Carl Zimmer, New York Times, September 17, 2015
As the Inuit people spread across the Arctic, they developed one of the most extreme diets on Earth. They didn’t farm fruits, vegetables or grains. There weren’t many wild plants to forage, aside from the occasional patch of berries on the tundra.
For the most part, the Inuit ate what they could hunt, and they mostly hunted at sea, catching whales, seals and fish. Western scientists have long been fascinated by their distinctly un-Western diet. Despite eating so much fatty meat and fish, the Inuit didn’t have a lot of heart attacks.
In the 1970s, Danish researchers studying Inuit metabolism proposed that omega-3 fatty acids found in fish were protective. Those conclusions eventually led to the recommendation that Westerners eat more fish to help prevent heart disease and sent tens of millions scrambling for fish oil pills.
A study published last week in the journal Science reported that the ancestors of the Inuit evolved unique genetic adaptations for metabolizing omega-3s and other fatty acids. Those gene variants had drastic effects on Inuit bodies, reducing their heights and weights.
Rasmus Nielsen, a geneticist at the University of California, Berkeley, and an author of the new study, said that the discovery raised questions about whether omega-3 fats really were protective for everyone, despite decades of health advice. “The same diet may have different effects on different people,” he said.
The researchers found several genetic variants at different locations in the genome that were unusually common in the Inuit, compared with people in Europe or China. Several of these variations occurred within a cluster of genes that direct construction of enzymes called fatty acid desaturases. (The genes are called FADS, for short.)
Even more intriguing was the fact that one of these gene variants was present in almost every Inuit in the study. It is much less common in other populations: About a quarter of Chinese people have it, compared with just 2 percent of Europeans.
Natural selection is the only known way this gene variant could have become so common in the Inuit. Dr. Nielsen said this adaptation might have arisen as long ago as 20,000 years, when the ancestors of the Inuit were living in the Beringia region, which straddles Alaska and Siberia.
To uncover the effect of this variant gene, the scientists compared the Inuit in their study with others with more European ancestry. Some had inherited a European version of the variant. People with two copies of the Inuit gene had different blood levels of fatty acids than people without them, the researchers found.
The adaptation did more than just change blood levels of fatty acids, the scientists found. Inuit who carried two copies of the variant gene were on average an inch shorter and 10 pounds lighter than those without a copy.
“That’s quite extreme,” said Dr. Nielsen.
Indeed, it’s rare to find a single gene that can influence height and weight so drastically. In recent years, scientists have run a number of large studies pinpointing hundreds of genes that affect height and weight, but each one played a minuscule role in the variation from person to person.
Those studies missed this influential gene variant because they focused mostly on people of European ancestry. So Dr. Nielsen and his colleagues also investigated how it affects Europeans. As it turns out, the gene variant is linked to a drastic drop in height and weight in that population, too.