Maybe this is getting into the weeds a bit on the science/chemistry of how our bodies digest, but it has never made sense to me that some complex carbs (polysaccharides) like rice, breakfast cereals, white bread can have a higher glycemic index than sucrose, a disaccharide? Sucrose has a GI of 65, whereas rice is 72, white bread is 71, and corn flakes are 77. I understand that the “processed” nature contributes to it, but shouldn’t these still be more, well, complex than table sugar??
A significant downfall to glycemic index is that it doesn’t account for serving size. As a result, glycemic index can sometimes have some weird implications.
A great example of this is watermelon - considered a high glycemic index food (76 - roughly on par with a doughnut, purely due to the amount of carbohydrate in the watermelon. However, 1 cup of watermelon (standard fruit serving) contains roughly half the amount of carbs as a medium doughnut. So despite the fact that they have the same index, it would take roughly twice as much watermelon to have the same actual impact on glucose.
This is where glycemic load comes into play. It is functionally the index with serving size taken into account.
Table sugar is composed by glucose and fructose, the latter of which does not cause any glycemic response in the blood - which is why table sugar is pretty much halfway across the index. Any source of carbohydrates with a higher proportion of other saccharides with respect to fructose can score higher on the index