Researchers have found a genetic variant in populations that have favoured vegetarian diets over many generations.
The adaptation, seen in Indian and East African populations, appears to have evolved to allow people to more efficiently convert omega-3 and omega-6 fatty acids from a plant-based diet. The researchers found the 'opposite' mutation among Inuit people, who eat largely seafood-based diet.
'Our study is the first to connect an insertion allele with vegetarian diets, and the deletion allele with a marine diet,' said Kaixiong Ye, a graduate student at Cornell University and co-author of the study, which was published in Molecular Biology and Evolution.
The researchers obtained blood samples from 234 primarily vegetarian Indians and 311 Americans. They found the allele – an inserted stretch of 22 base-pairs – in 68 percent of Indians compared with 18 percent of Americans. They then examined the data from the 1000 Genomes Project and found the vegetarian allele in 70 percent of South Asians, 53 percent of Africans, 29 percent of East Asians and 17 percent of Europeans.
The populations with the highest frequency of this allele are ones which have traditionally eaten a vegetarian diet over many generations. By contrast, they found that the same stretch of DNA was deleted in the Inuit population. 'The opposite allele is likely driving adaptation in the Inuit population,' said Ye.
The study focused on FADS1 and FADS2 genes, which code for enzymes involved in the conversion of the polyunsaturated fatty acids (PUFAs) omega-3 and omega-6 into compounds essential for early brain development and for controlling inflammation. Meat and seafood eaters have less need for increased FADS1 and FADS2 enzymes because their omega-3 and omega-6 fatty acid conversion process is simpler and requires fewer steps.
'Northern Europeans have a long history of drinking milk and they absorbed enough end products from milk for long-chain fatty acid metabolism so they don't have to increase capacity to synthesise those fatty acids from precursors,' said Ye. 'One implication from our study is that we can use this genomic information to try to tailor our diet so it is matched to our genome, which is called personalised nutrition.'
It is not clear when the adaptation first occurred, and analyses of chimpanzee or orangutan genomes did not uncover the vegetarian allele. But there is evidence for the allele in early hominid Neanderthal and Denisovan genomes.
'It is possible that in the history of human evolution, when people migrated to different environments, sometimes they ate a plant-based diet and sometimes they ate a marine-based diet, and in different time periods these different alleles were adaptive,' said Ye.