Effects of aerobic exercise on energy expenditure and nitrogen balance during very low calorie dieting

Abstract

Aerobic exercise in addition to severe caloric restriction was studied for its effects on resting energy expenditure (REE), weight loss, and lean tissue preservation in adult women. A formula diet providing 1.5 g protein and 0.5 g carbohydrate (CHO) per kilogram of ideal body weight daily (mean intake 720 kcal/d) was given to 12 overweight inpatients for 4 to 5 weeks. Six subjects remained sedentary (group 1), while the other six subjects (group 2) performed supervised endurance exercise (a total of 27 hours at 50% of maximal oxygen uptake (V̇O 2max) over 4 weeks). Lean tissue preservation was excellent in both groups and was unaffected by the group 2 exercise regimen. Weight loss over 4 weeks in the two groups did not differ (group 1, 6.9 ± 0.7 kg; group 2, 6.5 ± 0.7 kg). The V̇O 2max was not increased after 4 weeks of exercise compared with controls. The resting oxygen consumption (rV̇O 2) of both groups declined 10% ( P < .001) in the first seven days of dieting. Thereafter the rV̇O 2 in group 1 remained stable, but a further 17% reduction occurred in group 2 ( P < .03) by the third week of exercise. The free triiodothyronine (fT 3) concentration also fell more in group 2 ( P < .05), suggesting a relationship between fT 3 and energy expenditure during severe caloric restriction. The ergometer exercise for up to two hours daily was well tolerated. The absence of either a training effect or accelerated weight loss in group 2 may be due to the limited duration (4 weeks) or intensity of the exercise. The significant reduction in rV̇O 2 as a measure of REE is both surprising and difficult to explain. The lack of objective benefits from aggressive aerobic exercise concurrent with a severely restricted diet suggests that these therapeutic modalities be employed sequentially, rather than simultaneously, in the multidisciplinary approach to obesity.