Context: Weight loss elicits physiological adaptations relating to energy inta ke and expenditure that antagonize ongoing weight loss. Objective: To test wheth er dietary composition affects the physiological adaptations to weight loss, as assessed by resting energy expenditure. Design, Study, and Participants: A rando mized paralleldesign study of 39 over-weight or obese young adults aged 18 to 4 0 years who received an energy-restricted diet, either low-glycemic load or lo w-fat. Participants were studied in the General Clinical Research Centers of th e Brigham and Women’s Hospital and the Children’s Hospital, Boston, Mass, befo re and after 10%weightless. The study was conducted from January 4,2001, to May 6, 2003. Main Outcome Measures: Resting energy expenditure measured in the fast ing state by indirect calorimetry, body composition by dual-energy X-ray absor ptiometry, cardiovascular disease risk factors, and self-reported hunger. Resul ts: Resting energy expenditure decreased less with the low-glycemic load diet t han with the low-fat diet, expressed in absolute terms(mean[SE], 96 [24] vs 176 [27] kcal/d; P=.04) or as a proportion(5.9%[1.5%] vs 10.6%[1.7%]; P=.05). Pa rticipants receiving the low-glycemic load diet reported less hunger than those receiving the low-fat diet(P=.04). Insulin resistance(P=.01), serum triglyceri des(P=.01), C-reac-tive protein(P=.03), and blood pressure(P=.07 for both syst olic and diastolic) improved more with the low-gly-cemic load diet. Changes in body composition (fat and lean mass) in both groups were very similar(P=.85 and P=.45, respectively). Conclusions: Changes in dietary composition within prevai ling norms can affect physiological adaptations that defend body weight. Reducti on in glycemic load may aid in the prevention or treatment of obesity, cardiovas cular disease, and diabetes mellitus.
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