Abstract
An official method for determining food glycemic index (GI) was published by the Organization for International Standardization (ISO) in 2010, but its performance has not been assessed. Therefore, we aimed to determine the intra- and inter-laboratory variation of food GI values measured using the 2010 ISO method. Three laboratories (Australia, Canada and France) determined the GI and insulinemic-index (II) of six foods in groups of 13–15 participants using the 2010 ISO method and intra- and inter-laboratory Standard Deviations (SDs) were calculated. Overall mean food GIs varied from 47 to 86 (p < 0.0001) with no significant difference among labs (p = 0.57) and no food × laboratory interaction (p = 0.20). Within-laboratory SD was similar among foods (range, 17.8–22.5; p = 0.49) but varied among laboratories (range 17.5–23.1; p = 0.047). Between-laboratory SD of mean food GI values ranged from 1.6 to 6.7 (mean, 5.1). Mean glucose and insulin responses varied among foods (p < 0.001) with insulin (p = 0.0037), but not glucose (p = 0.054), varying significantly among labs. Mean II varied among foods (p < 0.001) but not among labs (p = 0.94). In conclusion, we found that using the 2010 ISO method, the mean between-laboratory SD of GI was 5.1. This suggests that the ISO method is sufficiently precise to distinguish a mean GI = 55 from a mean GI ≥ 70 with 97–99% probability.
Highlights
The glycemic index (GI) was developed in 1981 as a way to classify carbohydrate-rich foods according to their postprandial glycemic impact [1]
Fasting glucose was significantly lower in Lab 2 than the other centers, which is likely due to the fact that Lab 2 measured whole blood glucose while the other centers measured plasma glucose (Table 2)
The results show that there was no significant difference in the mean GI of six foods covering a wide range of GI values measured using the International Standardization (ISO) method [8] among the three participating laboratories, and no significant food × laboratory interaction
Summary
The glycemic index (GI) was developed in 1981 as a way to classify carbohydrate-rich foods according to their postprandial glycemic impact [1]. Evidence is accumulating that GI is a marker of carbohydrate quality relevant to public health [2]. A strong case can be made that high GI diets are causally related to the development of type 2 diabetes [3,4]. There are many real and perceived barriers to the practical application of GI [5]; one real requirement is the need for an accurate and precise method for measuring GI. In 2005, the method was reviewed and updated [7], and in 2010, an official
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