the glycemic index

The latest buzz in the world of nutrition is the glycemic index (GI). You’ll see the GI recommended for use in weight loss, disease prevention, and optimal exercise performance.

Glycemic index began as a desire to understand how foods impact blood sugar, to help diabetics achieve better blood sugar control. A specific amount of carbohydrate (50 grams) is eaten, and the blood sugar response is measured. Different foods contain different amounts of carbohydrate, so the amount that has to be eaten (to get 50 grams of carb) will be unique for each food. The GI is calculated by comparing the blood sugar response provoked by a particular food to the same carbohydrate dose in a reference food, either pure glucose or white bread.

Recent research suggests that there may be benefits to eating a low GI diet, in other words, one that doesn’t impact blood sugar too much. But there are a few things you should know about the GI before you go out and stock your pantry with low glycemic index crackers, cereals, and granola bars.

1. The GI is derived from a response to food, but it is not a universal quality of that particular food. Two people may respond differently to the same food, based on other qualities of that food.

2. Glycemic index classifications are arbitrarily assigned. It was decided that a low glycemic index is considered less than 55, medium values are 55-70, and high values are greater than 70. The reference food is set at a value of 100.

3. Glycemic index doesn’t describe the nutrient density of a food. A candy bar has a lower GI than a banana, but the banana provides more nutrients.

4. Glycemic index is affected by the time of day a food is eaten and by the meal. The GI of a food tends to be different later in the day after the first meal is eaten.

5. Many other factors can affect the GI of a food, such as whether it is mashed or ground, cooked or cooled, where it was grown, and ripeness.

6. Glycemic index tests a single food. Foods are usually eaten in combinations and tend to have a lower GI than when eaten alone.

There are many limitations to the glycemic index. It doesn’t seem prudent to avoid potatoes, carrots, bread, or bananas because they have a higher GI. What does make sense is to balance your foods, eating them in combination with other foods. Always keep the nutrient quality of foods in mind. Obviously, choose the banana over the candy bar.

More research needs to be done to truly understand the usefulness of the glycemic index. For now, don’t be seduced into buying a food simply because it is marketed as having a low glycemic index. And don’t be lured into diet plans that depend only on the glycemic index.

ABOUT THE AUTHOR: Carol Plotkin, MS, RD, is a registered dietitian. She is owner of ON NUTRITION, a nutrition practice specializing in wellness/disease prevention and sports nutrition. To find out more about her services, go to www.rochesternutrition.com. Contact her at cplotkin@rochesternutrition.com.