Objective: To investigate 24 h energy expenditure (24 h EE) and substrate oxidations in overweight and obese subjects before and after 6 months' ad libitum intake of a low-fat, high-simple carbohydrate diet (SCHO), a low-fat, high-complex carbohydrate diet (CCHO), or a habitual control diet (CD).
Subjects: Twenty-four healthy overweight and obese subjects (11 males and 13 females; body mass index 30.7+/-0.6 kg/m(2); age 42.2+/-1.8 y).
Measurements: Twenty-four hour EE, substrate oxidation rates and spontaneous physical activity (SPA) measured in a respiration chamber, and food intake.
Results: After the intervention no differences were seen in 24 h EE, postprandial thermogenesis, basal metabolic rate or SPA. Carbohydrate oxidation, adjusted for energy balance, increased on both carbohydrate-rich diets (SCHO 13.0%, CCHO 11.5%) and decreased on the CD diet (6.5%); however, the changes were not significantly different between diets. The opposite pattern was seen for fat oxidation, which increased by 2.9% on the CD diet and decreased by 17.1 and 25.6% on the SCHO and CCHO, respectively. The changes only differed between the CD and CCHO diet (P=0.03).
Conclusion: Six months' ad libitum intake of a diet rich in simple or complex carbohydrates or a habitual diet induced a shift in the oxidation pattern to closely reflect the diet composition in overweight and obese subjects. No differences between diets were seen in 24 h EE.