Choosing food: Glycemic Index vs. Glycemic Load

If you are watching your carbs, whether trying to control your blood sugar or because you are on a low-carb diet, you have no doubt heard the terms "Glycemic Index" and "Glycemic Load" getting thrown around a lot.

Historically, Glycemic Index (GI) was the first one to come along. This is the metric by which most of the older low-carb diets (including Atkins) measure their food recommendations. The Glycemic Index is why the Atkins diet allows broccoli but not carrots. Broccoli has a GI under 20, while a carrot's GI is in the "High" category, over 60 - it's up there with starchy foods like corn and potatoes.

If you are skeptical that a carrot can have the same impact on your blood sugar as Skittles or a Mars Bar… you're right. Although the GI is what we used for many years, it has since been supplanted by Glycemic Load.

Glycemic Load basically takes the GI of a food, then refactors it based on serving size.

For example, both carrots and Skittles contain carbs. However, you would have to eat 4.25 cups of carrots in order to get the same amount of carbs as in one small 2oz bag of Skittles. Looking back, I don't know why the Glycemic Index never thought to take serving size into account. It seems pretty obvious in hindsight that the Glycemic Index, although a useful lab tool, is not a realistic way to structure a diet.

Also, unlike the Glycemic Index, Glycemic Load takes into account the amount of the food you eat. This makes sense, because the more Skittles you eat at once, the higher your blood sugar will spike. One cup of Skittles has a Glycemic Load of 132 (!!) whereas a 20-gram Fun Size package has a Glycemic Load of only 13.

Image courtesy Flickr/Fovea Centralis