Fat oxidation in response to four graded energy challenges in younger and older women

We examined whether older individuals have an impairment in their ability to oxidize dietary fat, a factor that could help to explain age-associated weight gain. The subjects were 16 healthy younger and older women. Fat oxidation was determined by indirect calorimetry before and after consumption of four different test meals consumed > or = 5 d apart. The intervention meals contained 0, 1046, 2092, or 4184 kJ (simulating extended fasting, and consumption of a snack, a small meal, and a moderately large meal, respectively), with 35% of energy from fat. The duration of each measurement was the amount of time required for postprandial energy expenditure to return to the premeal fasting value. A total of 96 measurements were obtained, including duplicates for all meal sizes in the younger women (in the follicular and luteal phases of the menstrual cycle). Total postprandial fat oxidation increased in proportion to meal size in the younger subjects, but did not increase above that for the 2092-kJ meal in the older women. In addition, older subjects had significantly lower total fat oxidation after consumption of the 4184-kJ meal (781 compared with 1029 kJ/measurement, P < 0.02) and also significantly greater fat deposition (745 compared with 464 kJ/measurement, P < 0.02). These findings suggest that, relative to younger women, older women have a reduced ability to oxidize dietary fat when they consume large meals.