From Correspondent Andrew Holtz
PHILADELPHIA, Pennsylvania (CNN) -- The discovery of a gene that controls obesity in certain mice created anticipation of powerful new treatments for overweight people. But the latest research indicates that the link between appetite and weight is more complicated in human beings.
Studies showed that the mice were obese because of a broken gene which prevented their bodies from producing a substance that warned their brains that they were gaining weight. But when scientists injected a substance called leptin, the mice seemed to hear the alarm bells, and began to lose weight.
When geneticists at Thomas Jefferson University tried to apply that research in humans, they couldn't even find the so-called OB genes in overweight people.
What's more, leptin production in most obese people studied seemed to work at the same levels as in lean people.
Dr. Jose Caro of Thomas Jefferson University says that although a majority of obese patients have plenty of circulating leptin, their brains don't seem to be responding to a crucial message: Stop eating.
Researchers believe that eating more food produces more body fat, which boosts production of leptin. The leptin tells the brain to lose its appetite, so people eat less food and body fat drops.
In obese people, the system works well initially. Body fat levels rise, and so do leptin levels. But then there is a breakdown, and their brains don't seem to get -- or act on -- the signal that their stomachs are full and that they need to eat less.
"So what we are trying to do now, and what many labs are trying to do, is figure out why the brain is blind," Caro says.
But that means simply giving overweight people extra leptin may not make a difference.
What the leptin research has highlighted is that obesity is more complicated than was previously believed. So, researchers say, obesity is not merely a failure of will power.
"Every obese patient should be treated with the same respect, with the same attention that anybody with diabetes or anyone with hypertension," Caro says.
In a nation where as much as 33 percent of the population is overweight, obesity still carries a stigma. Nancy Harnish, who lost 60 pounds by dieting when she took part in the leptin study, says she feels relieved that obesity may have some genetic roots.
"You can try as hard as you can, but you know there's still something internal that's going to trigger this," she says. "It gives you a sense of relief. It alleviates some of the guilt associated with why you are overweight."
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