Fruit and vegetables are displayed at a grocer’s shop in London. (Christopher Furlong/Getty Images)
Why is it that some people can stay healthy only by sticking to a strict vegetarian diet? Why is it that others can eat a steak a day, remain slim, avoid heart disease and feel like a million dollars? The answers may lie in your heritage.
Cornell University researchers have found a fascinating genetic variation that they said appears to have evolved in populations that favored vegetarian diets over hundreds of generations. The geography of the vegetarian allele is vast and includes people from India, Africa and parts of East Asia who are known to have green diets even today.
Researcher Kaixiong Ye said that the vegetarian adaptation allows people to “efficiently process omega-3 and omega-6 fatty acids and convert them into compounds essential for early brain development.”
Omega-3 is found in fish, whole grains, olive oil, fruits and vegetables, while omega-6 is found in beef, pork products and many packaged snack foods such as cookies, candies, cakes and chips, as well as in nuts and vegetable oils.
Nutritionists believe that getting a good balance of these two types of fatty acids in the diet is essential to staying healthy. The body can’t produce these substances naturally, so it must get them from food.
Omega-3 is anti-inflammatory and helps regulate metabolism, which affects a wide range of functions in the body. In recent years, supplements rich in omega-3 have been trendy, based on the idea that it may reduce risk of heart disease. (The Food and Drug Administration says the evidence supports this theory but isn’t conclusive.) Omega-6 contributes to inflammation and plays an important role in skin and hair growth, bone health and reproductive health. Inflammatory responses are essential to our survival. They help fight off infections and protect us from injury. But if the response is excessive, it can lead to all kinds of problems and may contribute to a higher risk of heart disease, cancer and Alzheimer’s disease.
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Studies have suggested that humans evolved on a diet with a ratio of omega-6 to omega-3 essential fatty acids of 1:1 but that the Western diet has a ratio that is closer to 15 or 16:1. The Mediterranean diet, in contrast, is closer to having an equal balance of the two and is recommended by many doctors.
But this new study, funded by the National Institutes of Health and the U.S. Department of Agriculture, shows that different people may need radically different ratios of the substances in their diet depending on their genes, and it supports the growing evidence against a one-size-fits-all approach to nutrition and for highly personalized advice.
The existence of the vegetarian allele implies that, for people with this variation, straying from that diet — by eating a lot of red meat, for example — may make them more susceptible to inflammation, because their bodies were optimized for a different mix of inputs.
The research, published Wednesday in the journal Molecular Biology and Evolution, involved two parts. The scientists first analyzed the frequencies of the vegetarian allele in 234 primarily vegetarian Indians and 311 Americans living today. They found the vegetarian allele in 68 percent of the Indians and 18 percent of the Americans. Then they analyzed information from the 1,000 Genomes Project — a database of global DNA — to calculate an estimate of the frequency of the vegetarian allele in far-flung populations around the world. The differences were striking: 70 percent of South Asians, 53 percent of Africans, 29 percent of East Asians and 17 percent of Europeans had the gene variation.
The graph shows the global frequency pattern of an allele adaptive to vegetarian diets. The allele has the highest frequency in Indians, who have traditionally relied heavily on a plant-based diet. (Kaixiong Ye, Cornell University; map from www.outline-world-map.com)
Now here’s where their work gets even more interesting. Ye and colleagues found a different version of that gene adapted to a marine diet, rich in seafood, among the Inuit people in Greenland. Technically speaking, it’s the “opposite” of the vegetarian allele. The vegetarian allele has an insertion of 22 “bases,” or a building block of DNA, and this insertion was deleted in the marine allele.
Ye, who is the lead co-author along with Kumar Kothapalli, a senior research associate in nutritional sciences, theorized that having the vegetarian allele “might have been detrimental” for the Inuit because of their seafood-rich diets.
The vegetarian and marine alleles appear to control the FADS1 and FADS2 enzymes in the body, which are critical to converting omega-3 and omega-6 fatty acids into what the researchers called “downstream products” needed for brain development and controlling inflammation. People who eat meat and seafood need less of the FADS1 and FADS2 enzymes to get sufficient nutrition. “Their omega-3 and omega-6 fatty acid conversion process is simpler and requires fewer steps,” they noted.
Another groundbreaking study about genes and food was published in 2014 in Nature Communications. It found that a higher percentage of people in Europe — and particularly in Ireland — have variants for being lactose-tolerant, or able to break down the sugar in non-human milk.
[Ancient Europeans were lactose intolerant for the first 4,000 years they made cheese]
The authors said this ability appears to have evolved from a long history of milk drinking.
Ye explained that people with this kind of gene “absorbed enough end products from milk for long-chain fatty acid metabolism so they don’t have to increase capacity to synthesize those fatty acids from precursors.”
There has been considerable debate and research on when — and why — these types of variants cropped up.
In the case of lactose tolerance, early research had estimated that it arose 7,000 or more years ago, when people in the region began making cheese. But the Nature study wasn’t able to find it until 3,000 years back, which may imply that the populations had to rely heavily on dairy before the adaptation occurred.
Ye said the evolution of the vegetarian allele is less clear. It doesn’t exist in our ape relatives the chimpanzee or orangutan, but there is some evidence it may have been there in early hominids Neanderthal and Denisovan. It seems likely, the researchers wrote, that it has to do with migration patterns and the pressures that came with the availability or lack of availability of different kinds of foods in certain environments.
Today, in a world where many people have ready access to a wide variety of foods at their local groceries, the adaptations can act more as limitations to the kinds of foods you can eat to remain healthy.