April 26, 2016

Healthiness of a Vegetarian Diet May Depend on Genetic Disposition

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You might want to be careful if you’re trying to switch to a vegetarian diet. According to a recent study, published in Molecular Biology and Evolution, your genes could play an important role in deciding whether a plant based diet is good for you.

Fatty acids such as omega-3 and omega-6 are crucial to brain and immune system development and function. While red meats and seafood are full of these nutrients, plants are not. Veggies contain the necessary precursors for the production of fatty acids, but not the final product. Individuals with a vegetarian diet, then, can struggle to acquire a sufficient amount of the omega-6 and omega – 3 fatty acids.

Kaixong Ye, postdoc, one of the lead authors of the paper and a member of Keinan Lab, collaborated with Prof. Tom Brenna, nutritional sciences, whose research pinpointed a mutation that affects the breaking down of fatty acid. The mutation is typically found in a large supply in meat and seafood and is responsible for the extraction of necessary nutrients from plants.

The study also found that while many individuals of European descent lacked the veggie-processing allele the majority of South Asians do not. In fact, around 70 percent of South Asian have not one, but two copies of the necessary allele for plant-based extraction of the necessary nutrients often found within fatty acids.

“With their study [Brenna’s study on mutation], there were several possible explanations for why the insertion was more common in Indians; it could be, for instance, purely random,” Ye said. “Our expertise is that we were able to distinguish many possible explanations for the higher frequency of the allele in particular populations.”

So, to try and discern the reasoning behind the variation, Ye and his fellow authors used the 1000 Genomes Project database. With the fully sequenced genomes of about 2,500 individuals from 26 different populations on file, the research crew was able to take a closer look at the presence of the vegetarian allele in various populations around the globe.

“We looked at the region with the insertion in question and ran a bunch of statistical analyses on it,” Ye said. “What we found is that in India, the reason there is such a high frequency of this insertion is because of local adaptation.”

In many ways, it is basic evolution: many thousands of years ago, as Indians slowly adopted a vegetarian diet, those individuals with the insertion were healthier and were able to have more offspring. As such, the proportion of individuals with the allele grew.

In further support of their conclusions, Ye and his team discovered something fascinating and unexpected when searching for the vegetarian allele amongst the Greenlandic Inuit. Subsisting on a diet almost completely without vegetables, the Inuit in Greenland would have little need for the vegetarian allele; and indeed, their population was found to be nearly completely absent it.

“It is as if nature did some experiment for us; several thousand years ago, there was a group of individuals — some of them had the vegetarian allele, some did not. Some were placed in India, some in Greenland, which are places with different diets. Over the next several thousand years the Indian population — along with some African populations and some East Asian populations — because of their vegetarian diets, saw an increase in frequency of the vegetarian allele. For the Greenlandic Inuit, they had a different diet, and overtime the vegetarian allele was removed from their population,” Ye eagerly illustrated.

The story of the Greenland Inuit was probably the discovery that most surprised the research team, Ye said. With the vegetarian allele missing in their population, he said “the other allele underwent positive selection amongst the Inuit.”

“This is something quite uncommon during human evolution, that one allele is adaptive in one environment and maladaptive in another,” he said. “To my knowledge, I am not aware of any other study showing this sort of phenomenon.”

Since Ye and his research team demonstrated that there is indeed an evolutionary component to individuals’ ability to extract important fatty-acid nutrients from vegetables, many in the media hopped to with dire warnings about the unhealthy nature of vegetarian diets. However, Ye clarified that the study says nothing about whether a vegetarian diet is good or bad.

“The major take-away message of our study is that the diet that is right for you depends on your genetic background,” he said, “[If Europeans] rely purely on a plant-based diet it may not be sufficient for them since most Europeans lack the vegetarian allele.”

Much of it, he pointed out, is about omega-3 and omega-6. Ideally, we would maintain a dietary ratio of one to one, with anything at or under four to one (omega – 6 to omega – 3) sufficient for our health. By eating too much meat and seafood, those with the vegetarian allele are ingesting extraneous amounts of omega-6, since they already derive quite a bit from vegetables. On the flipside, those without the allele require more meat and seafood — and yes, oils — to maintain a proper amount of fatty acids; and since they are unable to extract those nutrients from greens, a purely vegetarian diet probably will not do the trick.

Ye sees much room for such, and even more, precise dietary advice in the future.

“The key point [of our study] is that there is no one diet that is good for all people, and now, the idea in nutrition and human health research is that we need precision medicine and a personalized nutrition,” he said. “Now, we have the capacity to do it. We can do a sequencing and ask, do you have the vegetarian allele?”

What advice does Ye foresee nutritionist giving those with the allele?

“If you have the vegetarian allele, stick to the traditional vegetarian diet; if you eat a lot of meat and seafood something bad could happen,” he said. “We aren’t exactly sure what, but our argument is, look at the Greenlandic Inuit — those that had the vegetarian allele are gone.”

He Ye discerns a bright future ahead for nutrition.

“Each person can get their genome sequenced just once in their lifetime, and then have all of their genetic information. Theoretically, we can make inferences based on this information as to what sort of diet is best for us and what sort of lifestyle we need to adapt in order to lead a healthy life,” he said. “I think that’s the future.”

Still, Ye admits work remains to be done.

“We know the mutations, but we first need to connect those mutations to the trait. And our study is just one example of this type of research.”