People’s likelihood of being vegetarian appears to be influenced by several genetic variants, and two of the three most important genes found so far seem to be involved in fat metabolism.
This hints that some people find it easier to give up meat because they naturally produce certain fat molecules, says Nabeel Yaseen at Northwestern University in Chicago. “Maybe there’s some fat that’s essential for some people to have in their diet but not for others,” he says.
About 5 per cent of people in the UK and US avoid all meat and fish. But surveys indicate that some people who say they are vegetarian still eat meat sometimes. That suggests that some people would like to be vegetarian but find it too hard, says Yaseen.
Genetic factors are known to influence other aspects of diet, such as whether people like coffee or alcohol. To see if genes also affect vegetarianism, Yaseen and his team turned to the UK Biobank, a large study where people filled in lifestyle and medical surveys and had their DNA sequenced. They analysed about 5300 people who said they were strict vegetarians and another 330,000 people who were meat eaters.
Three gene variants were more common in vegetarians. Two, called NPC1 and RMC1, are involved in the transport and metabolism of cholesterol and other fatty molecules called glycolipids. The third gene, called RIOK3, has various functions, including affecting the immune system.
It isn’t known exactly how these genes could relate to vegetarianism. But one of the chief differences between animal-based foods and plant-based ones is the chemical make-up of their fats or oils, collectively known as lipids. Yaseen and his colleagues speculate that some people may function better on a vegetarian diet because they are more able to synthesise certain lipid molecules that are present in meat.
People who try vegetarianism but give up may be doing so because the body becomes deficient in the postulated essential lipids, says Yaseen. “They decide that this diet is not for them or gradually creep back into an omnivore diet. Some people might think they just don’t have the willpower.”
Yaseen says, however, that another possibility is that the apparently vegetarianism-promoting gene variants affect people’s taste. “A lot of information about genes is yet to be known,” he says.
Albert Koulman at the University of Cambridge says most research into how food nutrients influence satiety and food choices has focused on proteins rather than fats. “We don’t know enough about [this idea] to either accept or dismiss it,” he says.
Richard McIlwain at the UK Vegetarian Society says the number of vegetarians has been rising in recent years, almost doubling in the UK between 2012 and 2019. “That would seem to suggest something other than underlying genetic factors are at play,” he says.
“People go vegetarian because, more and more, they are concerned about climate, about animal welfare or about their health. Psychological factors, such as tradition, education and awareness of animal suffering in food production, and ‘taste preferences’ are far more important determinants of vegetarianism than any physiological factors,” says McIlwain.