The adaptation of nutrient oxidation to nutrient intake on a high-fat diet.

Intervention studies have shown that the adaptation of fat oxidation to fat intake, when changing the dietary fat content, is not abrupt. This study was conducted to measure the time course of adaptation of oxidation rates to increases in the fat content of the diet, when feeding subjects at energy balance. Twelve healthy, non-obese males and females (age: 26 +/- 2, BMI: 21.4 +/- 0.5, habitual fat intake: 29 +/- 1% energy) consumed a low-fat diet for 6 days (days 1-6) followed by a high-fat diet for 7 days (day 7-13). Days 5-9 and day 13 were spent in a respiration chamber. After adjusting energy intake to 24h energy expenditure on day 5, subjects were in energy balance (range -0.15 to +0.23 kJ/day) on days 6-9 and day 13. Fat balance was zero on day 6 but became positive after changing to the high-fat diet (1.06 +/- 0.15, 0.75 +/- 0.15, and 0.55 +/- 0.14 MJ/day for days 7, 8, and 9 respectively, p. < 0.05), reaching a new balance on day 13, 7 days afterwards. Thus, in case of energy balance, lean subjects are capable of adjusting fat oxidation to fat intake within 7 days, when dietary fat content is increased.