June 25 (UPI) -- An unknown hormone produced by fat cells might be responsible for weight loss after quick and excessive gain, according to a study with mice.
Researchers at Columbia University studied "overfed" mice and determined that the hormone helped them return to their normal weight after an excessive amount of nutrients. Their findings were published this month in the journal Cell Metabolism.
"We're now looking for this signal and we hope that once it's found, it will induce weight loss in more typical obese individuals who have gained weight slowly over time," Dr. Anthony Ferrante, a professor of medicine at Columbia University Vagelos College of Physicians and Surgeons, said in a press release.
People struggle to keep excess weight off after shedding the pounds, but studies have also shown it also is hard to maintain a higher body weight after excessive eating. One previous study found, for example, that the Massa people of Cameroon consumed more than 6,000 calories a day to gain 40 or more pounds, but lost all the weight eventually without dieting or exercising.
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For the new study, researchers rapidly fattened mice using a tube-feeding system. In two weeks, the mice gained 50 percent of their body weight -- the same as a 150-pound person gaining 5 pounds a day for two weeks.
When researchers stopped the tube-feeding and let the mice eat regular food, their weight rapidly dropped and returned to its previous level within another two weeks.
"This shows us that mice, like people, will naturally return to their original body weight when weight is gained rapidly," Ferrante said. "And we can use these mice to help us understand the physiology behind this process."
Although the hormone leptin has been shown to defend body weight when pounds are shed, the researchers found it had no impact on weight loss after excessive gain.
"We believe there's another factor coming from fat in overfed mice that tells the brain to reduce how much you're eating," Ferrante said.
And he said this only happens when weight is gained quickly.
The researchers saw differences in fat tissue between mice that gained weight rapidly compared with those that added pounds more slowly.
"We think there's a natural limit to fat, and when the fat senses that things have gone overboard, it sends a signal to the brain," Ferrante said. "When fat is gained slowly over time, the fat can probably adapt."
