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.