British Journal of Nutrition

Short Communication

Effect of coffee and tea on the glycaemic index of foods: no effect on mean but reduced variability

Ahmed Aldughpassia1 and Thomas M. S. Wolevera1 c1

a1 Department of Nutritional Sciences, University of Toronto, Toronto, Ontario, Canada M5S 3E2


Coffee and tea may influence glycaemic responses but it is not clear whether they affect the glycaemic index (GI) value of foods. Therefore, to see if coffee and tea affected the mean and sem of GI values, the GI of fruit leather (FL) and cheese puffs (CP) were determined twice in ten subjects using the FAO/WHO protocol with white bread as the reference food. In one series subjects chose to drink 250 ml of either coffee or tea with all test meals, while in the other series they drank 250 ml water. The tests for both series were conducted as a single experiment with the order of all tests being randomised. Coffee and tea increased the overall mean peak blood glucose increment compared with water by 0·25 (sem 0·09) mmol/l (P = 0·02), but did not significantly affect the incremental area under the glucose response curve. Mean GI values were not affected by coffee or tea but the sem was reduced by about 30 % (FL: 31 (sem 4) v. 35 (sem 7) and CP: 76 (sem 6) v. 75 (sem 8) for coffee or tea v. water, respectively). The error mean square term from the ANOVA of the GI values was significantly smaller for coffee or tea v. water (F(18, 18) = 2·31; P = 0·04). We conclude that drinking coffee or tea with test meals does not affect the mean GI value obtained, but may reduce variability and, hence, improve precision.

(Received April 21 2008)

(Revised August 19 2008)

(Accepted August 26 2008)

(Online publication September 25 2008)


c1 Corresponding author: Dr Thomas M. S. Wolever, fax +1 416 978 5882, email


Abbreviations: AUC, area under the curve; CP, cheese puffs; FL, fruit leather; GI, glycaemic index; WB, white bread