Polar bears eat a diet high in fat -- incredibly high -- and yet mange to escape the risk of clogged arteries and heart attacks, researchers say, and it's all down to evolution and genetics.
Since they diverged from the lineage of brown bears just 500,000 years ago, becoming a new species, they've undergone radical changes and mutations of a number of genes involved in heart and circulation functions, the researchers say.
It's allowed them to consume the fat-laden diet they need to generate the energy required for survival in the extreme cold of Arctic regions but without the attendant risks of heart disease, say researchers who decoded the genome of bears from of tissue and blood samples of polar bears in Greenland.
The genetic data shows polar bears became a new species considerably more recently than was previously believed, around 500,000 years in the past rather than the five million years once thought.
"In this short amount of time, polar bears have adapted to the cold environment of the Arctic and to a new diet," University of California, Berkeley, evolutional geneticist Rasmus Nielsen says. "We see the footprints of this adaptation in the genome of the polar bear."
The bears have lots of fatty tissue as a result of their diet, a key to their survival.
As much as half their body weight is fat, and their main source of fresh water critical to their survival is metabolic water created as a byproduct of the breaking down of their body fat.
That's crucial because fresh water is hard to come by in Arctic environments, even though the bears are surrounded by snow and ice.
"They essentially live in a polar desert," Berkeley molecular ecologists Eline Lorenzen says.
The diet of polar bears consists mostly of blubber-rich seals, and polar bears' milk with which they nurse cubs is almost one-third fat.
"The life of a polar bear revolves around fat," Lorenzen says, and it's what let's them survive in their harsh surroundings.
"For polar bears, profound obesity is a benign state," she says.
That might not help the bears when it comes to climate change, unfortunately. Shrinking of sea ice that the bears depend on for getting around in their hunt for food has led to them becoming endangered, with an estimated total population of less than 25,000.
