The Glycemic Load

Every single time I think I have this nutrition thing wrapped up, another subject pops up - it's like peeling back the layers of an onion. Anyway, I need to explain Glycemic Load before I can continue with further discussions about the application of the Harvard Healthy Eating Pyramid.

The Glycemic Load (GL) is a refinement of the Glycemic Index (GI). I found a pretty good discussion of the glycemic index/load in the June 2001 issue of Harvard Women's Health Watch. I will paraphrase a rather lengthy article to get to the crux of the matter in a shorter period of time...

The Glycemic Index measures how fast and how far blood sugar rises after eating specific carbohydrates. So, in general, foods high on the Glycemic Index will raise blood sugar very quickly, lead to glucose spikes and crashes as I mentioned here, which can cause hunger (even immediately after a meal), leading to overeating. So any diet should attempt to avoid high GI foods as much as possible.

The problem is, the Glycemic Index is based on 50 grams of the specific carbohydrate; however, a serving of a food may have nowhere near 50 grams of carbohydrate. In an effort to refine the glycemic effect of a standard serving of a specific food, a formula for Glycemic Load (GL) was derived to take into account the actual amount of carbohyrate in a serving: Glymeic Load = "Glycemic Index" x "carbohydrate in one serving" / 100.

Take for example, watermelon and baked potato:

• watermelon: GI = 72 (high), but GL = 4.32 (low), since a serving has only 6 grams of carbohydrate
  
• baked potato: GI = 85 (high), and GL = 25.5 (high), since there are 30 gm of carbohydrates in a potato

This Australian site will calculate Glycemic Load for a wide range of foods and brands, and also has a good FAQ on all things glycemic.

It was difficult to find what constituted high and low Glycemic Loads because all I was able to find were commercial sites such as this one, but I am now confident that a GL of 10 or less is low and a GL of 20 or more is high. These values correspond to a GI of 55 or less being low, and a GI of 70 or more being high. Together, GI and GL should allow you to refine your diet plan to exclude those carbohydrates and foods that will cause glucose spikes and crashes.