Scientists say there is a “vegetarian gene” – but it appears to be linked to a greater risk of cancer and health problems.
People from countries with a history of eating plant-based diets have a genetic mutation which leaves them vulnerable to high inflammation.
The gene helps those who do not eat meat or fish to create additional fatty acids which are essential to the body.
But the side effect is that they react badly in the presence of cheap cooking oils such as sunflower oil, overloading the body with omega-6 compounds.
Scientists say this then blocks a series of internal processes that can result in dangerously high inflammation, colon cancer, and heart problems.
Professor Tom Brenna, from Cornell University, said that the advent of cheap cooking oils had meant the useful gene is now more of a hindrance than a help, causing the body to take up too much arachidonic acid – which causes the inflammation.
He said: “Those whose ancestry derives from vegetarians are more likely to carry genetics that more rapidly metabolise plant fatty acids.
“In such individuals, vegetable oils will be converted to the more pro-inflammatory arachidonic acid, increasing the risk for chronic inflammation that is implicated in the development of heart disease, and exacerbates cancer.
“The mutation appeared in the human genome long ago, and has been passed down through the human family.”
Researchers from Cornell University in New York compared the gene sequences of 234 Indians – where meat is eaten much less – and 311 Americans from Kansas, where meat is eaten regularly.
They found the gene mutation in 68% of the Indians, compared to just 18% of the people from Kansas.
Most of the Inuit – who eat lots of oily fish and seals that are rich in omega-6 and omega-3 – have no copies of the gene at all.
The study was published in the Molecular Biology and Evolution.