Vegetarians are assumed to be healthier than carnivores, but a new study questions that assumption. It found meat eaters had no significantly greater risk of heart disease over 10 years compared to those who favoured no-meat diets.
"I wouldn't say a vegetarian diet is useless for preventing cardiovascular risk," said study leader Dr Hyunseok Kim.
However, the heart benefits on a population level may be less than some believe, said Kim, an internal medicine resident at Rutgers New Jersey School of Medicine in Newark.
The study findings puzzled one nutritionist who said previous research has indicated that a vegetarian diet is good for the heart.
Read: Heart health predicts brain health
The study used US national survey data to compare adult vegetarians to thousands of meat eaters. While vegetarians were thinner, their overall heart risk wasn't actually different, according to the study.
"Followers of the vegetarian diet do have lower risks of obesity, high blood pressure and metabolic syndrome," all risk factors for heart disease, Kim said. But that may be partly because vegetarians are often younger and female, so they're already at lower risk for heart disease, the study said.
Kim and his Rutgers colleagues used the U. National Health and Nutrition Examination Survey from 2007 to 2010. It included nearly 12,000 adults age 20 or older. Of those, 263 – 2.3 percent – followed a vegetarian diet.
A cluster of conditions
The researchers examined rates of obesity, average waist circumference, high blood pressure and metabolic syndrome – a cluster of conditions, including high cholesterol and glucose levels – that raise the risk for heart disease.
They also assessed the Framingham cardiovascular-disease risk estimate, which factors in age, gender, cholesterol levels, blood pressure and smoking status to predict the chances of developing cardiovascular disease in the next decade.
Read: Cardiovascular disease linked to Metabolic Syndrome
When the researchers calculated the participants' Framingham risk, the vegetarians had a risk of 2.7 percent, while the non-vegetarians had a 4.5 percent risk. The difference between the groups was not statistically significant, Kim said.
The findings surprised one nutrition expert.
"We would certainly consider this study as we look for more data on the health benefits of vegetarian diets, but this study is contrary to evidence provided in the 2015 Dietary Guidelines for Americans and in a position paper of the Academy of Nutrition and Dietetics," said Connie Diekman. She's the director of university nutrition at Washington University in St. Louis.
'A snapshot in time'
Under those guidelines, "consuming more fruits and vegetables is connected with a lower risk of cardiovascular disease," Diekman said. Eating more whole grains is also thought to lower the risk, she noted.
"The Academy position states that a vegetarian diet is associated with a lower risk of death from ischaemic heart disease," added Diekman, who wasn't involved in the study.
She said she encourages people to adopt a diet "that more closely resembles a vegetarian eating plan".
Read: Is my vegetarian diet balanced?
The study is cross-sectional, sort of a snapshot in time, Kim said, so that is one inherent limitation. Another is that people self-reported their diet.
Studies that follow people over time are needed to better assess the benefits of vegetarian diets, Kim added.
Kim presented the findings at an American College of Gastroenterology meeting in Las Vegas. Research presented at medical meetings is viewed as preliminary until published in a peer-reviewed journal. The study had no outside funding and no industry funding.
10 interesting vegetarian facts
The healthy vegetarian diet
Heart disease – the facts