A diet rich in vegetables and fruits and low in meat is most beneficial to heart health, concludes a comprehensive review of studies dating as far back as 1950.

For the review, researchers at McMaster University systematically evaluated almost 200 studies conducted between 1950 and 2007 in the United States, Europe and Asia, that looked at dietary patterns and their link to heart disease.

They conclude that an overall "healthy" dietary pattern, such as the Mediterranean diet is most beneficial. A Mediterranean diet incorporates vegetables, fruit, healthy fats such as olive and canola oil, small portions of nuts, fish, red wine in moderation, and very little red meat.

In addition, there is strong evidence that certain dietary factors are harmful, such as foods with a high glycemic index, and trans fatty acids, says senior author Dr. Sonia Anand, a professor of medicine at McMaster and a researcher in the Population Health Research Institute.

"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," she says.

The study, "A Systematic Review of the Evidence Supporting a Causal Link Between Dietary Factors and Coronary Heart Disease," appears in the Archives of Internal Medicine.

The authors write that although "a wealth of literature" has been published on the relationship between diet and heart disease, "the strength of the evidence supporting valid associations has not been evaluated systematically in a single investigation."

"We hope our comprehensive review will clarify healthy and harmful foods as related to heart disease for the general public," said Anand.

For their study, the McMaster researchers reviewed 146 prospective cohort studies (looking at the habits of a particular group of individuals) and 43 randomized controlled trials (where participants are randomly assigned to a dietary intervention or a control group).

When the researchers pooled the study results and applied a predefined algorithm, "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 write.

Andrew Mente, a post-doctoral fellow funded by the Heart and Stroke Foundation, says people need to not become too preoccupied with a few individual nutrients or food items. It's a dietary pattern that is most important.

"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."

They note that not all the evidence is in about what constitutes a healthy diet and that much more research is needed on certain food groups and nutrients.

For example, it isn't known whether dietary advice about limiting the intake the amount of dietary component, such as saturated fat, may decrease the likelihood of one chronic disease, such as heart disease, at the cost of increasing another disease such as cancer.

Dr. Anand says: "We really need to look at the totality of the evidence in the field before promoting something to the public at large."