Polar bears adapted to subsist on high-fat diet

Why can polar bears gorge themselves on fat, grow exceptionally portly, and not have to worry about clogged veins and skyrocketing blood pressure like so many overweight Americans do? The short answer is: genetics. A new study of polar bear DNA undertaken by a team of international researchers -- including biologists from UC Berkeley -- has pinpointed a number of unique sections of genetic code that may explain how the mammal's metabolism and cardiovascular system remain unfazed by its huge fat intake. The scientists analysis featured blood and tissue samples from 79 Greenlandic polar bears and 10 brown bears from Sweden, Finland, as well as Alaska's Glacier National Park and ABC Islands. Whereas even the plumpest of Americans often excise the fatty portions of T-bone steak as they eat, adult polar bears subsist almost entirely on fat -- specifically the blubber of marine mammals. "The life of a polar bear revolves around fat," UC Berkeley researcher Eline Lorenzen explained. "Nursing cubs rely on milk that can be up to 30 percent fat and adults eat primarily blubber of marine mammal prey." Lorenzen also pointed out that polar bears develop large fat deposits under their skin, making them one of the fattest mammals on earth. Despite this, the bear's genes somehow help the predator's arteries avoid fatty plaque buildups -- keeping the Arctic beasts largely unaffected by the cardiovascular diseases that afflict so man humans. In conducting their DNA analysis, scientists also realized that polars bears, as a species, are much younger than previously thought. The genes, many of which help bears cope with their high-fat diet, that make polar bears unique, split off from brown bears on the evolutionary family tree only 500,000 years ago. "It's really surprising that the divergence time is so short," said Rasmus Nielsen, a professor of integrative biology at Berkeley. "All the unique adaptations polar bears have to the arctic environment must have evolved in a very short amount of time."