A new study of overweight and obese people has shown little difference in impact between low-glycemic and high-glycemic diets for improving cardiovascular health and lowering diabetes risk.
Published in the Journal of the American Medical Association, this study was designed to test whether foods with a low-glycemic index can improve cardiovascular risk factors and lower risk of diabetes. Several popular diets have been built around this popular belief, even though the exact independent effect glycemic index has on these factors is not well understood.
The study, headed by Frank M. Sacks, M.D., of Brigham and Women's Hospital and Harvard Medical School, Boston, included 163 overweight adults either with prehypertension or stage 1 hypertension. Each was given at least two of four study diets that contained all of their meals, snacks, and calorie-containing beverages for a five-week period. The four study diets were:
- A high-glycemic, high-carbohydrate diet
- A low-glycemic index, high-carbohydrate diet;
- A high-glycemic index, low-carbohydrate diet
- A low-glycemic index, low-carbohydrate diet
All four diets were based on a healthful Dietary Approaches to Stop Hypertension (DASH)-type diet, which is rich in fruits, vegetables, and low-fat dairy foods, and low in saturated and total fat.
The results showed that found that at high dietary carbohydrate content, the low-glycemic index diet decreased insulin sensitivity; increased LDL cholesterol; and did not affect levels of high-density lipoprotein (HDL) cholesterol, triglycerides, or blood pressure compared to the high-glycemid index. At low carbohydrate content, the only difference between the two levels was a decrease in triglycerides for the low-glycemic index. The low-glycemic index, low-carbohydrate diet, compared with the high-glycemic index, high-carbohydrate diet, also yielded only one difference: a decrease in triglycerides. The authors ultimately concluded that “in the context of an overall DASH-type diet, using glycemic index to select specific foods may not improve cardiovascular risk factors or insulin resistance."
Published in WholeFoods Magazine, February 2015(online 12/17/2014)