Wholegrain foods encompass a range of products and examples are wholegrain wheat, rice, maize and oats. The term wholegrain also includes milled wholegrains such as oatmeal and wholemeal wheat. The evidence found by this review is limited to wholegrain oats, and to changes in lipids as an outcome. There is a lack of studies on other wholegrain foods or diets. There is some evidence from this review that oatmeal foods can beneficially lower lipid levels such as low density lipoproteins (LDL) cholesterol and total cholesterol in those previously diagnosed with risk factors for coronary heart disease (CHD) even with relatively short interventions. However, the results should be interpreted with caution because the trials found are small, of short duration and many were commercially funded. No studies were found that reported the effect of wholegrain foods or diets on deaths from, or occurrence of CHD.
Despite the consistency of effects seen in trials of wholegrain oats, the positive findings should be interpreted cautiously. Many of the trials identified were short term, of poor quality and had insufficient power. Most of the trials were funded by companies with commercial interests in wholegrains. There is a need for well-designed, adequately powered, longer term randomised controlled studies in this area. In particular there is a need for randomised controlled trials on wholegrain foods and diets other than oats.
There is increasing evidence from observational studies that wholegrains can have a beneficial effect on risk factors for coronary heart disease (CHD).
The primary objective is to review the current evidence from randomised controlled trials (RCTs) that assess the relationship between the consumption of wholegrain foods and the effects on CHD mortality, morbidity and on risk factors for CHD, in participants previously diagnosed with CHD or with existing risk factors for CHD.
We searched CENTRAL (Issue 4, 2005), MEDLINE (1966 to 2005), EMBASE (1980 to 2005), CINAHL (1982 to 2005), ProQuest Digital Dissertations (2004 to 2005). No language restrictions were applied.
We selected randomised controlled trials that assessed the effects of wholegrain foods or diets containing wholegrains, over a minimum of 4 weeks, on CHD and risk factors. Participants included were adults with existing CHD or who had at least one risk factor for CHD, such as abnormal lipids, raised blood pressure or being overweight.
Two of our research team independently assessed trial quality and extracted data. Authors of the included studies were contacted for additional information where this was appropriate.
Ten trials met the inclusion criteria. None of the studies found reported the effect of wholegrain diets on CHD mortality or CHD events or morbidity. All 10 included studies reported the effect of wholegrain foods or diets on risk factors for CHD. Studies ranged in duration from 4 to 8 weeks. In eight of the included studies, the wholegrain component was oats. Seven of the eight studies reported lower total and low density lipoproteins (LDL) cholesterol with oatmeal foods than control foods. When the studies were combined in a meta-analysis lower total cholesterol (-0.20 mmol/L, 95% confidence interval (CI) -0.31 to -0.10, P = 0.0001 ) and LDL cholesterol (0.18 mmol/L, 95% CI -0.28 to -0.09, P < 0.0001) were found with oatmeal foods. However, there is a lack of studies on other wholegrains or wholegrain diets.