Vegetable and nut intake and a Mediterranean dietary pattern seem to lower the risk of heart disease, according to a review of past studies.
However, the review also suggests that the consumption of trans-fatty acids and foods with a high glycemic index may be harmful to heart health.
Dr. Andrew Mente and his colleagues at the Population Health Research Institute carried out a systematic search for articles investigating dietary factors in relation to heart disease, published between 1950 and June 2007.
The researchers identified 146 prospective cohort studies that looked back on the habits of a particular group of individuals, and 43 randomised controlled trials wherein participants were randomly assigned to a dietary intervention or a control group.
They said that upon pooling the study results and applying a predefined algorithm, "we identified strong evidence of a causal elationship for protective factors, including intake of vegetables, nuts and monounsaturated fatty acids and editerranean, prudent and high-quality dietary patterns, and harmful factors, including intake of trans-fatty acids and foods with a high glycemic index or load and a western dietary pattern."
They write: "Among these dietary exposures, however, only a Mediterranean dietary pattern has been studied in randomised controlled trials and significantly associated with coronary heart disease."
The research team also found modest relationships supporting a causal relationship between intake of several other foods and vitamins and heart disease risk, including fish, omega-3 fatty acids from marine sources, folate, whole grains, alcohol, fruits, fibre and dietary vitamins E and C and beta carotene.
The study also supported causal relationships between vitamin E and ascorbic acid supplements, saturated and polyunsaturated fatty acids and total fats, alpha-linoleic acid, meat, eggs and milk.
"The modest or weak evidence of these dietary exposures is mostly consistent with the findings of randomised controlled trials, although randomised controlled trials have yet to be conducted for several factors," the authors write.
"Taken together, these findings support a causal relationship between only a few dietary exposures and coronary heart disease, whereas the evidence for most individual nutrients or foods is too modest to be conclusive.
"Although investigations of dietary components may help to shed light on mechanisms behind the benefits of dietary patterns, it is unlikely that modifying the intake of a few nutrients or foods would substantially influence coronary outcomes," they conclude. "Our findings support the strategy of investigating dietary patterns in cohort studies and randomized controlled trials for common and complex chronic diseases such as coronary heart disease," they add.
The study has been published in the Archives of Internal Medicine, one of the JAMA/Archives journals.