I understand that the GI Index measures how quickly a substance releases carbohydrate. Why isn't the same structure applied to foods containing protein because protein does contain the same calories as carbs per gram and they can be used as an energy source?

The main reason is that meat does not contain carbohydrate and therefore does not raise the blood glucose level, so its effective glycemic index is zero. This doesn't mean that the calorie content isn't important. In following a diabetic diet it is still important to watch your portions.

 

Clarissa

Also, most meat is pretty similar to other meat in terms of protein structure.