The glycemic index is often criticised for being complicated. Mostly because your blood sugar responds differently to the same food depending on whether it’s ripe, unripe, cooked, uncooked etc., but also because it underestimates the problems with pure sugar (fructose).
However, a great aspect of GI is how it shows that choosing whole-grain bread is not necessarily much better than white bread:
The glycemic index is “incredibly powerful” conceptually, added Dariush Mozaffarian, dean of the Friedman School and Jean Mayer Professor of Nutrition and Medicine. That’s because it highlights the fact that starch “is a hidden sugar,” he said. “If you don’t think about how rapidly starch and sugar in the foods that you are eating are digested, you are going to make incorrect eating decisions.”