Author
VEGA-LOPEZ, SONIA - TUFTS/HNRCA | |
AUSMAN, LYNNE - TUFTS/HNRCA | |
GRIFFITH, JOHN - TUFTS UNIVERSITY | |
Lichtenstein, Alice |
Submitted to: Diabetes Care
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/15/2007 Publication Date: 3/23/2007 Citation: Vega-Lopez, S., Ausman, L.M., Griffith, J.L., Lichtenstein, A.H. 2007. Inter- and Intra-Individual Variability in Glycemic Index Values for White Bread Determined Using Standardized Procedures. Diabetes Care. 30: 1412-1417. Interpretive Summary: Glycemic index (GI) values are used to classify carbohydrate-containing foods based on the extent to which they raise sugar in the blood. It is assumed that GI values for a given food are highly reproducible for an individual and similar among individuals. This study was conducted to evaluate the variability of the GI value within and among individuals when determined under strictly controlled conditions. Twenty-three healthy adults participated in the study and consumed 50 g available carbohydrates from commercial white bread and glucose, on different days. The GI value of white bread was calculated using the response to glucose as reference. The average GI value for white bread was 78 +/- 73, which is close to the reported value (70). However, the values obtained in different volunteers varied by 94%. Fourteen volunteers repeated the test on three occasions. The average GI value for white bread of these three sets was 71 +/- 22. There was a 30% variability in response when the GI of bread was measured in the same volunteer on different occasions. These data suggest that the glucose responses to a single food are highly variable between and within individuals. Technical Abstract: This study was conducted to evaluate the inter- and intra-individual variability of the GI value when determined under strictly controlled conditions. 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. The GI value was calculated by dividing the 2-h incremental area under the serum glucose response curve (AUC) for commercial white bread by the AUC for glucose. The mean GI value of the first set of determinations was 78 +/- 73 (N=23; mean +/- SD), with an inter-individual coefficient of variation (CV) of 94%. The intra-individual reproducibility of the GI value for a subset of participants who completed three sets (n=14) was calculated using each 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 CVs were 50%, 28% and 50%, respectively. The mean GI value of these three sets was 71 +/- 22 (mean +/- SD), with an intra-individual CV of 30%. These data suggest that despite a reduction in inter- and intra-individual variability with replicate testing, glycemic responses to a single food, white bread, are highly variable. |