The glycemic index ranks foods on how they affect our blood sugar levels. This index measures how much your blood sugar increases after you eat.
The real problem is carbohydrates.
When you make use of the glycemic index to prepare healthy meals, it helps to keep your blood sugar levels under control. This is especially important for people with diabetes, although athletes and people who are overweight also stand to benefit from knowing about this relatively new concept in good nutrition.
Recent studies of large numbers of people with diabetes show that those who keep their blood sugar under tight control best avoid the complications that this disease can lead to. The experts agree that what works best for people with diabetes—and probably everyone—is regular exercise, little saturated and trans fat, and a high-fiber diet. That is excellent advice—as far as it goes.
The real problem is carbohydrates, and that's what the glycemic index is all about. Foods high in fat or protein don’t cause your blood sugar level to rise much.
The official consensus remains that a high-carbohydrate diet is best for people with diabetes. However, some experts recommend a low-carbohydrate diet, because carbohydrates break down quickly during digestion and can raise blood sugar to dangerous levels. A low-glycemic diet avoids both extremes.
Many carbohydrate-rich foods have high glycemic indexes, and certainly are not good in any substantial quantity for people with diabetes. Other carbohydrates break down more slowly, releasing glucose gradually into our blood streams and are said to have lower glycemic indexes.
The really shocking results of G.I. studies are in which foods produce the highest glycemic response. They include many of the starchy foods we eat a lot of, including most bread, most breakfast cereals, and baked potatoes. But table sugar—long believed to be the worst thing for people with diabetes—isn’t as high on the index.
Low glycemic foods include beans, barley, pasta, oats, and some types of rice. Acidic fruits have low glycemic indexes. Likewise, vinegar and lemon juice—as in salad dressing—help reduce the glycemic load.
A lot of people still think that it is plain table sugar that people with diabetes need to avoid. The experts used to say that, but the glycemic index shows that starchy complex carbohydrates, like baked potatoes, can be even worse.
Before the development of the glycemic index beginning in 1981, scientists assumed that our bodies absorbed and digested simple sugars quickly, producing rapid increases in our blood sugar level. This was the basis of the advice to avoid sugar, a proscription recently relaxed by the American Diabetes Association and others.
Many of the glycemic index results have been surprises. For example, baked potatoes have a glycemic index considerably higher than that of table sugar.
A more pleasant surprise is the very low glycemic index of a tasty bean called chana dal, which is the subject of a separate article here. Another pleasant surprise is pearled barley, which has the lowest glycemic index of any grain.
Other Important Diet Considerations
The glycemic index should not be your only criterion when selecting what to eat. The total amount of carbohydrate, the amount and type of fat, and the fiber and salt content are also important dietary considerations. The glycemic index is most useful when deciding which high-carbohydrate foods to eat. But don’t let the glycemic index lull you into eating more carbohydrates than your body can handle. The number of grams of carbohydrate we consume is awfully important. Make sure you know the carbohydrate content of the foods you eat by studying the nutritional information on the package.
Factors such as variety, cooking, and processing may effect a food’s GI. Foods particularly sensitive to these factors include bananas, rice, and potatoes.
In addition, the glucose response to a particular food may be somewhat individual. So it is probably a good idea to carefully watch your own blood sugar after eating foods you have questions about and determine if they have high or low GI for you. If you find a specific food produces an unexpected result, either high or low, take note of it and incorporate that into your meal planning. Also note that the numbers vary from study to study. This may be due to variations in the individuals in a particular study, other foods consumed at the same time, or different methods of preparation, since your body can absorb some foods better when they are well cooked.
Most of the foods tested are high in carbohydrates. Some may wonder at the gaps—why other high-carbohydrate low-calorie foods like celery (or tomatoes or similar foods) have never been tested. The problem is a technical one for the testers, because they would be so hard put to get anyone to volunteer to eat 50 grams of carbohydrate from celery—it’s just too much celery to think about! Essentially, from a glycemic index standpoint, celery and foods like it can be considered as free foods. I now have a list of the common free foods on-line at http://www.mendosa.com/freefoods.htm.
Some people wonder if the glycemic index can predict the effect of a mix meal containing foods with very different indexes. Studies have shown that it does that job very well, too.
You can quite readily predict the glycemic index of a mixed meal. Simply multiply the percent of total carbohydrate of each of the foods by its glycemic index and add up the results to get the glycemic index of the meal as a whole.
Scientists have so far measured the glycemic indexes of about 750 high-carbohydrate foods. The key is to eat little of those foods with a high glycemic index and more of those foods with a low index. Where can you find what these foods are? See Glycemic Index Lists.
This article originally appeared in Diabetes Digest, April 1999.