Carbohydrate intake and glycemic index affect substrate oxidation during a controlled weight cycle in healthy men

BACKGROUND/OBJECTIVES: Because both, glycemic index (GI) and carbohydrate content of the diet increase insulin levels and could thus impair fat oxidation, we hypothesized that refeeding a low GI, moderate-carbohydrate diet facilitates weight maintenance. SUBJECTS/METHODS: Healthy men (n = 32, age 26.0 +/- 3.9 years; BMI 23.4 +/- 2.0 kg/m(2)) followed 1 week of controlled overfeeding, 3 weeks of caloric restriction and 2 weeks of hypercaloric refeeding (+50, -50 and +50% energy requirement) with low vs high GI (41 vs 74) and moderate vs high CHO intake (50% vs 65% energy). We measured adaptation of fasting macronutrient oxidation and the capacity to supress fat oxidation during an oral glucose tolerance test. Changes in fat mass were measured by quantitative magnetic resonance. RESULTS: During overfeeding, participants gained 1.9 +/- 1.2 kg body weight, followed by a weight loss of 6.3 +/- 0.6 kg and weight regain of 2.8 +/- 1.0 kg. Subjects with 65% CHO gained more body weight compared with 50% CHO diet (P < 0.05) particularly with HGI meals (P < 0.01). Refeeding a high-GI diet led to an impaired basal fat oxidation when compared with a low-GI diet (P < 0.02), especially at 65% CHO intake. Postprandial metabolic flexibility was unaffected by refeeding at 50% CHO but clearly impaired by 65% CHO diet (P < 0.05). Impairment in fasting fat oxidation was associated with regain in fat mass (r = 0.43, P < 0.05) and body weight (r = 0.35; P = 0.051). CONCLUSIONS: Both higher GI and higher carbohydrate content affect substrate oxidation and thus the regain in body weight in healthy men. These results argue in favor of a lower glycemic load diet for weight maintenance after weight loss.