Measuring blood sugar

Believe it or not, all carbs aren’t the same, says Amanda Smith, clinical dietitian at Georgetown University Hospital.

With the recent low-carbohydrate craze, dieters avoid foods such as pasta and potatoes to limit fluctuations in their blood sugar. The glycemic index ranks carbohydrates by how much a person’s blood sugar rises immediately after eating.

Ms. Smith usually uses the index when teaching diabetic patients how to adjust their diets, but recently, people on low-carb diets have been using the table for weight-loss purposes.

She says she doubts an entire diet should be designed specifically on the index’s information.

“Everybody is different,” Ms. Smith says. “Somebody may eat a baked potato, and it may not make their blood sugar go up as much as the next person.”

Other health professionals think the concept of the index is too complicated to explain and put into practice.

Proponents of basing a diet on the glycemic index, however, maintain that eating foods lower on the list could provide many health benefits, including weight loss.

The glycemic index compares foods’ carbohydrate content, gram for gram, says Dr. Thomas Wolever, a professor in the department of nutritional sciences at the University of Toronto.

Dr. Wolever helped create the table with Dr. David Jenkins, who is a professor in the same department at the university. Their goal was to make a table for diabetic patients, listing the foods that don’t cause large increases in blood sugar.

At the time, glucose was used as the standard to which other foods were compared. Since then, tests have been done using white bread as the reference, but Dr. Wolever still prefers to use glucose. Dr. Wolever studied the blood sugar response of about 40 subjects and averaged the values of their tests to create the glycemic index.

In 1981, the doctors made public their research, which provided a new way to classify carbohydrates. Generally, the carbohydrates with the highest glycemic indexes, including white or wheat bread, bagels, mashed potatoes and most breakfast cereals, break down rapidly during digestion, causing a fast rise in blood sugar.

Carbohydrates with the lower glycemic indexes, including cold potato salad, pasta, oatmeal, legumes, barley, parboiled rice and whole-grain breads, break down slowly. After digestion, they release glucose into the blood stream at a gradual rate, which causes a smaller rise in the blood sugar.

Therefore, eating according to the glycemic index would improve a person’s control of diabetes, he says.

“It seems quite important that the rate to which we get the carb into the body can affect both health and disease,” Dr. Wolever says. “Where this will all lead, I don’t know. There is evidence that low [glycemic index] affects risks for heart disease, diabetes, cancer, and it can affect body weight regulation, thinking and memory.”

Eating foods low on the glycemic index doesn’t mean a person would never eat a food that is higher on the table, such as white bread, Dr. Wolever says. If a person wants to eat a food such as rice, Dr. Wolever suggests choosing a type of rice lower on the list — parboiled rice, for example.

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