Jan 29, 2015

The Glycemic Index

In the world of popular diets, the glycemic index (GI) is hot. Low carb eating plans tout the benefits of low glycemic foods over high glycemic ones, and there are even entire diets based on eating low GI meals.

By Dr. Christopher Mohr

Christopher Mohr, PhD, RD, is the President of Louisville, Ky.-based Mohr Results, Inc., which provides nutrition and training consultations for individuals and corporations. He can be reached through his Web site: www.MohrResults.com.

The glycemic index is important for athletes, too, but in a much different way. Athletes should not avoid high glycemic foods. However, they should know when to eat high and low GI foods to enhance performance. In this article, I’ll explain how the glycemic index relates to nutrition for athletes.

What is the Glycemic Index? The first thing to understand is that all carbohydrates are not created equal. People often lump carbohydrates together as one whole category without any distinction, but carbs are a diverse group. For example, a slice of packaged white bread is very different from an apple.

This inequality is partly because of the varied nutrient content of different foods. But it also has to do with how the food is digested and utilized by the body—and this is what the glycemic index is all about. Plant-based carbohydrates are high in fiber, slowing the digestion and absorption rate, and have a low glycemic index. Sweet foods, such as soft drinks, candy, and sugar coated cereals, are stripped of most nutritional benefits, so they are absorbed more rapidly. They are high on the glycemic index scale.

Very simply, the glycemic index is a ranking of carbohydrates based on their immediate effect on blood glucose (blood sugar) levels. The blood glucose response is called the glycemic response, and is determined by ingesting a food containing 50 g of carbohydrate and comparing it over a two-hour period to a “standard” carbohydrate. White bread is typically used for the “standard” carbohydrate, and its assigned value is 100. Thus, a food with a glycemic index of 60 will raise blood glucose 60 percent as much as would an equal amount of white bread.

The classification of high, moderate, and low glycemic index foods varies from source to source, but the most common ratings are:

High: over 70

Moderate: 56 to 69

Low: under 56

Should athletes focus on it? The glycemic index can be a useful tool for athletes for two reasons. First, athletes can use GI to make sure they are eating a healthful diet. As a rule of thumb, athletes should focus on eating low and moderate glycemic foods, which are higher in fiber, vitamins, and minerals than high glycemic foods. Good choices include whole grains, most fruits, and many vegetables.

High glycemic foods contain refined carbohydrates and tend to be less nutritious. They include sweetened cereals, white bread, candy, and rice.

However, when it comes to what athletes should consume during and after events or practices, high glycemic foods are the best choice. This is the second important GI fact to remember. Because high glycemic foods are low in fiber and digest quickly, they speed glycogen replenishment, and subsequently aid the recovery process. That’s why sports drinks and easily digested foods are recommended post-practice.

Words of warning. There are definitely benefits to using the glycemic index. However, there are also some caveats. For example, watermelon and carrots have a high glycemic index, and thus many popular fad diets say to limit or eliminate them. But these foods are rich in nutrients, and are great choices for athletes.

In addition, many high glycemic foods are not eaten alone. Most people won’t sit down and have several slices of bread without anything else. When cold cuts, butter, or olive oil are combined with bread, for example, the glycemic index of the meal changes because fat, protein, and fiber all slow absorption. Non-carbohydrates tend to have a very low glycemic response.

As with most issues in nutrition, the glycemic index is not cut and dry. Athletes need to be savvy about how it relates to their needs, and also understand how it affects performance. They need to forget the advice of popular diets, and learn how the right foods at the right times can help them succeed.

Table: GI Values of Some Common Foods

Note: GI values may vary slightly from source to source. Additional information and more extensive lists can be found at: www.glycemicindex.com