Fast Carbs | Slow Carbs

The glycemic index helps keep your blood glucose in check and your life in balance

By Stephanie Thurrott
Illustration by Dave Granlund

All foods affect your blood sugar levels, but some cause sharper spikes than others. By keeping an eye on the glycemic index levels of the foods you eat, you may be able to keep your glucose levels more stable. Beth Anderson, RD, CDE, of Liberty Medical’s Diabetes Self-Management Program, answers some questions about how the glycemic index works.

What is the glycemic index?

The glycemic index of a food is defined as the increase over fasting blood glucose the food elicits two hours after it’s consumed. To arrive at the GI number, a constant amount of the food (usually a 50-gram carbohydrate portion) is divided by the response to a reference food (usually glucose or white bread). Pure glucose has a GI of 100, and other foods are rated in comparison to glucose. So a food like cornflakes, with a GI of 92, raises blood sugar levels almost as much as pure glucose, compared with All-Bran®, which has a GI of 51.

What do the numbers tell me?

Foods with a lower GI level don’t cause large changes in your glucose levels two hours after a meal, so they tend to be better choices, especially for people with diabetes. The ratings for foods fall into three categories:

Low: 55 or less Medium: 56 to 69 High: 70 or higher

The American Diabetes Association’s 2008 Clinical Practice Recommendations notes that “For individuals with diabetes, the use of the glycemic index and glycemic load may provide a modest additional benefit for glycemic control over that observed when total carbohydrate is considered alone.” That is, the GI can be used to help fine-tune glycemic control. Some people may benefit from low-GI foods, especially at breakfast, and others may not. Only by testing blood glucose levels before and after meals will people be able to determine whether some foods raise their glucose levels more than others.

People who eat a lot of foods high on the GI may be more prone to obesity, heart disease and diabetes.

Are foods with low glycemic index levels healthy?

The GI does not indicate the nutrient composition or quality of foods. Therefore, people should not necessarily be discouraged from eating foods that provide quality nutrients simply because they have a high glycemic index or glycemic load

Where do some typical foods fall on the index?

Generally, foods high in refined carbohydrates, like some breads, some potatoes, white rice and some lower-fiber cereals, have high GI levels. Some fruits, non-starchy vegetables, whole grains and legumes have lower GI levels, but there are exceptions. The chart on below lists the GI levels for lots of familiar foods.

What else can affect the glycemic index?

Foods aren’t usually eaten in isolation, so other foods you eat at the same time, fat and protein levels in the food, and how the food is prepared can affect how your body responds. Plus, no two foods are exactly alike, so the index assigned to them is an approximation. Don’t worry about differences of 5 or 10 points on the scale.

What makes foods have different GI levels?

Foods that have the same amounts of carbohydrates can have very different GI levels depending on the variety (such as long-grain and short-grain rice), how much they are processed, how ripe they are and how big their particles are. For example, diced potatoes may have a higher GI than a whole potato. Fiber will make a difference too. A sweet potato will have a lower GI than a white potato because the fiber content in a sweet potato is higher. Also, the amount of fat consumed in a meal can slow down glycemic response.

You mentioned the term “glycemic load” in the ADA’s recommendations. How does that compare to the GI?

The glycemic index is based on 50 grams of carbohydrates in a food. For some foods, you would have to eat a lot to equal that many carbs. The glycemic load takes serving size into account and attempts to incorporate both the quality and the quantity of carbohydrate consumed.

One way to incorporate the glycemic index into your diet is to exchange one higher-GI food for a lower-GI food at each meal, and if you are testing your blood glucose levels before and after meals, you will be able to see whether this change is helping to control your blood sugar.
HM

† Meter offer available to qualified beneficiaries with diabetes. Not available to current Liberty patients. No purchase necessary. Meter shown for illustrative purposes only. Meter offer not applicable to all brands of meter. Commemorative keychain offer and free HealthMatters subscription dependent on patient enrollment. Combined offer available while supplies last. Terms and conditions apply.

* Up to 90 days from shipment (a longer period may apply based on law or regulation). Some restrictions apply. We are unable to accept returns of properly filled prescriptions.