I’ve gained 5 pounds since last summer. My body mass index (BMI) is still fine, but I need to stop gaining to keep it that way.
Grizzly bears put my weight gain to shame. In the late summer, they eat some 50,000 calories per day and gain more than 100 pounds. Then, when they hibernate, they fast and live on their body fat. While sleeping the winter away, they don’t pee or poop. They conserve their energy by having heart rates around 15 beats per minute. When they emerge from their dens in the spring, the bears are much slimmer. In short, their “before” and “after” pictures are quite different.
Here’s the simple version of how grizzlies manage their huge weight transition: They first succumb to diabetes and then reverse slipping into that state. We know when they do this – researchers are now investigating how they manage the trick.
Lynne Nelson and Charles Robbins of Washington State University work with grizzlies kept in the only research-based grizzly colony in the country. They study the bears as they go through their annual transformations.
One secret to how grizzlies manage to stay healthy while becoming obese is that they have a lot of “good” cholesterol. And their cholesterol levels don’t change much when they pack on the pounds. Studying how they do that could one day help with interventions in human medicine.
A number of things the bears do while they hibernate are fascinating. The animals have a four-chambered heart, just like we do. But when they sleep the winter away, only two of the chambers keep working while two are at rest.
Even with that reduced cardiac output, grizzlies can stand up and move around during hibernation. Humans would black out in a similar situation. Again, studying what bears can do may help spur advances in human medicine.
Naturally, doing cardiac research on grizzlies requires some special approaches.
“We start training the bears when they are cubs for exams we’ll want to do on them throughout their lives,” Nelson told me. “It’s easier to start on an animal that’s 4 pounds rather than one that’s 400 pounds.”
Nelson, Robbins and those who work with them use positive reinforcement and “clicker training,” much like that used with many dogs today. Food is used as the ultimate reward.
“Bears are faster learners than dogs,” Nelson said. “They are problem solvers.”
The goal is to have bears trained so that researchers can draw blood from them and administer exams like electrocardiograms and echocardiograms (an ultrasound test). To facilitate the research, the bears are taught to go into a crate.
“They sometimes fight to get to go into the crate first,” Nelson said.
As I struggle with my extra 5 pounds, I marvel at the weight transitions grizzlies naturally go through each year – and I wish the WSU researchers well as they study bear metabolism and cardiac function, topics that one day may find application in human health.
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