Low glycaemic index diets for coronary heart disease

Abstract

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 randomised controlled trials (RCTs) in this area. Objectives To review evidence from RCTs assessing the relationship between the consumption of low GI diets and the effects on coronary heart disease (CHD) and related risk factors in people who have established CHD or risk factors. Search strategy We searched CENTRAL on The Cochrane Library (Issue 2, 2006), MEDLINE (1966 to July 2006), EMBASE (1980 to July 2006) and CINAHL (1982 to July 2006). We checked references and contacted experts in the field. No language restrictions were applied. Selection criteria We selected RCTs that assessed the effects of low GI diets, over a minimum of 4 weeks, on CHD and risk factors for CHD. Participants included were adults with at least one major risk factor for CHD e.g. abnormal lipids, diabetes or being overweight or who had previously been diagnosed with CHD. Data collection and analysis Two reviewers independently assessed trial quality and extracted data. Authors of the included studies were contacted for additional information where necessary. Main results Twenty-one RCTs were included, with a total of 713 participants randomised. No studies were found that reported the effect of low GI diets on CHD mortality or CHD events and morbidity. All 21 included studies report the effect of low GI diets on risk factors for CHD. Meta-analysis detected limited and weak evidence of slightly lower total cholesterol with low glycaemic index diets. However, when only studies on diabetics were included in the analysis, no evidence of an effect on total cholesterol was found. There is little evidence from the combination of studies in meta-analysis that low glycaemic index diets have an effect on LDL cholesterol, HDL cholesterol, triglycerides, glycosylated haemoglobin (HbA1c), fasting glucose or fasting insulin levels. However, the majority of individual studies do report slightly lower levels of glycosylated haemoglobin (HbA1c) with low GI diets. Authors' conclusions There is no evidence from RCTs to show an effect of low GI diets on coronary heart disease. Weak evidence for minor effects on some CHD risk factors was found. Many of the trials identified were short-term, of poor quality and did not have sufficient power to detect clinically important differences. The combined evidence from the studies suggests that any beneficial effect of low glycaemic index diets on CHD and its risk factors is small. There is a need for well designed, adequately powered, randomised controlled studies, of greater than 12 weeks duration to assess the true effects of low glycaemic index diets for CHD.