Determination of glycaemic index; some methodological aspects related to the analysis of carbohydrate load and characteristics of the previous evening meal

Objectives: To determine the possible differences in glycaemic index (GI) depending on ( 1) the analytical method used to calculate the 'available carbohydrate' load, that is, using carbohydrates by difference ( total carbohydrate by difference, minus dietary fibre (DF)) as available carbohydrates vs available starch basis ( total starch minus resistant starch (RS)) of a food rich in intrinsic RS and ( 2) the effect of GI characteristics and/or the content of indigestible carbohydrates ( RS and DF) of the evening meal prior to GI testing the following morning. Design: Blood glucose and serum insulin responses were studied after subjects consuming ( 1) two levels of barley kernels rich in intrinsic RS (15.2%, total starch basis) and ( 2) after a standard breakfast following three different evening meals varying in GI and/or indigestible carbohydrates: pasta, barley kernels and white wheat bread, respectively. Subjects: Healthy adults with normal body mass index. Results: ( 1) Increasing the portion size of barley kernels from 79.6 g ( 50 g ` available carbohydrates') to 93.9 g ( 50 g available starch) to adjust for its RS content did not significantly affect the GI or insulin index (II). ( 2) The low GI barley evening meal, as opposed to white wheat bread and pasta evening meals, reduced the postprandial glycaemic and insulinaemic ( 23 and 29%, respectively, P