Diet May Trump Glycemic Index

Low glycemic index diet did not lower diabetes risk or improve heart health more than overall healthy diet

/ Author:  / Reviewed by: Joseph V. Madia, MD Beth Bolt, RPh

(RxWiki News) Lowering your risk for health problems like diabetes and heart disease through diet may be simpler than once thought. Patients may need to simply focus on eating healthy, natural foods in general, rather than worrying about how healthy foods affect factors like blood sugar.

A new study found that a low glycemic index diet didn't improve heart health or lower diabetes risk any more than simply eating plenty of fruits, vegetables and low-fat or nonfat dairy products.

Patients sometimes use the glycemic index to help manage the impact of foods on their blood sugar. The glycemic index gives an idea of how much and how fast a carbohydrate-containing food will raise blood glucose (sugar). White bread and pretzels, for instance, are high on the glycemic index. Most fruits and beans are low.

This research was led by Frank M. Sacks, MD, of Brigham and Women’s Hospital and Harvard Medical School in Boston, and Lawrence J. Appel, MD, director of the Welch Center for Prevention, Epidemiology and Clinical Research at Johns Hopkins Medicine in Baltimore.

"We were really surprised," Dr. Appel said in a press release. "We did not detect any clear benefit of the low glycemic index diets on the major risk factors for heart disease, and we found no evidence of benefit for diabetes prevention."

These researchers recruited 163 overweight adults with prehypertension or stage 1 hypertension. These are both conditions where blood pressure is higher than normal.

Patients were randomly assigned to follow one of four healthful DASH-type diets. DASH stands for Dietary Approaches to Stop Hypertension. The National Heart, Lung, and Blood Institute (NHLBI) sponsored research to develop these eating plans. They stress consuming vegetables, fruits and fat-free or low-fat dairy products. These diets include whole grains, fish, poultry, beans, seeds, nuts and vegetable oils. They also limit sodium, sweets, sugary beverages and red meats.

Each of the four diets in the study provided the same number of calories. The calories, however, came from foods that were either high or low in carbohydrates, and also either high or low on the glycemic index.

After five weeks, these researchers found that a diet that had a low glycemic index and was low in carbs did not appear to affect insulin sensitivity, blood pressure, LDL (“bad”) cholesterol or HDL (“good”) cholesterol — compared to a diet that had a high glycemic index and was high in carbs. Insulin is a hormone that helps blood sugar get into cells and give them energy. Poor insulin sensitivity may lead to type 2 diabetes, a condition where there is too much sugar in the blood.

"Get back to the basics that most people already know," Dr. Appel said. "Try to eat fruits, vegetables and whole grains. Try to avoid sweets, salt, and foods high in saturated and trans fats. People who follow these principles will reap the benefits."

In an editorial about this study, Robert H. Eckel, MD, with the University of Colorado’s Anschutz Medical Campus in Aurora, said the study suggests that, for most patients, the glycemic index of food is less relevant than the overall dietary pattern.

"The unexpected findings of the study suggest that the concept of glycemic index is less important than previously thought, especially in the context of an overall healthy diet, as tested in this study," Dr. Eckel wrote. "These findings should therefore direct attention back to the importance of maintaining an overall heart-healthy lifestyle, including diet pattern."

The study and editorial were published Dec. 17 in JAMA.

This research was funded by the NHLBI, the National Institute of Diabetes and Digestive and Kidney Diseases, the Harvard Clinical and Translational Science Center, the National Center for Advancing Translational Science and Brigham and Women’s Hospital. Dr. Sacks was an expert witness in litigation involving POM Wonderful, Hershey, Unilever and Keebler.


Review Date: 
December 16, 2014
Last Updated:
March 12, 2015