Low glycaemic index diets for coronary heart disease.

BACKGROUND The glycaemic index (GI) is a physiological measure of the ability of a carbohydrate to affect blood glucose. Interest is growing in the low GI carbohydrate concept for the clinical management of people at risk of, or with established coronary heart disease. There is a need to review the current evidence from controlled trials in this area. OBJECTIVES The primary objective is to review the current evidence from RCTs that assess the relationship between the consumption of low glycaemic index diets and the effects on coronary heart disease and on risk factors for coronary heart disease. SEARCH STRATEGY We searched CENTRAL (Issue 4, 2003), MEDLINE (1966 to 2003), EMBASE (1980 to 2003) and CINAHL (1982 to 2003). We also contacted experts in the field. SELECTION CRITERIA We selected randomised controlled trials that assessed the effects of low glycaemic index diets, over a minimum of 4 weeks, on coronary heart disease (CHD) and risk factors. Participants included were adults who carry at least one major risk factor for coronary heart disease such as abnormal lipids, diabetes or being overweight. DATA COLLECTION AND ANALYSIS Two of our research team independently assessed trial quality and extracted data. Authors of the included studies were contacted for additional information when this was appropriate. MAIN RESULTS Fifteen randomised controlled trials met the inclusion criteria. No studies found reported the effect of low glycaemic index diets on CHD mortality or CHD events and morbidity. All fifteen included studies report the effect of low glycaemic index diets on major risk factors for CHD. Meta-analysis detected limited and weak evidence of a relationship between low glycaemic index diets and slightly lower total cholesterol, compared with higher glycaemic index diets. There is also limited and weak evidence of a small reduction in HbA1c after 12 weeks on low glycaemic index diets but not at 4 to 5 weeks. There is no evidence that low glycaemic index diets have an effect on LDL cholesterol or HDL cholesterol, triglycerides, fasting glucose or fasting insulin levels. REVIEWERS' CONCLUSIONS The evidence from randomised controlled trials showing that low glycaemic index diets reduces coronary heart disease and CHD risk factors is weak. Many of the trials identified were short-term, of poor quality and conducted on small sample sizes. There is a need for well designed, adequately powered, randomised controlled studies, of greater than 12 weeks duration to assess the effects of low glycaemic index diets for CHD.