Old Vs New Glycemic Index

Comparisons and Issues

glycemic index chart

If you seem to remember a glycemic index that had some foods with values over 100, you aren’t hallucinating. For quite awhile there were two coexisting glycemic indexes. The other one was based on white bread, rather than glucose. In that one, white bread had a glycemic index of 100, and there were quite a few foods that were higher than 100, including potatoes, rice cakes, and some breads and cereals.

On that scale, glucose had a value of 143.

The white bread index how now fallen out of favor, making glucose the standard. This makes intuitive sense, since 1) it is, after all, glucose in the blood that is being measured, 2) any glucose ingested goes to the blood extremely quickly, and 3) glucose is the same the world over, whereas “bread” is quite variable.

What We Are Losing with The New Index

The main negative with the glucose-based index is that it magnifies some of the problems inherent in the index itself. To simplify, there is are two issues:

1) There is a great deal of variability in how much a food affects people's blood glucose  - so much so that it can be misleading to condense it into a single number.  For example, you can see in this food list that the glycemic response to something as straightforward as honey varied from 32 to 87 in testing.  32 is considered to be a low glycemic index, and 87 is considered to be high, but honey is generally given the label of medium because the average is 55.

You can imagine that there is a potential for even more variability when the foods are more complex, like, for example, a muffin or a pancake, both of which appear in glycemic index lists.  Differences in recipes, cooking processes types of ingredients are all going to make a difference, as the glycemic index is compiled from studies done on foods around the world.

  This also probably accounts for sometimes large differences in foods such as fruit, as the differences between varieties can be large.

2) Almost all foods are "medium" on the glycemic index,  When you rule out the high and low foods there are a whole bunch in the middle with very similar scores. (More detail on this) The problem is that when you reduce the range by making the upper end 100 instead of 143, you make the problem even worse. Now the numbers are not just close to each other, they are practically the same, so it's even more difficult to differentiate between foods. When you have a broader range of numbers to play with, the difference between foods (if there really is one) becomes clearer.

It seems to me it's likely that these reasons have something to do with studies coming how that the glycemic index doesn't matter.  The index itself may make it less likely that a study will get significant results, even if there is a true difference between foods. This would especially be true for studies which divide people into low, medium, and high glycemic diets.

Almost by definition you aren’t going to have many people eating low glycemic diets unless the diet is also low in carbs.

Glycemic Index Food Lists

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