NEW YORK • As the Inuit people spread across the Arctic, they developed one of the most extreme diets on Earth. They did not farm fruits, vegetables or grains. There were not 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. Despite eating so much fatty meat and fish, the Inuit did not 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. Today, at least 10 per cent of Americans regularly take fish oil supplements. But recent trials have failed to confirm that the pills prevent heart attacks or stroke. And now the story has an intriguing new twist.
A study published in the journal Science reported that the ancestors of the Inuit evolved unique genetic adaptations for metabolising omega-3s and other fatty acids. Those gene variants had drastic effects on the Inuit's bodies, reducing their height and weight.
Dr Rasmus Nielsen, a geneticist at the University of California, Berkeley, and an author of the new study, said 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.
When humans encounter a new kind of food, natural selection may well favour those of us with genetic mutations that help us thrive on it. Some people, for example, are able to digest milk throughout their lives. This genetic adaptation arose in societies that domesticated cattle thousands of years ago, in such places as Northern Europe and East Africa. People who trace their ancestry to other regions, by contrast, more often tend to be lactose-intolerant.
Dr Nielsen wondered if the Inuit had a similar evolutionary change when they shifted to a diet made up mainly of meat.
The scientists selected 191 Greenlanders whose ancestry was 95 per cent Inuit or greater. They looked at the DNA of these people for variations in genes important to metabolism and found several genetic variants at different locations in the genome that were unusually common in the Inuit, compared with people in Europe or China.
This discovery was particularly tantalising, because the scientists knew that these enzymes helped regulate the different fats in our bodies, including omega-3 fatty acids.
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 per cent 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.
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 from people without them, the researchers found. "It seems that a genetic adaptation has counteracted the high intake of omega-3 fatty acids," said Dr Marit Jorgensen, an author of the new study from the University of South Denmark.
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 2.5cm shorter and 4.5kg lighter than those without a copy. "That's quite extreme," said Dr Nielsen.
He and his colleague are planning to investigate the long-term health effects of the gene variants they have found. They may help explain why some of us metabolise fats more effectively than others, and why omega-3s have not been the heart panacea once hoped.
NEW YORK TIMES
