The scientists hope that their findings, which are now published in the journal Circulation, might raise awareness that the vegetarian diet can offer another option for reducing the risk of heart disease and stroke.
The Mediterranean diet "is widely reported as one of the healthiest models for preventing cardiovascular disease," they note, whereas the vegetarian diet is much less well studied — particularly in regard to its potential to offer a heart-healthy alternative for people who are used to eating meat and fish.
"To best evaluate this issue," says lead study author Francesco Sofi, a professor of clinical nutrition at the University of Florence and Careggi University Hospital in Italy, "we decided to compare a lacto-ovo-vegetarian diet with a Mediterranean diet in the same group of people."
A lacto-ovo-vegetarian diet excludes meat, poultry, fish, seafood, and any foods that are derived from them, but it includes eggs and dairy products such as milk, yogurt, and cheese.
Both reduced 'cardiovascular risk profile'
For their study, Prof. Sofi and colleagues randomly assigned 107 participants to follow either a low-calorie vegetarian diet or a low-calorie Mediterranean diet for 3 months. The participants were aged between 18 and 75 and were all healthy but overweight.
The study was a crossover trial, which means that at the end of the first 3 months on one diet, the participants switched over to the other diet for another 3 months.
All of the participants attended counseling sessions, during which they received advice about the diet that they were about to start on. The information included a detailed menu plan for 1 week of meals, as well as information about foods to include and exclude.
Both of the diets were designed to be low-calorie and match the energy needs of the individuals. In both diets, around 50–55 percent of calorie intake was derived from carbohydrates, 15–20 percent from protein, and 25–30 percent from fat (with less than 7 percent from saturated fat and fewer than 200 milligrams per day of cholesterol).
There "were no substantial differences," note the authors, between the two diets in the number of servings per week of olive oil, fruits, vegetables, cereals, potatoes, and sweets.
Also, unsurprisingly, the groups reported eating more legumes, eggs, nuts, and dairy foods when they were on the vegetarian diet than when they were on the Mediterranean diet.
The results showed that both diets significantly improved participants' overall "cardiovascular risk profile," although they differed slightly in the detail.
Different impact on cholesterol, triglycerides
Regarding physical measures — such as body mass index (BMI) and body fat — the two diets were "equally effective." The participants lost an average of 4 pounds in body weight and 3 pounds of body fat.
But the diets differed in their impact on some of the biochemical risk factors for cardiovascular disease.
Following the vegetarian diet led to a significant reduction in low-density lipoprotein, or "bad," cholesterol. In contrast, following the Mediterranean diet seemed to be more effective at reducing levels of triglycerides.
Nevertheless, "the take-home message our study," says Prof. Sofi, "is that a low-calorie lacto-ovo-vegetarian diet can help patients reduce cardiovascular risk about the same as a low-calorie Mediterranean diet."
Both diets were 'consistent with guidelines'
In an accompanying editorial, Cheryl A. M. Anderson — who is an associate professor of preventive medicine at the University of California, San Diego — comments on the value of the study.
She points out that both the low-calorie vegetarian diet and low-calorie Mediterranean diet "are consistent" with guidelines and "may offer a possible solution to the ongoing challenges to prevent and manage obesity and cardiovascular diseases."
There is an urgent need to find more solutions to tackle the obesity epidemic. Worldwide, there are more than 650 million people with obesity — which is around three times as many as there were in 1975.
In the United States, obesity affects 37 percent of adults, and it is implicated in some of the leading causes of preventable deaths, including type 2 diabetes, heart disease, and some types of cancer.
A growing body of 'persuasive evidence'
The new study adds to a body of "persuasive evidence" that there are several dietary patterns that offer a healthful way to reduce weight and improve cardiovascular health, Prof. Anderson explains.
Also, she notes that such patterns "should include a few basic principles such as being nutrient dense; rich in vegetables and fruits, whole grains, legumes, and nuts; low in refined grains and commercially processed foods with added sugars, saturated fats, and sodium; sustainable; culturally relevant; and enjoyable."
Prof. Anderson suggests that there is a need for future studies to compare the effects of the two diets in populations with a higher heart disease risk.
These should also explore "whether or not healthful versions of traditional diets around the world that emphasize fresh foods and limit sugars, saturated fats, and sodium can prevent and manage obesity and cardiovascular diseases," she urges.
"People have more than one choice for a heart-healthy diet."
Prof. Francesco Sofi