after a switch from a reduced-fat die t to a high-fat diet. Twelve healthy, nonobese males and females (age: 22 +/- 1 yr,body mass index: 21.0 +/- 0.7, maximal power output: 254 +/- 11 W) consumed a reduced-fat (RF) diet (30, 55, and 15% of energy from fat, carbohydrate, and protein, respectively) three times a day a t home for 3 days (days 1-3). On two occasions subjects came to the la boratory on day 3 at 1500 to perform an exhaustive glycogen-lowering e xercise (EX), after which they went into the respiration chamber for a 36-h stay. On one occasion, subjects directly entered the respiration chamber at 1800 for a 36-h stay. In the respiration chamber they were given either a high-fat (HF) diet (60, 25, and 15% of energy from fat , carbohydrate, and protein, respectively) or a RF diet. In both cases they were fed at energy balance. All diets were consumed as breakfast , lunch, dinner, and two or more snacks per day. On the HF treatment, fat oxidation was below fat intake, indicating the slow change of oxid ation to intake on a HF diet. After the HF+EX treatment, however, fat oxidation matched fat intake. In conclusion, lean subjects are capable of rapidly adjusting fat oxidation to fat intake when glycogen stores are lowered by exhaustive exercise.