A randomized controlled trial to investigate the impact of a low glycemic index (GI) diet on body mass index in obese adolescents

BACKGROUND: The role of a low glycemic index (GI) diet in the management of adolescent obesity remains controversial. In this study, we aim to evaluate the impact of low GI diet versus a conventional Chinese diet on the body mass index (BMI) and other obesity indices of obese adolescents. METHODS: Obese adolescents aged 15–18 years were identified from population-recruited, territory-wide surveys. Obesity was defined as BMI ≥95th percentile of Hong Kong local age- and sex-specific references. Eligible subjects were randomized to either an intervention with low GI diet (consisting of 45-50% carbohydrate, 30-35% fat and 15-20% protein) or conventional Chinese diet as control (consisting of 55-60% carbohydrate, 25-30% fat and 10-15% protein). We used random intercept mixed effects model to compare the differential changes across the time points from baseline to month 6 between the 2 groups. RESULTS: 104 obese adolescents were recruited (52 in low GI group and 52 in control group; 43.3% boys). Mean age was 16.7 ± 1.0 years and 16.8 ±1.0 years in low GI and control group respectively. 58.7% subjects completed the study at 6 months (65.4% in low GI group and 51.9% in control group). After adjustment for age and sex, subjects in the low GI group had a significantly greater reduction in obesity indices including BMI, body weight and waist circumference (WC) compared to subjects in the control group (all p <0.05). After further adjustment for physical activity levels, WC was found to be significantly lower in the low GI group compared to the conventional group (p = 0.018). CONCLUSION: Low GI diet in the context of a comprehensive lifestyle modification program may be an alternative to conventional diet in the management of obese adolescents. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov Ref. No: NCT01278563