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Fat Bears

February 12, 2015

Grizzly bears pile on the fat every autumn. But in their obese state through hibernation, they don’t appear to suffer health consequences like overweight humans do. Scientists in eastern Washington are trying to figure out why. A new study involving those bears may yield insights into possible therapies for human obesity and diabetes.

Michael Werner: Plump. Pudgy. Portly. Call them what you will, but for grizzlies, being fat is being happy.

Heiko Jansen, Associate Professor, Washington State University: They’re sort of OCD eaters in the fall. They will consume so much of that that they're putting on nearly 10 pounds a day. If you translate that to pizzas, it’s about 16 large pepperoni pizzas a day.

Before hibernating, grizzly bears can put on 10 pounds a day.

Werner: For humans, this kind of weight gain could cause some serious health problems like heart disease, stroke and type 2 diabetes. But grizzlies have trouble surviving without it.

Jansen:  All their focus is on, is eating. It’s just born out of necessity. If they don’t have enough fat, they won’t survive hibernation. Brutal lesson to learn, if you’re a bear.

Heiko Jansen studies grizzly bears at the Washington State University's Bear Center.

Werner: Grizzly bears can easily double their body fat in the lead up to hibernation. Some of the brown behemoths here at Washington State University's Bear Center will reach more than 700 pounds!

Wild bears developed the ability to hibernate as a way to survive winter, when food is scarce. The fat they store up over the summer and fall fuels them through their six to seven month slumber.

And during that time, their bodies change in surprising and incredible ways.

Joy Erlenbach, WSU Bear Center Manager

Joy Erlenbach, WSU Bear Center Manager: They don’t eat or drink or urinate or defecate during the hibernating season. The bear’s metabolism decreases drastically. Their heart rate drops from somewhere around 60 beats per minute to much lower, maybe around 10 beats per minute.

Werner:  But perhaps the most remarkable adaptation during hibernation is that the bears become diabetic, or something that looks a lot like it. Their bodies become resisitant to insulin, a hormone that regulates blood sugar.

Jansen: What we see in bears looks very similar to what happens in diabetic humans. The big difference, though, the bears transition into and out of that state every year. So they exhibit a reversible, if you want to call it, diabetic state. Which is not something that’s very easy to do for humans.

Werner: Heiko Jansen studies seasonal changes in grizzlies, with help from the biotech giant Amgen, he is trying to solve the mystery of how the bears make this switch. The answer could one day lead to a treatment for human diabetes.

But to study this phenomenon you need access to hibernating bears, and the WSU bear center is the only place in the world where captive grizzlies hibernate.

The WSU Bear Center is the only place in the world where captive grizzly bears hibernate.

Jansen: We know so little about bear physiology that every time we generate a hypothesis, it’s almost invariably rejected because we just know so little. And despite our best efforts, the questions we ask are almost always answered in a very different way than we expected.

Werner: Many of these bears were nuisance animals rescued from the wild. And studying a wild 700-pound grizzly is no picnic.

Jansen: The bears are not something you can mess with. Even trained bears will rear their ugly heads at time, unpredictably. So we have to work with them in a protected environment and very, very carefully.

Erlenbach: The bear center has worked to train bears because, if we can work with trained bears, we can avoid the need to anesthetize them to do simple procedures like blood draws and echocardiograms.

Erlenbach: We feed the bears honey when we’re doing voluntary blood draws because they like it and it’s a way to reward them for working with us and it’s also a way to keep their mouth occupied. As soon as we start feeding them honey, we can ask them to sit, and we can ask them to lay down, and then we can ask them to stick out their foot and then they’ll stick their foot out through one of the slats in the crate and we’ll be able to do a voluntary blood draw that way.

By feeding the bears honey, scientists are able to get a voluntary blood sample.

Werner:  But not every bear is so accommodating. Some have to be tranquilized.

Erlenbach:  We’ll load up a darting pistol with the drug that we’ll use to anesthetize the animal, and we’ll use that to inject the drug into the animal, and then a few minutes later, the bear will basically fall asleep.

Werner:  Researchers can then draw blood and take tissue samples. The key to understanding how beras switch in and out of a diabetic state may lie in the bear's fat cells. Here in Jansen's lab they're growing grizzly fat cells, hoping to get an up-close look at the mechanism that allows grizzlies to go from being diabetic to non-diabetic, and back again.

Scientists study a tranquilized grizzly bear.

Jansen: Our hypothesis is that it’s occurring at the fat cell, so we wanted to work with those cells directly. Somewhere within that cellular molecular machinery is a mechanism that can explain this switch. I think ultimately the hope of everyone is that we would be able to treat diabetes. Of course we all realize that it’s a very long shot and we’re working with exotic species that have mechanisms that we don’t fully understand, but insulin seems to do similar things in the bear that it does to people, and thereby understanding those mechanisms could allow diabetics to overcome their disease.

Jansen: Studying the bears has forced us to rethink so many things not only about our biology but their biology. We’re understanding and learning more every day.

Werner: As long as food is involved, the bears at the center are happy to help.



Made possible in part by

Michael Werner

Michael Werner is a five-time Emmy Award-winning filmmaker and journalist. His work has been featured on The PBS NewsHour, HBO Films, Showtime, PBS QUEST, CBS This Morning, MSNBC, The Associated Press, PBS SciTech Now, Nat Geo Wild, PBS EarthFix, Voice of America TV, The World Channel, Gawker Media, The U.S. Olympic Committee, and the Cannes International Film Festival. In 2014 Michael won the American Association for the Advancement of Science Journalism Award for his story Wolves and the Ecology of Fear. He has won Emmy awards for producing, photography and editing and his work has taken him from the Arctic to the Equator.

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