METABOLIC FUEL UTILIZATION IN OBESE WOMEN BEFORE AND AFTER WEIGHT-LOSS

OBJECTIVE: To test the hypothesis that weight rebound following slimmi ng diets may be caused by an adaptive alteration in fuel utilisation i nvolving a suppression of fat oxidation thus favouring fat storage in adipose tissue. DESIGN: Repeat measurements before and after two 14 d cycles of controlled weight loss using a very low energy diet (1.9 MJ/ d). SUBJECTS: Eight moderately obese women (body weight: 85.6+/-10.1 k g, BMI: 31+/-2 kg/m(2), age: 42.6+/-10.1 years). MEASUREMENTS: Energy expenditure and substrate balances using 24-h whole-body indirect calo rimetry and naturally labelled C-13-glucose. RESULTS: Aggregate weight loss was 5.1+/-0.8 kg. Twenty-four hour energy expenditure declined b y 12% (8359+/-282 to 7366+/-191 kJ/d. p < 0.001). Net fat utilisation was not significantly depressed (4009+/-366 to 3613+/-191 kJ/d, NS), a nd the proportion of energy derived from fat was unchanged at 48.0% be fore weight loss and 49.0% after weight loss. CONCLUSION:The well-reco gnised phenomenon of reduced energy expenditure is unlikely to be a ma jor cause of weight regain. The results do not support the theory that altered fuel selection in post-obese subjects may be the cause of dif ficulty in maintaining weight loss.