Effects of carbohydrate quantity and glycemic index on resting metabolic rate and body composition during weight loss

OBJECTIVE: To examine the effects of diets varying in carbohydrate and glycemic index (GI) on changes in body composition, resting metabolic rate (RMR) and metabolic adaptation during and after weight loss. METHODS: Adults with obesity (n = 91) were randomized to one of four provided-food diets for 17 wk. Diets differed in percentage energy from carbohydrate (55% or 70%) and GI (low or high), but were matched for protein, fiber and energy. Body weight, body composition, RMR, and metabolic adaptation (measured RMR – predicted RMR) were measured during weight loss and subsequent weight stability. RESULTS: No effect of dietary carbohydrate content or GI on body weight loss or percentage of weight lost as fat mass was observed. Measured RMR was significantly lower (−226 kJ/d [95%CI: −314 kJ/d, −138 kJ/d] P < 0.001) than predicted RMR following weight loss, but this difference was attenuated after 5 wk weight stability. Metabolic adaptation did not differ by dietary carbohydrate content or GI, and was not associated with weight regain 12 mo later. CONCLUSION: Moderate-carbohydrate and low-GI diets did not preferentially reduce fat mass, preserve lean mass, or attenuate metabolic adaptation during weight loss compared to high-carbohydrate and high-GI diets.