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Glycemic Index and Glycemic Load

The Glycemic IndexYou may have heard the terms glycemic index or glycemic load being mentioned when your doctors discuss nutrition and health. They are helpful dietary concepts, but they’re only helpful if we understand them and, frankly, most of us don’t! Let’s get down to basics.

The Glycemic Index (GI)

The Glycemic Index (GI) is used to classify foods based on how quickly they cause a rise in blood sugar (also called glucose) upon being eaten. The GI separates foods into three general categories:
  • High GI: 70 and above
  • Medium GI: 55-69
  • Low GI: 54 or less
Sugar and white bread are considered reference foods and have been assigned a GI=100 because they both cause a rapid rise in blood sugar levels after ingestion. All other foods are assigned a lower value from 1-99 based on how they affect blood sugar when eaten relative to sugar or white bread.

When high GI foods are eaten, a rapid rise in blood sugar occurs followed by a significant release of insulin. Recall that insulin removes glucose from the blood, delivering it to cells of the body where it is used for energy, so blood sugar levels fall. This, in turn, leads to fatigue and hunger, as well as undue stress on your body. Consistently eating high GI foods may lessen your body’s sensitivity to insulin over time, leading to type 2 diabetes and other illnesses.

Foods with a lower GI are digested more slowly, resulting in a more gentle rise in blood sugar followed by a more moderate release of insulin, thereby helping to maintain consistent blood glucose levels, lessen fatigue, and reduce hunger.

Consider the GI a helpful guide when choosing healthy carbohydrates. The general idea is to lessen your intake of high GI foods. The easiest ways to do that? Go “less white” (eat less white bread, white sugar, white potatoes, anything made with white flour), limit sugary drinks and desserts, and highly processed foods.

Glycemic Load (GL)

Glycemic Load (GL) takes the concept of GI a step further, accounting not only for how rapidly an ingested food causes a rise in blood sugar, but also the relative amounts of carbohydrate the food contains in an average serving. Thus, the GL offers a more accurate reflection of the impact eating specific foods has on your blood sugar and insulin levels.

Foods are ranked by Glycemic Load using the following scale:
  • High GL: 20 or above
  • Medium GL: 11-19
  • Low GL: 0-10
Watermelon and BagelsSome foods with a high GI actually have a low GL. Let’s take watermelon as an example – it has a GI of 72 (pretty high!), but since it’s mostly made up of water and actually contains relatively little carbohydrate, it’s GL is only between 4-7 (pretty low!). Thus, your blood sugar may go up rapidly after eating watermelon, but it shouldn’t go up very much, since there’s not much carbohydrate present in watermelon to be converted into sugar in the first place. On the other hand, ½ a bagel has a GI similar to watermelon (72), but a much higher GL of almost 26 (so a bigger sugar load).

More Tips for Achieving Low Glycemic Eating:
  • Eat high GI/GL foods in small portions combined with high fiber foods, and maybe a little protein or fat
  • Add a little lemon juice or vinegar to your recipes (acidity slows the movement of food through the stomach, slowing digestion and thus absorption of sugar)
  • Prepare your pasta al dente (avoid “gooey” or sticky starches)
There are many reference lists you can refer to find out more about the GI or GL of the foods you enjoy. For example, allows you to look up both the GI and GL of any food in their database for free.

Please keep in mind that even though both the GI and GL offer some insight into how specific foods affect your blood sugar, you cannot determine whether or not those foods are healthy for you based solely on these numbers - diet books making this claim are misleading. GI and GL are useful concepts that can help guide your choice of carbohydrates to eat, but the quality and concentration of nutrients found within a given food have to be factored in as well.

I hope this helps clear up any confusion around GI and GL for you. Be well.
Dr. Russ

** Information on this web site is provided for informational purposes only and is not intended as a substitute for the advice provided by your physician or other healthcare professional. You should not use the information on this web site for diagnosing or treating a health problem or disease, or prescribing any medication or other treatment. **