By Jennifer Corbett Dooren, Wall Street Journal

Patients with heart disease frequently assume that medication is enough to forestall a repeat heart attack or stroke, but a large new study shows the preventive power of a healthy diet.

The findings from a report released last week looked at the impact of diet in addition to the medicines routinely used to treat cardiovascular disease. Although it is widely accepted that healthy diets are powerful tools to prevent cardiovascular disease, less is known about the impact of diet on people who already have the disease.

People with the healthiest diets — those with the highest intakes of fruit, vegetables, whole grains, nuts, and a higher intake of fish relative to meat poultry and eggs — were 35 percent less likely to die from a repeat heart attack or stroke during the length of the study, compared with those with the least healthy diets, according to the five-year study of 32,000 people in 40 countries.

They also were 28 percent less likely to develop congestive heart failure, 14 percent less likely to have an additional heart attack and 19 percent less likely to have a stroke.

Patients in the new study, published in the American Heart Association’s medical journal Circulation, previously participated in two studies designed to look at certain medicines used to treat high blood pressure.

“At times, patients don’t think they need to follow a healthy diet, since their medications have already lowered their blood pressure and cholesterol—that is wrong,” said Mahshid Dehghan, a study author and a nutritionist at the Population Health Research Institute, McMaster University in Hamilton, Ontario. “The more healthy you eat, the healthier you are.”

The drug and diet studies were funded by the German pharmaceutical company Boehringer Ingelheim.

Study participants were at least age 55 or older and had a prior history of heart disease, stroke or had Type 2 diabetes that was severe enough to have damaged organs.

The goal of the diet research was to see whether healthier diets had any impact on the rate of cardiovascular events such as heart attacks and strokes.

Participants in the diet-portion of the studies were followed for almost five years.

Dehghan explained that researchers used two diet indexes to measure diet quality and to rank people into five groups according to the healthiest to least-healthy diet.

People were asked how often they consumed dairy, meat, fish, fruits and vegetables. They were also asked about consumption of fried foods and whole grains. Portion sizes weren’t recorded.

Researchers controlled for other factors that can influence the progression of cardiovascular disease such as weight, exercise and smoking.

However, Steven Nissen, chairman of the cardiovascular medicine department at the Cleveland Clinic, said that while eating healthy is a good idea, the study itself “doesn’t prove anything.” Nissen said people with the healthiest diets are more likely to practice other healthy habits such as exercise and said the study authors “cannot adjust for all of these other known and unknown behaviors.”

Dehghan said researchers also looked at diet quality and the risk for other things, such as cancer, fractures and non-heart related hospitalizations and didn’t find any associations related to diet.

Heart disease is the top killer of Americans, according to the American Heart Association.

The group considers a heart-healthy diet to include more than four cups of fruits and vegetables, and at least three servings of whole grains daily, in addition to limiting intake of sodium and sugar-sweetened beverages.

At least two servings of fish and four servings of nuts or seeds are recommended each week, along with limiting processed meat to no more than two servings a week.