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Measuring glycaemic responses: duplicate fasting samples or duplicate measures of one fasting sample?

Published online by Cambridge University Press:  08 March 2007

Thomas M. S. Wolever ,
Blanche Ip  and
Elham Moghaddam
Thomas M. S. Wolever*
Affiliation:
Department of Nutritional Sciences, University of Toronto, Toronto, Ontario, Canada M5S 3E2
Blanche Ip
Affiliation:
Department of Nutritional Sciences, University of Toronto, Toronto, Ontario, Canada M5S 3E2
Elham Moghaddam
Affiliation:
Department of Nutritional Sciences, University of Toronto, Toronto, Ontario, Canada M5S 3E2
*
*Corresponding author: Dr Thomas Wolever, fax +1 416 978 5882, email thomas.wolever@utoronto.ca
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Abstract

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The precision with which glycaemic responses, expressed as incremental area under the curve (AUC), can be measured may be improved by using the average of several measures of fasting blood glucose (FBG). To see if taking two fasting blood samples would increase the precision of AUC, the glycaemic responses elicited by four test meals (50 g glucose; 50 g glucose plus 10 g fat and 10 g protein; 100 g white bread; 100 g white bread plus 10 g fat and 10 g protein) were determined in thirteen overnight-fasted healthy subjects. Two fasting blood samples were taken 5 min apart (−5 min and 0 min before starting to eat) with glucose measured three times in each sample. AUC was calculated using different estimates of FBG derived from the three measures of glucose in the two fasting blood samples and each set of AUC values subjected to ANOVA. Unexpectedly, the results were more precise when AUC was calculated from mean glucose in the 0 min blood sample (FBG0) than from mean glucose in the two different fasting blood samples. The 95 % CI of the AUC calculated using FBG0 in thirteen subjects was ±29·8; to obtain the same CI using the mean of the two fasting blood samples would require fourteen subjects. These results suggest that taking two fasting blood samples does not necessarily improve, and may even reduce, the precision of AUC as a measure of glycaemic response. Further studies are needed before requiring that two fasting blood samples be taken for determining glycaemic index.

Keywords

Human glycaemic responsesCarbohydratesGlucoseGlycaemic indexMethodology
Type
Short Communication
Information
British Journal of Nutrition , Volume 96 , Issue 5 , November 2006 , pp. 799 - 802
Copyright
Copyright © The Nutrition Society 2006

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