Clinical Question

For patients with risk factors for coronary heart disease (CHD), does a low glycemic index diet reduce heart disease or improve risk factors?

Evidence-Based Answer

There is limited, weak evidence that a low glycemic index diet improves risk factors for CHD, but there are no randomized controlled trials (RCTs) showing a reduction in morbidity or mortality. (SORT rating C)

Practice Pointers

CHD is associated with high fat intake. However, there is uncertainty regarding how rapidly-metabolized dietary carbohydrates may affect the risk for heart attack and stroke. The glycemic index is a measure of the effect of dietary carbohydrate on blood glucose, on a scale from zero to 100; higher numbers correspond to a greater effect.

Kelly and colleagues systematically reviewed RCTs to determine whether a low glycemic index diet decreased mortality or CHD events (patient-oriented outcomes) or had a beneficial effect on risk factors for CHD such as abnormal lipids, glucose metabolism, blood pressure, weight, and clotting factors (surrogate markers that may or may not affect patient outcomes). Fifteen trials lasting four weeks or more were identified. Interventions included dietary advice or a prescribed diet for adult outpatients with at least one major risk factor. None of the studies reported morbidity or mortality. The studies were of poor quality and had too few patients to identify clinically important effects. There was a small reduction in A1C (0.45 percent) and total cholesterol levels (6.6 mg per 100 mL [0.17 mmol per L]). However, these outcomes were not sufficient to recommend low glycemic index diets for patients with risk factors for CHD.

Despite the lack of supporting evidence, several organizations recommend diets rich in complex carbohydrates for patients with risk factors for CHD. The National Cholesterol Education Program (NCEP) recommends that 50 to 60 percent of calories come from foods rich in complex carbohydrates, including grains (especially whole grains), fruits, and vegetables¹; this is essentially a low glycemic index diet. The American Dietetic Association supports the dietary recommendations of the NCEP for patients with hyperlipidemia.² The U.S. Preventive Services Task Force recommends intensive behavioral dietary counseling for adult patients with hyperlipidemia and other known risk factors for cardiovascular disease, but does not specify which diet should be recommended.³