CHANGES IN FAT OXIDATION IN RESPONSE TO A HIGH-FAT DIET

Intervention studies have shown that the adaptation of fat oxidation t o fat intake, when the dietary fat content is changed, is not abrupt, This study was conducted to measure the time course of adaptation of o xidation rates to increases in the fat content of the diet while subje cts were fed at energy balance. Twelve healthy, nonobese males and fem ales [age: 26 +/- 2y, body mass index (in kg/m(2)): 21.4 +/- 0.5; and habitual fat intake: 29 +/- 1% of energy] consumed a low-fat diet for 6 d (days 1-6)followed by a high-fat diet for 7 d (days 7-13). Days 5- 9 and 13 were spent in a respiration chamber. After adjustment for ene rgy intake to 24-h energy expenditure on day 5, subjects were in energ y balance (range. -0.15 to 0.23 kJ/d) on days 6-9 and lj. Fat balance was zero on day 6 but became positive after subjects changed to the hi gh-fat diet(1.06 +/- 0.15, 0.75 +/- 0.15, and 0.55 +/ 0.14 MJ/d for da ys 7, 8, and 9, respectively, P < 0.05), reaching a new balance on day 13, 7 d afterward. In conclusion, when in energy balance, lean subjec ts are capable of adjusting fat oxidation to fat intake within 7 d of when dietary fat content is increased.