An op-ed piece in The New York Times introduces a fascinating concept that grizzly bears might have to teach humans. Not that they know it themselves, but it appears that over the millennia, grizzlies have evolved some genetic adaptations as amazing as a comic-book superhero’s ability to shape-shift and acquire uncanny powers. They can turn obesity into “a benign state in which weight gain has much-reduced health threats.”
The expert who suggests this is Kevin Corbit, a biotech scientist who works for Amgen. He knows these things because he has been collaborating since 2011 with Charles T. Robbins of Washington State University, who has been observing ursine metabolism for nearly three decades.
In late summer, Corbit says, a grizzly eats enough to gain as much as 16 pounds a day and achieve a condition of benign obesity. Then, for those who skipped school that day, the bear spends about half the year in a state of suspended animation known as hibernation. During this time it doesn’t eat, drink or carry out any eliminatory functions. All it does is maintain life by slowly burning stored fat.
A pathologically obese human stores fat in the liver and muscle, while a bear’s body finds nooks and crannies to stash the fat cells where it does no damage. Somehow these big furry organisms are able to be fat without tissue inflammation, and to tolerate permanently high cholesterol. But the really astonishing thing is, bears don’t develop diabetes. Corbit explains:
The type of diabetes associated with human obesity is a result of the body’s inability to respond to the hormone insulin and so is referred to as ‘insulin resistance.’… Bears are able to modulate their insulin responsiveness, so that when they are most obese, in the fall, they are most insulin sensitive…. [T]heir cells retain the capacity to take instructions from insulin. The bears render themselves completely insulin resistant while in hibernation; they become, in essence, diabetic…. Put another way, bears naturally and reversibly succumb to diabetes.
Because of mutations that occurred in key genes, the changes that go on in the systems of grizzly bears let them come out of hibernation good as new:
Hibernating bears differ from diabetic humans in that they maintain normal blood sugar levels while in this insulin-resistant state. Once they wake, in the spring, the grizzlies restore their insulin responsiveness. So bears modulate insulin sensitivity not to maintain normal blood sugar levels, but to control when fat is stored and when it is broken down. Bears also shut down their renal function during hibernation, resulting in badly scarred kidneys and high levels of blood toxins that would kill a human. What is truly remarkable is that the bears’ kidney failure is reversible: Upon awakening from hibernation, their kidney function is fully restored with no lasting damage.
Even more amazing, a small fraction of the human population also has a specific gene mutation that lets them stay sensitive to insulin even in the midst of obesity. Weird as it sounds, this idea of “healthy obesity” as experienced by bears could indicate the path to drastically reducing certain risks associated with human obesity.
Your responses and feedback are welcome!
Source: “A Grizzly Answer for Obesity,” NYTimes.com, 02/12/14
Image by Scott Calleja