According to findings published in this week’s Archives of Internal Medicine, modest relationships were found supporting omega-3 fatty acids, folate, whole grains, alcohol, fruits, fibre and dietary vitamins E and C and beta carotene, for reductions in the risk of heart disease.
On the other hand, trans-fatty acids and foods with a high glycemic index (GI) were associated with detrimental effects on heart health, wrote the researchers, led by Andrew Mente, from the Population Health Research Institute.
"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," wrote the researchers.
"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."
The review supports the Mediterranean diet pattern, rich in cereals, wine, fruits, nuts, legumes and whole grains, fish and olive oil, and low in dairy, meat, junk food and fat. The dietary pattern has been linked to longer life, less heart disease, and protection against some cancers. The diet's main nutritional components include beta-carotene, vitamin C, tocopherols, polyphenols, and essential minerals.
Mente and his co-workers conducted a systematic review of 146 prospective cohort studies and 43 randomised controlled trials published between 1950 and 2007.
The data was pooled and a predefined algorithm applied. “We identified strong evidence of a causal relationship for protective factors, including intake of vegetables, nuts and monounsaturated fatty acids and Mediterranean, 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 wrote.
"Among these dietary exposures, however, only a Mediterranean dietary pattern has been studied in randomized controlled trials and significantly associated with coronary heart disease."
Modest relationships were also observed linking reduced risk of heart disease and fish, omega-3 fatty acids from marine sources, folate, whole grains, alcohol, fruits, fibre and dietary vitamins E and C and beta carotene, report the researchers.
Weak evidence also a protective role for supplemental vitamin E and vitamin C, saturated and polyunsaturated fatty acids and total fats, alpha-linoleic acid (ALA), meat, eggs and milk.
"The modest or weak evidence of these dietary exposures is mostly consistent with the findings of randomized controlled trials, although randomized controlled trials have yet to be conducted for several factors," wrote the authors.
"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."
Source: Archives of Internal Medicine 13 April 2009, Volume 169, Number 7, Pages 659-669“A Systematic Review of the Evidence Supporting a Causal Link Between Dietary Factors and Coronary Heart Disease” Authors: A. Mente, L. de Koning, H.S. Shannon, S.S. Anand