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Effect of glycemic index on whole-body substrate oxidation in obese women
E O Díaz1, J E Galgani, C A Aguirre
1Laboratorio de Metabolismo Energético e Isótopos Estables, Instituto de Nutrición y Tecnología de los Alimentos (INTA), Universidad de Chile, AV JP Alessandri 5540, Santiago, Chile. edaiz@uec.inta.uchile.cl
Background:
Glycemic index is hypothesized to determine fuel partitioning through serum plasma insulin modifications induced by dietary carbohydrates, thereby modulating fat accretion or oxidation.
Objective:
To assess the glycemic effects on postprandial fuel oxidation and blood response.
Design:
In all, 12 obese women were fed on a randomized crossover design with two test meals (breakfast+lunch). High- or low-glycemic meals were provided on separate days. Energy intake on high-glycemic meal was 7758+/-148 kJ and for low-glycemic meal was 7806+/-179 kJ. Carbohydrates supplied were 273+/-5 and 275+/-6 g, respectively. Macronutrient distribution was 55% carbohydrates, 30% fat and 15% protein. Fuel oxidation was measured continuously in a respiratory chamber for 10 h. Serum glucose, free fatty acids (FFA), insulin and glucagon samples were taken for 5 h after breakfast.
Results:
Glucose AUC changed significantly in response to different glycemic breakfast. Low- vs high-glycemic breakfast was 211+/-84 and 379+/-164 mmol/l (P<0.05). Similarly, insulin changed from 94+/-37 and 170+/-87 nmol/l (P<0.05), respectively. The rate of increment for serum glucose and insulin reached by the high- vs low-glycemic meal was 1.8 times more with the high-glycemic breakfast. Serum FFA were similarly suppressed by both meal types by 3 h after meal intake, but then raised significantly more with the low-glycemic meal by the fourth and fifth hour (P<0.05). Plasma glucagon did not show a significant variation with glycemic index. Carbohydrate and fat oxidation was not modified by glycemic meal characteristics, being virtually the same for low- vs high-glycemic comparisons in the 5 h following breakfast and lunch (P=NS).
Conclusion:
This study demonstrates that dietary glycemic characteristics were unable to modify fuel partitioning in sedentary obese women.
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