A Reduced–Glycemic Load Diet in the Treatment of Adolescent Obesity

BACKGROUND: The incidence of type 2 diabetes increases markedly for obese children after puberty. However, the effect of dietary composition on body weight and diabetes risk factors has not been studied in adolescents. OBJECTIVE: To compare the effects of an ad libitum, reduced-glycemic load (GL) diet with those of an energy-restricted, reduced-fat diet in obese adolescents. DESIGN: Randomized control trial consisting of a 6-month intervention and a 6-month follow-up. MAIN OUTCOME MEASURES: Body composition (body mass index BMI; calculated as weight in kilograms divided by the square of height in meters and fat mass) and insulin resistance (homeostasis model assessment) were measured at 0, 6, and 12 months. Seven-day food diaries were used as a process measure. SUBJECTS: Sixteen obese adolescents aged 13 to 21 years. Intervention Experimental (reduced-GL) treatment emphasized selection of foods characterized by a low to moderate glycemic index, with 45% to 50% of energy from carbohydrates and 30% to 35% from fat. In contrast, conventional (reduced-fat) treatment emphasized selection of low-fat products, with 55% to 60% of energy from carbohydrates and 25% to 30% from fat. RESULTS: Fourteen subjects completed the study (7 per group). The GL decreased significantly in the experimental group, and dietary fat decreased significantly in the conventional group (P<.05 for both). At 12 months, mean +/- SEM BMI (-1.3 +/- 0.7 vs 0.7 +/- 0.5; P =.02) and fat mass (-3.0 +/- 1.6 vs 1.8 +/- 1.0 kg; P =.01) had decreased more in the experimental compared with the conventional group, differences that were materially unchanged in an intention-to-treat model (n = 16) (BMI, P =.02; fat mass, P =.01). Insulin resistance as measured by means of homeostasis model assessment increased less in the experimental group during the intervention period (-0.4 +/- 0.9 vs 2.6 +/- 1.2; P =.02). In post hoc analyses, GL was a significant predictor of treatment response among both groups (R2 = 0.51; P =.006), whereas dietary fat was not (R2 = 0.14; P =.22). CONCLUSIONS: An ad libitum reduced-GL diet appears to be a promising alternative to a conventional diet in obese adolescents. Large-scale randomized controlled trials are needed to further evaluate the effectiveness of reduced-GL and -glycemic index diets in the treatment of obesity and prevention of type 2 diabetes.