Public Release: 

Low glycemic diet does not improve risk factors for cardiovascular disease and diabetes

New research indicates that a low glycemic diet does not improve insulin sensitivity, lipid levels or blood pressure

Brigham and Women's Hospital

Boston, MA-- Nutrition experts are continually debating the nutritional value of carbohydrate-containing foods and whether some are healthier than others. High carbohydrate foods are classified by how much they increase blood sugar; known as glycemic index. In new findings led by researchers at Brigham and Women's Hospital (BWH) in Boston and Johns Hopkins University (JHU) in Baltimore, researchers looked at glycemic index' effect on cardiovascular disease (CVD) and diabetes and found that low glycemic diets did not improve insulin sensitivity or cardiovascular risk factors. These findings are published in JAMA on December 17, 2014.

"The study results were very surprising. We hypothesized that a low glycemic index would cause modest, though potentially important improvements in insulin sensitivity and CVD risk factors," explained Frank M. Sacks, MD, a physician and researcher in BWH's Channing Division of Network Medicine BWH and lead author of this study. "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 researchers conducted a randomized controlled trial in which 163 overweight adults with elevated blood pressure were given one of four complete diets that contained all of their meals, snacks and beverages, each for five weeks. Each diet was a variation of a healthful dietary pattern as recommended by our national dietary guidelines, such as the DASH and Mediterranean diets. Researchers measured five outcomes including insulin sensitivity, levels of low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides and systolic blood pressure. Additionally, the effects of glycemic index when total carbohydrate is high, as in the DASH diet, or low, such as the OmniHeart diet or Mediterranean diet, were observed.

"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," explained 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.

The researchers note that future studies are needed to see if low glycemic index diets are helpful with type 2 diabetes, or for long-term weight loss. Previous research has shown inconsistent results on whether low glycemic index helped people lose weight.

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This research was supported by an investigator-initiated grant from the National Heart Lung and Blood Institute (R01HL084568) and received additional support from National Institute of Diabetes and Digestive and Kidney Diseases (R21DK098720-02) the Harvard Clinical and Translation Science Center (8Ul1TR0001750-05) from the National Center for Advancing Translational Science; and the general clinical research center at Brigham and Women's Hospital (M01-02635).

Brigham and Women's Hospital (BWH) is a 793-bed nonprofit teaching affiliate of Harvard Medical School and a founding member of Partners HealthCare. BWH has more than 3.5 million annual patient visits, is the largest birthing center in New England and employs nearly 15,000 people. The Brigham's medical preeminence dates back to 1832, and today that rich history in clinical care is coupled with its national leadership in patient care, quality improvement and patient safety initiatives, and its dedication to research, innovation, community engagement and educating and training the next generation of health care professionals. Through investigation and discovery conducted at its Biomedical Research Institute (BRI), BWH is an international leader in basic, clinical and translational research on human diseases, more than 1,000 physician-investigators and renowned biomedical scientists and faculty supported by nearly $650 million in funding. For the last 25 years, BWH ranked second in research funding from the National Institutes of Health (NIH) among independent hospitals. BWH continually pushes the boundaries of medicine, including building on its legacy in transplantation by performing a partial face transplant in 2009 and the nation's first full face transplant in 2011. BWH is also home to major landmark epidemiologic population studies, including the Nurses' and Physicians' Health Studies and the Women's Health Initiative. For more information and resources, please visit BWH's online newsroom.

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