Folks tend to think that decisions to become vegetarian are based on certain values and lifestyle choices that may take into account one’s religion or culture or even environmental concerns. But a new study in the journal PLOS One suggests genetics may play a bigger role than willpower in how successfully one forgoes meat.

A lot of research suggests that diet preference can be inherited to some degree and a team led by Northwestern University wondered if genes contribute to not just the desire for but also success at maintaining a vegetarian diet. To find out, they turned to the UK Biobank, comparing 5,324 strict vegetarians to 329,455 others to look for genes that might contribute.

A news release on the study from Northwestern Medicine notes that somewhere between half and two-thirds of people who call themselves vegetarians say they eat fish, poultry and /or red meat, which to corresponding study author Dr. Nabeel Yaseen, a professor emeritus of pathology at the university’s Feinberg School of Medicine, suggests that there are environmental or biological barriers to maintaining a strict vegetarian diet.

“It seems there are more people who would like to be vegetarian than actually are, and we think it’s because there is something hard-wired here that people may be missing,” he said in the release.

In the study’s abstract, researchers said it was already known that “dietary choices involve an interplay between the physiological effects of dietary items, their metabolism and taste perception, all of which are strongly influenced by genetics.”

They found 34 genes that might play a role in vegetarianism — and three of those proved significant in the genome-wide association study.

Several have important functions in fat metabolism and brain function, they wrote, noting it’s possible that differences in how people metabolize fat and the effect on their brain may determine if folks can sustain a vegetarian diet.

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About the study

The UK Biobank is a health resource that collects data — including questionnaire answers and also blood, urine and saliva, as well as health and demographic information — on 500,000 people ages 40-69 at the time they are recruited. Participant data is screened for relevance to different studies.

In this study, participants were those who did not consume any animal flesh — including beef, lamb, pork, poultry, fish or seafood and products like lard that come from animals within at least one year.

All were white “to attain a homogenous sample and avoid confounding by ethnicity.”

The researchers found significant differences between subjects and controls on several measures. Vegetarians were more likely to be women, younger in age, have a lower body mass index and have a lower socioeconomic status, according to the study.

While meat substitutes have grown in popularity, Northwestern reported that vegetarians are a small portion of the world population. “For example, in the U.S., vegetarians comprise approximately 3% to 4% of the population. In the U.K., 2.3% of adults and 1.9% of children are vegetarian,” the release said.

Nature and nurture intertwined?

NBC News notes the role comparing twins has played in past research on dietary preference.

Dr. Laura Wesseldijk, lead author of one such twin study, told NBC that one of her studies published in January suggests genes “account for 70% to 80% of individual differences in abstinence from eating beef, pork, poultry, fish and shellfish.”

Wesseldijk, a behavioral geneticist at Amsterdam University Medical Centers who wasn’t part of the Northwestern-led research, added that no human traits are entirely nature or nurture. Instead, “it’s all completely entangled,” she told NBC. “... An environment can completely counteract something that is highly heritable, and the same goes with vegetarianism,” she said, per NBC.

“While religious and moral considerations certainly play a major role in the motivation to adopt a vegetarian diet, our data suggest that the ability to adhere to such a diet is constrained by genetics,” Yaseen said. “We hope that future studies will lead to a better understanding of the physiologic differences between vegetarians and non-vegetarians, thus enabling us to provide personalized dietary recommendations and to produce better meat substitutes.”

Yaseen told NPR that one very speculative theory “ is that maybe there’s a lipid nutrient, or nutrients, in meat that some people need and others don’t.”