Abstract 569 Endocrinology & Diabetes III Platform, Sunday, 5/2

Background and purpose of study: The increasing incidence of obesity and NIDDM in the American population has lead to recommendations to reduce the fat intake. To maintain energy balance, such recommendations imply a corresponding increase in carbohydrate (CHO) intake. The present studies were undertaken to determine if a diet high in CHO and low in fat content (HC) has an impact on glucose homeostasis in adolescents.

Subjects: Ten adolescents (6 boys; 4 girls) (Age 14.5±0.4 y; Weight 57.4±3.4 kg; Height 165.9±2.4 cm; % body fat (DXA) 15.9±1.7; Tanner stage IV-V) were studied in the postabsorptive overnight fasting condition at two occasions preceded by 7 days of a diet containing either 60% CHO, 25 % fat and 15% protein (HC), or 30 % CHO, 55 % fat and 15% protein (LC).

Methods: Pre-packed meals were delivered daily and unconsumed food was returned and analyzed. Total energy expenditure (EE) and CHO, fat and protein oxidation in response to the two diets were analyzed over 24 hrs in a room calorimeter. GPR was measured by isotope dilution using [1-13C]glucose and GNG from the 2H enrichment at C6 of glucose following intake of 2H2O. The data obtained at the two study occasions were compared by paired t-test.

Results: CHO oxidation was (mean±SE) 52±3% and fat oxidation 31±3% on the HC diet, and appropriately changed to 34±21 and 51±2%, respectively, on the LC diet. Plasma glucose concentration was 4.8±0.1 (HC) and 4.9±0.1 mM (LC)(NS); plasma insulin was 8.2±0.9 (HC) and 6.3±0.7(LC) µU/mL (p<0.05); C-peptide 1.7±0.2(HC) vs 1.5±0.2(LC) ng/mL (NS); GPR was 12.8±0.5(HC) and 12.0±0.4(LC) µmol/kg min (p<0.01), GNG rate was 7.0±0.4 (HC) vs 7.0±0.3 (LC) µmol/kg min(NS) and the fraction of GPR derived from GNG was 55±3 (HC) vs 58±2 (LC) % (NS).

Conclusion: Except for slight declines in GPR and insulin concentration on the LC diet, other parameters of glucose metabolism were not affected by CHO intakes in the range of 30-60 % of the dietary energy intake. The expected higher CHO oxidation on the HC (low fat) diet and the higher fat oxidation on the LC (high fat) diet implies that at least in the short-term, healthy adolescents adapt to extreme changes of the dietary carbohydrate and fat intake by appropriately adjusting the substrate oxidation rates.