Dr. James N. Cooper, of George Mason University, and Michael J. Sheridan, of Inova Fairfax Hospital, found that in people with moderately high cholesterol levels, a daily diet consisting of 15 percent of calories from pistachios -- about two to three ounces or one to two handfuls of kernels -- over a four-week period favorably improved some blood lipid levels.

"These results are exciting because the research indicates that adding pistachios to the daily diet can help protect the heart without a dramatic dietary lifestyle change," Cooper said in a statement.

The study, published in the Journal of the American College of Nutrition, challenges the previously-held belief that a low-fat diet is best for heart health.

Studies now show that a diet with a moderate amount of healthy mono-unsaturated fat, like the kind found in pistachios, is a more effective way to prevent heart disease than reducing overall fat intake, said Cooper.