Not All Diets Pass the Heart-Healthy Test

Study Shows Mediterranean Diet Lowers Heart Disease Risk; Western Diet Gets Poor Marks

By Jennifer Warner
WebMD Health News

Reviewed By Louise Chang, MD

April 13, 2009 -- Despite claims that many foods and diets are heart healthy, a new review shows only some show strong evidence of lowering heart disease risk.

Researchers evaluated more than 50 years of research on diet and heart disease and found diets rich in vegetables, nuts, and those that follow a Mediterranean pattern with lots of fruits, vegetables, and fish have "strong evidence" of lowering the risk of heart disease.

In contrast, eating a Western-style diet, foods high in trans-fatty acids, or foods with a high glycemic index were shown to raise the risk of heart disease. Foods high in trans-fatty acids include processed baked goods and snacks and fried foods. Foods with a high glycemic index cause blood sugar levels to spike and include simple or refined carbohydrates like white bread, pasta, and rice.

Several other dietary factors -- including omega-3 fatty acids found in fish, whole grains, alcohol, vitamins E and C, beta carotene, folate, fruit, and fiber -- were shown to have moderate evidence to support a heart-healthy claim. But more research is needed to conclusively prove the relationship between these dietary factors and heart disease risk.

Heart-Healthy Claims Put to the Test

The review of diet and heart disease was conducted by Andrew Mente, PhD, of the Population Health Research Institute and colleagues; it was published in the Archives of Internal Medicine.

The researchers analyzed 146 studies that looked back at the dietary habits of a particular group of individuals in relation to their risk of heart disease as well as 43 studies in which people were assigned to a diet or a comparison group to measure the effect on heart disease risk.

Researchers pooled the results of the studies and then rated the strength of evidence behind the various heart-healthy diet claims.

The final results showed only three specific dietary factors had strong evidence behind them as proven heart disease fighters:

  • Vegetable-rich diet
  • Eating nuts rich in monounsaturated fatty acids like walnuts and other nuts
  • Following a Mediterranean-style diet high in vegetables, legumes, fruits, nuts, whole grains, cheese or yogurt, and fish

Of these, only a Mediterranean-style diet has been shown in randomized controlled studies to reduce the risk of heart disease.

Researchers also found strong evidence behind the negative effects of the following dietary factors on heart disease risk:

  • Following a Western-style diet high in processed meats, red meat, butter, refined grains, and high-fat dairy products
  • High-glycemic index foods
  • Trans-fatty acids

The evidence behind all other dietary factors was "too modest to be conclusive" according to researchers.

SOURCES: Mente, A. Archives of Internal Medicine, April 13, 2009; vol 169: pp 659-669. News release, American Medical Association.

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