Why Polar Bears Are Fat, But Have Healthy Hearts

Polar bears appear to be genetically superior to humans when it comes to warding off heart disease, a new study on the hefty bears finds.

What's remarkable is that polar bears are among the most fat-obsessed beasts in the animal kingdom.

"The life of a polar bear revolves around fat," according to Eline Lorenzen of UC Berkeley who worked on the study. It's published in the latest issue of the journal Cell.

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"Nursing cubs rely on milk that can be up to 30 percent fat and adults eat primarily blubber of marine mammal prey," Lorenzen explained. "Polar bears have large fat deposits under their skin and, because they essentially live in a polar desert and don't have access to fresh water for most of the year, rely on metabolic water, which is a byproduct of the breakdown of fat."

Our culture is fat-phobic, valuing skinny people who ideally eat low-fat diets, so how is it that evolution has led to fat polar bears that eat mostly fat?

Lorenzen and her colleagues looked at the genomes of 79 polar bears from Greenland and 10 brown bears from different locations around the globe to answer that question and more.

They first determined that polar bears and brown bears diverged less than 500,000 years ago. That's incredible, considering that prior theories estimated the two species parted evolutionary ways up to 5 million years ago.

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"In this limited amount of time, polar bears became uniquely adapted to the extremities of life out on the Arctic sea ice, enabling them to inhabit some of the world's harshest climates and most inhospitable conditions," the study's senior author Rasmus Nielsen, also of UC Berkeley, said in a press release.

Up to half of the body weight of polar bears consists of fat, and their blood cholesterol levels are high enough to cause cardiovascular disease in humans.

Nielsen and his team, however, discovered that mutations in genes involved in cardiovascular function allowed polar bears to rapidly evolve the ability to consume a fatty diet without developing high rates of heart disease. One such gene, called APOB, is known to play a role in moving cholesterol from the bloodstream into cells, thus reducing the risk of heart disease.

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"Such a drastic genetic response to chronically elevated levels of fat and cholesterol in the diet has not previously been reported," co-author Eske Willerslev of the University of Copenhagen said. "It certainly encourages a move beyond the standard model organisms in our search for the underlying genetic causes of human cardiovascular diseases."

Polar bears might therefore hold the genetic key to humans avoiding heart disease. Hopefully these majestic animals will still be around for us to benefit - and admire.

Heart attacks aren't doing them in, but declining habitat due to disappearing Arctic sea ice is. It's estimated that the worldwide population of polar bears is only about 20,000 to 25,000.

Photo: Polar bear on Kap Tobin, Scoresby Sound, Central East Greenland. Credit: Rune Dietz, Aarhus University.

Event: 200m Race

July 30, 2012

- Over the next few weeks, until August 12, the world’s best Summer Olympic athletes will display their sporting skills. But non-humans could also ace many events. Cheetahs, for example, can run up to 70 miles an hour. The cheetah in this photo, chasing a Thompson’s gazelle in Tanzania, could very well have been going that speed. In a nod to super-fast species, two cheetah cubs, a male and a female, at the Smithsonian's National Zoo will soon be named after the fastest American male and female in the Olympics 100-meter dash. The possible names for the female cub: Carmelita, Tianna and Allyson; for the male cub: Justin, Tyson and Ryan.

NEWS: Robotic Cheetah Could Catch Usain Bolt

Event: Sailing Sailfish can swim up to 68 miles per hour, which would allow them to zip through the Olympics sailing event even without a sailboat! The fish actually has a "sail" that is normally kept folded down and to the side when swimming, but can be raised at any moment. Fish, sharks and marine mammals are such talented swimmers that Olympic athletes study their movements and wear suits modeled after their body structures. Rajat Mittal, a professor in the Whiting School of Engineering at Johns Hopkins University, has worked with Olympic athletes, providing information about swimming mechanics inspired by dolphins. He told Discovery News, “To win, our Olympians must go all out and swim in what is essentially an efficient manner. Dolphins and sharks, by contrast, never compromise their speed with efficiency. They are truly among nature’s best swimmers.”

VIDEO: Watch Sailfish in Action in this LIFE clip.

Event: Soccer Woe be the soccer player who comes into contact with a North African ostrich. These flightless birds, weighing in at around 345 pounds, can kick humans to death. They are also the fastest bird on land, running up to 45 miles per hour. If birds could play field sports a la Harry Potter, taking to the air, Peregrine falcons would be the team choice. They can dive toward the earth at speeds greater than 200 miles per hour.

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Event: Weightlifting Rhinoceros beetles can lift 850 times their own weight. Pound for pound, they would blow away all other insect and animal contenders.

VIDEO: Watch a Rhino Beetle Put to the Test

Event: 400m Freestyle Swimming Dall porpoises can swim up to 35 miles per hour, making them the fastest water-dwelling mammals, according to the Smithsonian's National Zoo. Russell Mark, USA Swimming's director of biomechanics, told Discovery News that the dolphin/porpoise-style kick can make or break most human swimming races. "This is when swimmers push off walls and swim underwater without moving their arms," he explained.

VIDEO: Meet Winter the Dolphin and Her Prosthetic Tail

Event: Equestrian They may not be pretty, but parasitic horse flies could outlast any human rider during equestrian events. These parasitic flies sink their knife-like mandibles into horses and other animals in order to drink blood.

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Event: Long jump Tiny crustaceans called copepods were recently named the world’s best animal jumpers. They leap with greater muscle power than kangaroos, frogs and all other impressive animal jumpers. According to Thomas Kiorboe, a professor in the Oceanography Section at the Technical University of Denmark’s National Institute for Aquatic Resources, copepods can accelerate to 500 body lengths per second when they perform an escape jump away from countless underwater predators. "The trick is that copepods, unlike most other animals, have two different propulsion systems: one for swimming and one for jumping," Kiorboe explained to Discovery News.

VIDEO: See a copepod perform its medaling jumps!

Event: Wrestling Human wrestlers would be squashed in minutes if they dared to take on a polar bear in wrestling. Polar bears, which can weigh up to 1,500 pounds, are good at this activity too, since play-fighting is common among males. Actual fighting, which takes place during the mating season, can become intense, often resulting in scars and broken teeth.

VIDEO: Global Warming is Affecting Polar Bears: See How

Event: Fencing Like sword-wielding fencers, lobsters often use their claws to fight with each other. That's one reason why the claws of lobsters are rubber-banded closed in fish market tanks.

BLOG: Are lobsters getting more colorful?

Event: Shooting Skunks don't shoot bullets, but they can shoot their unbelievably smelly spray up to 15 feet. Even if that didn't beat the distance of a human shooter, the skunk could probably win anyway, by quickly emptying the field.

WIDE ANGLE: Follow the Olympics with Discovery News!