Effect of glycemic index on whole-body substrate oxidation in obese women.
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.


METHODS
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).


CONCLUSIONS
This study demonstrates that dietary glycemic characteristics were unable to modify fuel partitioning in sedentary obese women.
Díaz
E O
EO
Laboratorio 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
Galgani
J E
JE
Aguirre
C A
CA
Atwater
I J
IJ
Burrows
R
R
D000328:Adult; D019540:Area Under Curve; D001786:Blood Glucose / Q000032:analysis; D002153:Calorimetry, Indirect; D018592:Cross-Over Studies; D004040:Dietary Carbohydrates / Q000378:metabolism*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D005934:Glucagon / Q000097:blood; D038321:Glycemic Index; D006801:Humans; D007328:Insulin / Q000097:blood; D009765:Obesity / Q000378:metabolism*; D010084:Oxidation-Reduction; D019518:Postprandial Period
D001786:Blood Glucose; D004040:Dietary Carbohydrates; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D005934:Glucagon