Diets low in "glycemic index" is touted as a way to help prevent diabetes and heart disease. But a new study suggests that as long as people are eating healthily, they don't need to obsess over glycemic index.
"The study results were very surprising," says lead author Frank M. Sacks, MD, a physician and researcher in Brigham and Women's Hospital's Channing Division of Network Medicine. "Our findings demonstrated that using glycemic index to select specific foods did not improve LDL cholesterol, HDL cholesterol, triglycerides, blood pressure or insulin resistance."
The findings, reported online on Dec. 16 in the Journal of the American Medical Association, were unexpected, experts said. But they also called the results "good news."
"Low-GI diets are difficult to follow," said Dr. Frank Sacks, the lead researcher on the study and a professor of cardiovascular disease prevention at the Harvard School of Public Health.
"If you don't have to worry about foods' glycemic index, that makes it easier to follow a healthy diet," Sacks said.
Glycemic index is a measure of how an individual food affects blood sugar levels. Simply put, a food with a high GI like white bread or potatoes causes a surge in blood sugar; a food with a low GI many vegetables, for example produces a more gradual change in blood sugar.
Over the course of five weeks, participants were given one of four complete diets, each of which was a variation of a diet such as the DASH or the Mediterranean diet that are recommended by US national dietary guidelines.
Insulin sensitivity, levels of low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides and systolic blood pressure were the outcomes that interested the researchers the most.
They also looked at the effects of glycemic index when total carbohydrate intake is high, as it is on the DASH diet, or low, as is the case with the Omni Heart diet or Mediterranean diet.
"We studied diets that had a large contrast in glycemic index, while at the same time we controlled intake of total carbohydrates and other key nutrients, as well as maintained baseline body weight," says Dr. Sacks. "We found that composing a healthful diet with low-glycemic index carbohydrate containing foods rather that high-glycemic index foods did not improve insulin sensitivity, HDL or LDL cholesterol levels or systolic blood pressure."
According to Eckel, the findings show that "it's the overall quality of the dietary pattern that really matters."
"I really dislike the idea of 'bad' foods and 'good' foods," Eckel said. "If you have some cake and ice cream at a birthday party, you don't have to feel guilty."
He added, however, that the findings do not necessarily apply to people who already have type 2 diabetes. "With diabetes, GI might be more important," Eckel said.
The study was published in the Journal of the American Medical Association.
