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

Authors: KARL, JAMES - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; ROBERTS, SUSAN - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; SCHAEFER, ERNST - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; GLEASON, JOI - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; FUSS, PAUL - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; RASMUSSEN, HELEN - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; SALTZMAN, EDWARD - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; DAS, SAI KRUPA - Jean Mayer Human Nutrition Research Center On Aging At Tufts University

Submitted to: Obesity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2015
Publication Date: 11/4/2015
Citation: Karl, J.P., Roberts, S.B., Schaefer, E.J., Gleason, J.A., Fuss, P., Rasmussen, H., Saltzman, E., Das, S. 2015. Effects of carbohydrate quantity and glycemic index on resting metabolic rate and body composition during weight loss. Obesity. 23(11):2190-2198.

Interpretive Summary: Reduced carbohydrate and low-glycemic index diets have been suggested to enhance fat mass loss during weight loss and deter weight regain by attenuating reductions in energy expenditure during weight loss, but these proposed effects are uncertain because previous study designs were potentially confounded. In this study, 91 overweight and obese adults were provided one of four diets for 17 weeks. Diets differed in the percentage of energy from carbohydrates and glycemic index, but were matched for protein, fiber, and energy. Body weight, body composition, resting metabolic rate (RMR), and metabolic adaptation (measured RMR - predicted RMR) were measured during weight loss and subsequent weight stability. Results did not show any effect of dietary carbohydrate content or glycemic index on body weight loss or the percentage of weight lost as fat mass. Measured RMR was significantly lower than predicted RMR following weight loss, but this difference was attenuated after 5 weeks of weight stability. Metabolic adaptation did not differ by dietary carbohydrate content or glycemic index and was not associated with weight regain 12 months later. These findings suggest that when confounding dietary factors are controlled, moderate carbohydrate and low-GI diets do not preferentially reduce fat mass, preserve lean mass, or attenuate metabolic adaptation during weight loss compared to high-carbohydrate and high-glycemic index diets.

Technical Abstract: 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 (FM) was observed. Measured RMR was significantly lower (-226 kJ/day [95%CI: -314 to -138 kJ/d], P < 0.001) than predicted RMR following weight loss, but this difference was attenuated after 5 weeks of weight stability. Metabolic adaptation did not differ by dietary carbohydrate content or GI and was not associated with weight regain 12 months later. Conclusion: Moderate-carbohydrate and low-GI diets did not preferentially reduce FM, preserve lean mass, or attenuate metabolic adaptation during weight loss compared to high-carbohydrate and high-GI diets.