Healthy dieters reduced their risk factors for heart disease like weight and body fat equally when they followed a vegetarian diet that included eggs and dairy or with a Mediterranean diet that emphasised olive oil and lean fish, an Italian experiment found.

Researchers randomly assigned 107 overweight adults to follow either a vegetarian or Mediterranean diet for three months, then to switch to the other diet for three more months. At the start of the study, all of the participants were omnivores, meaning they ate both animals and plants.

People were not given particular weight loss goals, but they received regular counseling from nutritionists on how to reduce calories and suggested meals and menus were designed to be low-calorie. On both diets, participants were advised to consume 50 to 55 per cent of their calories from carbohydrates, 25 to 30 per cent from fats and 15 to 20 per cent from lean protein.

Participants lost similar amounts of body fat and weight - about 4 pounds - with each diet, researchers report in Circulation. The "lacto-ovo" vegetarian diet with was associated with bigger reductions in "bad" LDL cholesterol, however, and the Mediterranean diet was linked to larger decreases in triglycerides and markers of inflammation.

Each diet, separately, has been shown to produce to bigger improvements in weight and other risk factors for heart disease than a typical Western diet heavy on red meat, starch, processed foods and sugary drinks. But research to date has not offered a clear picture of how well a vegetarian diet stacks up against a Mediterranean diet, said lead study author Dr. Francesco Sofi, a nutrition researcher at the University of Florence and Careggi University Hospital.

"This is the first study that aimed to compare the two diets in the same groups of subjects who were omnivores," Sofi said by email.

"The take-home message is that a lacto-ovo vegetarian diet is easy and feasible to follow, without any health problems, if well conducted and prepared by an instructed nutritionist," Sofi added. "This helps you to reduce some cardiovascular risk factors as well as a Mediterranean diet."

A Mediterranean diet typically includes lots of fruits, vegetables, whole grains, legumes and olive oil. This diet also tends to favour lean sources of protein like chicken or fish over red meat, which contains more saturated fat.

Lacto-ovo vegetarians also eat fruits, vegetables and whole grains, as well as eggs and dairy, but avoid poultry, meat and fish.

Compared to their eating habits at the start of the study, people significantly cut back on calories, total fat and saturated fats with each diet in the experiment.

With the vegetarian diet, people did experience bigger reductions in low-density lipoprotein (LDL), the bad kind of cholesterol that can build up in blood vessels and lead to clots and heart attacks. That's to be expected because a lot of LDL in the body comes from eating meat, Sofi said.

The bigger reduction in triglycerides, or fatty acids, with the Mediterranean diet is also to be expected, Sofi said. That's because a combination of olive oil, and complex carbohydrates in fruits and vegetables that are a hallmark of this diet are known to reduce triglycerides.

While the study was a controlled experiment and offers solid evidence that both a vegetarian and Mediterranean diet can help lower certain risk factors for heart disease, the experiment wasn't designed to show why one diet might be better for cholesterol or triglycerides, noted Cheryl Anderson, author of an accompanying editorial and a researcher at the University of California San Diego School of Medicine.

"To my knowledge, this is the first randomized clinical trial comparing the effectiveness of a low-calorie vegetarian diet to a low-calorie Mediterranean diet," Anderson said. "It is novel that the study participants were relatively healthy, and at relatively low risk for cardiovascular disease."

These aren't the only diets that can promote heart health, however.

"Patients now have data to support multiple choices for types of diets they can follow for cardiovascular health promotion," Anderson said. "They can find sample menus for each type of diet at choosemyplate.gov."