Inter-Individual Variability and Intra-Individual Reproducibility of Glycemic Index Values for Commercial White Bread

Abstract

Objective: To assess the inter- and intra-individual variability of GI value determinations for white bread using glucose as the reference food.

Research design and methods: Twenty-three healthy adults (20-70 y) completed up to three sets of two visits per set. Each pair of visits assessed the glycemic response to 50 g available carbohydrates from commercial white bread and glucose, administered in random order. GI values were calculated by dividing the 2-h incremental area under the serum glucose response curve (AUC) after each commercial white bread challenge by the mean AUC for glucose.

Results: The mean ratio of the AUC after white bread intake by the AUC after glucose intake for the first set of determinations was 78±15 (mean±SEM; N=23; CV=94%). When using GI values calculated with the subset of participants who completed three sets of tests (n=14), GI values for each of the three sets of determinations were 78±10, 60±5 and 75±10 (mean±SEM), respectively. Coefficients of variation (CV) were 50%, 28% and 50%, respectively. The mean GI value of these three sets was 71±6 (mean±SEM), with a CV of 30%. When an analysis of variance approach was applied to these data the inter-individual coefficient of variation was 17.8% and the intra-individual variation was 42.8%.

Conclusions: These data suggest that in response to a challenge of white bread relative to glucose, within-individual variability is a greater contributor to overall variability than among-individual variability. Further understanding all the sources of variability would be helpful in better defining the utility of GI values.