If you generally eat a heart-healthy diet, then you might have one fewer factor to worry about: the "glycemic index" of the carbs you eat, new research suggests.
In a new study, researchers looked at how people's health is affected by the types of carbs they eat, using one measure of carbohydrates called the glycemic index. This index is a number, between 1 and 100, that reflects how much a given carb raises your blood sugar levels. For example, carbs such as apples and oatmeal have a low glycemic index, meaning they raise blood sugar less than carbs with a higher glycemic index, such as white bread and corn flakes.
The researchers at Johns Hopkins University School of Medicine and Harvard Medical School set out to examine whether healthy diets with a low glycemic index would provide more heart health benefits compared with similarly healthy diets that have a higher glycemic index.
The researchers gave special diets to 163 overweight men and women for five weeks, and tracked their blood pressure, cholesterol levels and sensitivity to insulin. The participants were on four different diets that all contained the same number of calories, but two were high in carbohydrates and two were low in carbohydrates. Among the two that were high in carbs, one had a high glycemic index and the other had a low index. Similarly, of the two diets that were low in carbs, one had a high glycemic index and the other had a low one.
The results showed that the glycemic index of the diet didn't matter. The participants on diets with a low glycemic index did not have improvements in their insulin sensitivity, cholesterol levels or blood pressure during the study, according to the findings published today (Dec. 16) in the journal JAMA.
"We were really surprised," says co-author Dr. Lawrence Appel, a professor of medicine at Johns Hopkins. "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."
All four diets in the study were based on the Dietary Approaches to Stop Hypertension (DASH)diet. The DASH diet is designed to help treat or prevent high blood pressure by reducing people's salt intake and including foods rich in nutrients that help lower blood pressure, such as potassium, calcium and magnesium.
"The unexpected findings" of the study suggest that the concept of glycemic index is less important than previously thought," Dr. Robert Eckel, a professor of medicine at the University of Colorado, wrote in an editorial accompanying the study. "These findings should therefore direct attention back to the importance of maintaining an overall heart-healthy lifestyle, including diet pattern," he said.
An overall heart-healthy lifestyle includes the basic rules that most people already know, Appel said. "Don't drink sugar-sweetened drinks. 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," he said.