There’s an interesting look at the use of Glycemic Index and Glycemic Load as a means for diabetics to control blood sugar (Estimating the reliability of glycemic index values and potential sources of methodological and biological variability. Nirupa R Matthan Lynne M Ausman Huicui Meng Hocine Tighiouart Alice H Lichtenstein. The American Journal of Clinical Nutrition, Volume 104, Issue 4, 1 . October 2016, Pages 1004–1013).
These data indicate that there is substantial variability in individual responses to GI value determinations, demonstrating that it is unlikely to be a good approach to guiding food choices. Additionally, even in healthy individuals, glycemic status significantly contributes to the variability in GI value estimates.
Here’s where I think there’s a point but it may not be relevant. Sure the numbers are not absolute for all individuals. It shouldn’t be a surprise to anyone that some people are more tolerant of carbohydrates than others. In fact, that’s part of the very reason that Low Carb works so well for those of us that are more sensitive to carbohydrates than others.
I have no doubt that the area under the curve for my blood sugar response when I was a diabetic was much higher than most healthy people. That explains some of the variability. However, this study used subjects who were all pretty healthy. Interestingly, the HbA1C average of this group was between 5.5% and 5.6% with a range plus/minus 0.5%. Some of these may be pre-diabetic and unaware of it.
What would be more interesting than person to person variability in the absolute value of the GI number would be the relative numbers for each of the groups.
Variability – Width of the Standard Deviation
There was a pretty wide standard deviation in the number reported:
The mean ± Standard Deviation (SD) Glycemic Index (GI) value for white bread was 62 ± 15 when calculated by using the recommended method.
Yes, that’s around 25% variability which is fairly wide. As the study stated:
… we documented substantial variability in the mean intra-individual (20%) and inter-individual (25%) CVs for a single food, white bread.
So not only were differences noted in the values between different people but even the same person had different responses to the same load.
Here’s the 2002 Standard table for GI/GL (International table of glycemic index and glycemic load values: 2002. Kaye Foster-Powell, Susanna HA Holt, and Janette C Brand-Miller).
Here’s a shorter table listing the GI for various foods (Glycemic Index Chart: GI Ratings for Hundreds of Foods). Foods listed as “Low Glycemic Index” as not necessarily low carb. For instance, broccoli (GI=15) and cranberries (GI=45) are both Low Glycemic Index since they are less than GI=55 but there’s three times the GI represented in cranberries compared to broccoli.
The American Diabetics Association states (Glycemic Index and Diabetes):
Studies also show that the total amount of carbohydrate in food, in general, is a stronger predictor of blood glucose response than the GI.
… for most people with diabetes, the first tool for managing blood glucose is some type of carbohydrate counting.
Because the type of carbohydrate can affect blood glucose, using the GI may be helpful in “fine-tuning” blood glucose management. In other words, combined with carbohydrate counting, it may provide an additional benefit for achieving blood glucose goals for individuals who can and want to put extra effort into monitoring their food choices
Good points. But why not mention just limiting carbohydrates altogether?