Friday, September 18, 2015

The traditional diet of Greenland natives - the Inuit (once known as Eskimos) - is held up as an example of how high levels of omega-3 fatty acids can counterbalance the bad health effects of a high-fat diet, but a new study hints that what's true for the Inuit may not be true for everyone else

The study shows that the Inuit and their Siberian ancestors have special mutations in genes involved in fat metabolism that help them partly counteract the effects of a diet high in marine mammal fat, mostly from seals and whales that eat fish with high levels of omega-3 polyunsaturated fatty acids. Those genetic mutations, found in nearly 100% of the Inuit, are found in a mere 2% of Europeans and 15% of Han Chinese, which means that they would synthesize omega-3 polyunsaturated fatty acids differently from the Inuit. "The original focus on fish oil and omega-3s came from studies of Inuit: on their traditional diet, rich in fat from marine mammals, Inuit seemed quite healthy with a low incidence of cardiovascular disease, so fish oil must be protective," said project leader Rasmus Nielsen, a UC Berkeley professor of integrative biology. "We've now found that they have unique genetic adaptations to this diet, so you cannot extrapolate from them to other populations. It could be very good for the Inuit to eat all these omega-3 fatty acids, but not for the rest of us." These genetic mutations in the Inuit have more widespread effects. They lower "bad" LDL cholesterol and fasting insulin levels, presumably protecting against cardiovascular disease and diabetes. They also have a significant effect on height, because growth is in part regulated by a person's fatty acid profile. The researchers found that the mutations causing shorter height in the Inuit are also associated with shorter height in Europeans. "The mutations we found in the Inuit have profound physiological effects, changing the whole profile of fatty acids in the body, plus it reduces their height by 2 centimeters: nearly an inch," said Ida Moltke, a University of Copenhagen associate professor of bioinformatics who is joint first author on the study. "Height is controlled by many genes, but this mutation has one of the strongest effects on height ever found by geneticists." Nielsen noted that this is the first evidence that human populations are actually adapted to particular diets; that is, they differ in the way they physiologically respond to diets. Just as genome sequencing can lead to personalized medicine tailored to an individual's specific set of genes, so too may a person's genome dictate a personalized diet. "People ask themselves whether they should be on a stone-age diet, for example. The response may well depend on their genome," Nielsen said.

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