A number of reviewers have examined studies investigating the relationship between coronary heart disease and stroke prior to 2000. Since then, several key studies have been published. Five studies have examined the relationship between wholegrain consumption, coronary heart disease (CHD) and cardiovascular (CVD) disease and found protection for either or both diseases. The researchers concluded that a relationship between wholegrain intake and CHD is seen with at least a 20% and perhaps a 40% reduction in risk for those who eat wholegrain food habitually vs those who eat them rarely. Notwithstanding the fact that fibre is an important component of wholegrains, many studies have not shown an independent effect of fibre alone on CHD events. Thus in terms of CHD prevention, fibre is best obtained from wholegrain sources. Wholegrain products have strong antioxidant activity and contain phytoestrogens, but there is insufficient evidence to determine whether this is beneficial in CHD prevention. Soluble fibre clearly lowers cholesterol to a small but significant degree and one would expect that this would reduce CHD events. There have been a small number of epidemiological studies showing soy consumption is associated with lower rates of heart disease. Countering the positive evidence for wholegrain and legume intake has been the Nurses Health Study in 2000 that showed women who were overweight or obese consuming a high glycaemic load (GL) diet doubled their relative risk of CHD compared with those consuming a low GL diet. Although the literature relating GL with CHD events is somewhat mixed, the relationship with risk factors such as HDL cholesterol, triglyceride and C reactive protein is relatively clear. Thus, carbohydrate-rich foods should be wholegrain and, if they are not, then the lowest glycaemic index (GI) product should be used. Promotion of carbohydrate foods should be focused on wholegrain cereals because these have proven to be associated with health benefits. There is insufficient evidence about whether the addition of other components of wholegrains such as polyphenolics or minerals (such as magnesium or zinc) would improve the health benefits of refined grain foods and this needs investigation. Whether adding bran to refined carbohydrate foods can improve the situation is also not clear, and it was found that added bran lowered heart disease risk in men by 30%. This persisted after full adjustment (including GL) suggesting, at least in men, that fibre may be more important than GI. Thus there are two messages: The intake of wholegrain foods clearly protects against heart disease and stroke but the exact mechanism is not clear. Fibre, magnesium, folate and vitamins B6 and vitamin E may be important. The intake of high GI carbohydrates (from both grain and non-grain sources) in large amounts is associated with an increased risk of heart disease in overweight and obese women even when fibre intake is high but this requires further confirmation in normal-weight women.
Recommendation: Carbohydrate-rich foods should be wholegrain and if they are not, then the lowest GI product available should be consumed. Glycemic index is largely irrelevant for foods that contain small amounts of carbohydrate per serve (such as most vegetables).