Lean rats — but not fat rats — are sensitive to a brain signal that makes them restless, find Catherine M. Kotz, Ph.D, and colleagues at the University of Minnesota and the Minnesota Obesity Center.
"The results point to a biological basis for being a couch potato," Kotz said in a news release.
Kotz's research team bred two colonies of rats. They bred lean rats with lean rats until they got a strain of obesity-resistant rats. They also bred fat rats with fat rats until they got a strain of obesity-prone rats. Given the same amount of food, the obesity-resistant rats stay lean while the obesity-prone rats get fat.
Motion detectors attached to the animals showed that obesity-resistant rats moved around much more than the obesity-prone rats. This held true from an early age — even before the obesity-prone rats got fat.
This suggests that getting people to be just a little more active may be the key to weight loss.
Obesity In The Head?
The scientists discovered that the brains of the lean rats were very sensitive to a brain chemical called orexin. When orexin was injected into their brain, the lean rats got even more fidgety than they were before.
But orexin injections didn't have much of an effect on the fat rats. Their brains weren't very sensitive to orexin.
Human brains, too, respond to orexin. It may be that an orexin-like drug could make people more active and thus help them lose weight.
On the other hand, why wait for a drug that makes you fidget?
"Many people focus on diet [to control their weight], but it may be more feasible for some people to stand or move more throughout the day," Kotz suggests.
The study appears in the online edition of the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology.
SOURCES: Teske, J.A. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2006; early online edition. News release, American Physiological Society.
By Daniel J. DeNoon
Reviewed by Louise Chang, M.D.
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