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Glycemic Index and Glycemic Load
August 28, 2006
What’s this thing called the glycemic index? Is it a meal-planning method? Does it work? The glycemic index is a hot topic these days, it seems. But it’s a controversial topic, too. This week, I thought I’d try and shed some light on the glycemic index and hopefully clear up any misconceptions you may have.
The glycemic index (GI) has actually been around for about 20 years. Researchers at the University of Toronto came up with this tool back in the 1980’s. GI is really a ranking system of carbohydrate foods based on how they affect blood glucose levels. Carbohydrate foods are assigned a number between 0 and 100 based on that effect. Foods that have a GI of more than 70 are considered to be “high,” foods with a GI between 55 and 70 are “moderate,” and foods with a GI below 55 are “low.”
Why do foods have different GIs? Much of the reason has to do with how quickly the food breaks down during digestion, and therefore, how quickly blood glucose levels go up after eating. Let’s take a look at some foods and see how they’re classified:
You may be surprised to see that M&Ms have a low GI, while watermelon has a high GI. Does this mean that you should be eating M&Ms and not watermelon? Of course not. This is one of the flaws of the GI. The point is not to completely avoid high-GI foods and only eat low GI foods. Not only is that not practical, but it would mean forgoing many healthy foods that contain important nutrients. Also, many factors can affect the GI of a food, including the following:
Other factors can influence how a particular food affects blood glucose levels, too, such as the amount fat and fiber in it (both fat and fiber tend to slow the rise in blood glucose levels after a meal).
One other “downside” of the GI is that fact that the ranking system doesn’t take into account the amount of food one eats. Here’s an example. People are often surprised to see that carrots, much like watermelon, have a high GI. The inclination is to stop eating carrots. But think back to your nutrition class in school—carrots are good for you! Besides being low in calories, high in fiber, and rich in beta-carotene, a half-cup of carrots has just 8 grams of carbohydrate. So why does it have a high GI?
The GI was originally developed by researchers for research purposes, and it was calculated from servings of food that contained 50 grams of carbohydrate. In the case of carrots, you’d have to eat about 1 1/2 pounds to get that much carbohydrate! Would you eat that many carrots at one time? Probably not. The GI doesn’t take into account realistic serving sizes. However, the glycemic load does.
Glycemic load (GL) is the amount of carbohydrate in a food multiplied by that food’s GI. The GL is also a ranking of how foods affect blood glucose levels, but unlike GI, the GL takes serving size into account. Like GI, the lower the GL, the lower the spike in blood glucose levels. Low-GL foods have a value of 10 or less; moderate-GL foods have a value of 11-19; and high-GL foods have a value of 20 or more.
Back to the carrots, then. Carrots have a GI of 71. If we multiply the 8 grams of carb in a half cup by .71, we get a GL value of roughly 6. Therefore, carrots are a low-GL food. This means that, unless you truly are going to eat a pound and a half at a time, carrots don’t have a big impact on blood glucose levels.
The concepts of glycemic index and glycemic load can be overwhelming for some people, and may not be practical for everyone. Keep in mind that these are adjunct, or supplemental, meal planning tools to use if you’re already carb counting or following another meal planning method. You need to master the basics, first!
Is there a way to easily integrate the GI/GL into your day-to-day meal planning? Yes. Here are some suggestions to get you started:
For more information on glycemic index and glycemic load, check out the following Web sites:
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