A major new study by researchers at McMaster University clarifies what foods and dietary patterns are best for reducing the risk of heart disease. For the first study of its kind, researchers systematically evaluated almost 200 studies investigating dietary patterns and their link to coronary heart disease (CHD) conducted between 1950 and 2007 in the United States, Europe and Asia.

The study concludes there are certain food groups or dietary patterns, that are beneficial, including vegetables, nuts, monounsaturated fatty acids, and an overall 'healthy' dietary patterns such as the Mediterranean diet which incorporates generous amounts of fruits and vegetables, healthy fats, such as olive and canola oil, small portions of nuts, red wine in moderation, very little red meat and fish on a regular basis. In addition, the researchers conclude there is strong evidence which supports that certain dietary factors such as glycemic index/load of foods and trans fatty acids are harmful.

Their study, A Systematic Review of the Evidence Supporting a Causal Link Between Dietary Factors and Coronary Heart Disease, appears in the Monday, April 13 issue of the Archives of Internal Medicine.

"We hope our comprehensive review will clarify healthy and harmful foods as related to heart disease for the general public," said senior author Dr. Sonia Anand. She is a professor of medicine at McMaster University, holds the Heart and Stroke Foundation of Ontario and Michael G. DeGroote Chair in Population Health Research, and she is a researcher in the Population Health Research Institute.

"Concluding there is strong evidence that certain dietary patterns, or food groups which are clearly beneficial or harmful, is an easy message for health professionals to send to the general public," said Dr. Anand. "People should focus on consuming a healthy dietary pattern, such as the Mediterranean diet, high in fruits and vegetables, and a diet low in trans fat."

Dr. Anand hopes the study will encourage health professionals and dieticians to present information to the public in a less factual and more people-friendly manner.

For their study, the McMaster researchers used a set of criteria linking cause and health outcomes. The lead author was Andrew Mente, PhD and a post-doctoral fellow funded by the Heart and Stroke Foundation.

He says: "The findings highlight the importance of improving overall diet quality to maintain good cardiovascular health.

"People need to be cautious and not become too preoccupied with a few individual nutrients or food items, while ignoring diet in its totality. In fact, the evidence gathered on most individual dietary components is too modest to be conclusive, and in many instances, clinical trials evaluating coronary outcomes are absent.

"On the other hand, the evidence clearly shows that adherence to a quality dietary pattern such as the Mediterranean diet is highly protective against coronary heart disease and total mortality."

Dr. Marco Di Buono, the director of research of the Heart and Stroke Foundation of Ontario, says: "The results of studies like these help Canadians understand exactly what they should be putting into their grocery carts, which is where they take the first step towards heart healthy eating,"

The study raises a note of caution because all the evidence isn't in yet about the current general consensus that a reduced consumption of saturated -fatty acids and a higher intake of fruits and vegetables, polyunsaturated fatty acids including plant omega-3 fatty acids and whole grains is beneficial.

"This is cause for concern," the article says, "because dietary advice to limit the intake of a certain nutrient (dietary fat) may result in increased consumption of another (carbohydrates) which can have adverse effects on CHD risk factors.

"Moreover, without large prospective studies in which multiple health outcomes are evaluated, recommendations to modify a dietary component may decrease the likelihood of one chronic disease (CHD) at the cost of increasing another (cancer)," the researchers said in their paper.

Dr. Anand said the paper has a message for the scientific community. "What we have demonstrated is that, for some food groups and nutrients, there has been relatively weak information. Even though one study may be positive, there may be three others that are negative or conflicting. We really need to look at the totality of the evidence in the field before promoting something to the public at large," she said.

Veronica McGuire
Media Relations
McMaster University