Abstract 4170: Inter- and Intra-Individual Variability in Glycemic Index Values for White Bread Determined Using Standardized Procedures
Glycemic index (GI) values are used to classify carbohydrate-containing foods on the basis of serum glucose response relative to a glucose challenge, and both the GI and glycemic load (GL) values (GI adjusted for total carbohydrate) of diets have been used to estimate chronic disease risk. There is an underlying assumption that GI values for a given food are highly reproducible for an individual and similar among individuals. To test this hypothesis the inter- and intra-individual variability of GI values for white bread were assessed in twenty-three healthy adults (20–70 y) under controlled conditions using up to three sets of two challenges, white bread and glucose, administered in random order. Using the published standard protocol, the GI value was calculated by dividing the 2-h incremental area under the serum glucose response curve (AUC) for 50 g available carbohydrates from commercial white bread by the AUC for 50 g glucose. The mean GI value of the first set was 78 ± 73 (N=23), with an inter-individual coefficient of variation of 94%. The intra-individual reproducibility of the GI value for those subjects who completed three sets (n=14) was calculated using individual AUC values for white bread divided by the mean of the three AUC values after glucose, and were 78 ± 39, 60 ± 17 and 75 ± 37 for tests 1, 2 and 3, respectively. Inter-individual coefficients of variation were 50%, 29% and 50%, respectively. The mean GI value of these three sets was 71 ± 22, with an intra-individual coefficient of variation of 30%. These data suggest that despite the reduction in inter- and intra-individual variability with replicate testing, individual responses to a single food, white bread, are highly variable. Caution should be used in drawing conclusions on the basis of GI or GL values until there is a better understanding of inter- and intra-individual variability in response to individual foods and food mixtures.