Blood Glucose Control and the Glycemic Index

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A randomized clinical trial comparing low–glycemic index versus ADA dietary education among individuals with type 2 diabetes, by Yunsheng Ma and colleagues. Nutrition 28:45–56, 2008

What is the problem and what is known about it so far?

Carbohydrate foods have been classified by their glycemic index (GI), which measures their effect on blood glucose. The higher the index, the faster the food raises glucose levels. Low–GI diets have improved blood glucose in the short term in research trials. How well such diets work in real life and what their long-term effects are remain unknown.

Why did researchers do this particular study?

The researchers wanted to compare the effects of a diet featuring low–GI foods to those of a diet based on the American Diabetes Association (ADA) nutrition guidelines. The ADA recommends that people with diabetes get 45–65 percent of their total diet from carbohydrate foods.

Who was studied?

Forty people with poorly controlled type 2 diabetes took part in the study.

How was the study done?

Participants were divided into two groups to received eight nutrition education sessions focusing on either choosing low–GI foods or basing daily eating on ADA nutrition guidelines. Information was collected about A1C (a measure of average glucose levels over a span of a few months), diabetes medicine use, blood fat levels, weight, diet, physical activity, and other factors at the start, middle, and end of the 1-year study.

What did the researchers find?

The two groups significantly lowered their A1C levels by similar amounts and also had similar improvements in blood fats and weight. However, the low–GI group was less likely to have added or increased doses of diabetes medicines to achieve better blood glucose control.

What were the limitations of the study?

Attendance at the education sessions was lower in the GI group, which may have caused some participants to have trouble understanding and following the low–GI diet. Although many of the participants used cholesterol medicines, the study did not look at changes in those medicines, which may have affected the results related to blood fats. The researchers also did not find out the reasons some participants changed their diabetes medicines. Finally, the small number of participants meant that the study could not accurately measure possible small differences in A1C results between the two groups.

What are the implications of the study?

A low–GI diet may be an acceptable alternative to ADA diet recommendations. However, a larger trial is needed to confirm these findings.

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