People may turn to vegetarian diets to reduce their risk of heart disease, but a new study suggests not all plant-based foods are created equal.

People on plant-based diets who consume lots of refined grains and sweets may be significantly more likely to develop heart disease than vegetarians whose diets include the least amount of these types of foods, the study suggests.

"Most studies that examine vegetarian diets found them generally to be protective of cardiovascular disease, but they didn’t really look at the quality of plant food," said lead author Ambika Satija, of the Harvard T.H. Chan School of Public Health in Boston. "It’s possible to be a vegetarian and eat low-quality plant food."

As reported in the Journal of the American College of Cardiology, Satija and colleagues analyzed data from three past studies that asked people about their diets every few years and included information on how many developed heart disease.

The three studies included a total of 210,298 people. Over about 20 years, 8,631 participants developed coronary heart disease due to plaque build-up in the arteries that carry blood to the heart. The condition can lead to chest pain, heart attacks and other health issues.

The researchers divided participants into 10 groups according to how closely they adhered to a plant-based diet. People whose diets were the most plant-based had an 8 percent lower risk of heart disease than those whose diets were the least plant-based - but that finding could have been due to chance.

Next, they compared groups of people whose diets included the most healthy plant-based foods like whole grains, fruits, vegetables and nuts, versus people whose diets contained the least amount of those foods. Those with the healthiest plant-based diets were 25 percent less likely to end up with heart disease than those with the least-healthy plant-based diets.

Similarly, those whose diets included the most unhealthy plant-based foods (refined grains, sugary beverages, potatoes and sweets) were 32 percent more likely to develop heart disease, compared to those whose plant-based diets included the least amount of those unhealthy options.

People who eat unhealthy plant foods "could consider changing their diet and switching out the less healthy plant foods for healthy plant based foods," Satija told Reuters Health.

She also said modestly lowering the amount of animal foods in a person's diet was linked to a decreased risk of heart disease.

"Make small changes and you might be able to benefit," said Satija.

In an editorial accompanying the new study, Drs. Kim Allan Williams and Hena Patel, of the Rush University Medical Center in Chicago, say healthy plant-based diets can play an important role in preventing cardiovascular disease.

"Such diets, which have many other health benefits including the prevention of several chronic diseases, deserve more emphasis in dietary recommendations," they write.

The conclusions of the new analysis may be correct, but the study doesn't prove it, said Dr. Steve Nissen, who is chair of the Robert and Suzanne Tomsich Department of Cardiovascular Medicine at the Cleveland Clinic in Ohio.

"There are so many confounding variables," said Nissen, who wasn't involved with the new study.

People may have misreported what they ate on their food questionnaires, for example, or there could be other factors that explain differences in outcomes like social and economic status, he said.

Nissen told Reuters Health that the best evidence on a diet to prevent heart disease is from the PREDIMED Study that supports a Mediterranean diet, which focuses on unrefined grains, legumes, nuts, fruits, vegetables, fish, moderate amounts of alcohol like red wine and a high amount of monounsaturated fats like olive oil.

"It's prospective, randomized and shows a large reduction in morbidity and mortality with a Mediterranean diet," said Nissen.

The American Heart Association recommends diets that include fruits and vegetables, nuts and legumes, whole grains, low-fat dairy products, non-tropical vegetable oils and skinless poultry and fish.

Source: Reuters