People are motivated to try a vegetarian diet for different reasons – from ethical and religious, to potential health and environmental benefits. But many people have a hard time sticking with it. In fact studies show many self-reported vegetarians actually do consume some animal products.
"A lot of people who want to be vegetarian are perhaps not able to," says Dr. Nabeel Yaseen, of Northwestern University Feinberg School of Medicine. "We wanted to know if genetics is part of the reason," he says.
Yaseen and his collaborators compared the DNA of about 330,000 people, using data from the UK Biobank initiative. The study included 5,324 vegetarians, who had not eaten any animal flesh or products derived from animal flesh for at least one year.
They found 34 genes that may play a role in adhering to a strict vegetarian diet. And they identified 3 genes that are more tightly linked to the trait.
"What we can say is that these genes have something to do with vegetarianism," Yaseen says. "Perhaps vegetarians have different variants of these genes that make them able to pursue a strict vegetarian diet," he explains. The study is published in PLOS ONE, a peer-reviewed science journal.
Deciphering the genetic role is not exactly an easy riddle to solve. Humans have thousands of genes and there are millions of tiny variations in DNA building blocks, known as single nucleotide polymorphisms (SNPs,) where you can see differences between individuals.
To identify SNPs that are statistically associated with the particular trait of adhering to a vegetarian diet, Yaseen and his colleagues did a genome-wide association study.
"You're looking for markers in the genome, basically trying to see if a certain trait tracks with a certain region of the genome," explains Yaseen. When they found a SNP associated with vegetarianism, they looked to see the genes around it in the same area.
Of the three genes most strongly associated with vegetarianism, the authors say two of them (known as NPC1 and RMC1) have important functions in lipid – or fat – metabolism. The study can't answer exactly how genetic differences could shape or influence vegetarians, but Dr. Yaseen has some ideas.
"One hypothesis – which is highly speculative – is that maybe there's a lipid nutrient, or nutrients, in meat that some people need and others don't," he says.
Lots of factors influence what we eat, everything from our taste preferences, to our budgets to our culture. So, the idea that food choice is also influenced by genetics is not surprising, Yaseen says.
But this is just the first step. He says more research is needed to determine which genes – and which variants – may be critical.
Yaseen points out the current study is limited to white Caucasian participants. "Ethnicity is a confounding factor," he says. For example, if the study had included people from India, where vegetarianism is more common, you might see genes or SNPs that are associated with being Indian rather than being a vegetarian.
The idea that some people might find it easier to follow a vegetarian diet due to genetic predisposition is interesting, says Christopher Gardner, a food scientist at Stanford University. And he points out that people don't need to go completely vegetarian to see benefits.
He points to research that shows impacts on human health and planetary health would be significant, even if people just decreased the amount of meat they eat each week.
"There is clearly an important benefit – and probably more realistic benefit – of reducing meat without cutting it out completely," Gardner says.
This story was edited by Jane Greenhalgh
