THURSDAY, Nov. 12, 2009 (HealthDay News) -- Not a big fan of dieting? Join the club. But new research in rats hints at why weight loss is so tough -- perhaps as tough as kicking drug addiction.
In the study, rats weaned off a high-calorie diet showed the same effects on the brain as withdrawing from drugs and alcohol.
Rat brains aren't the same as human brains, of course, and human neurology may work differently. But study author Pietro Cottone said the research suggests there's indeed a link between yo-yo dieting and cycles of addiction and withdrawal.
Yo-yo dieting, "a common habit of many chronic dieters, generates dependence," explained Cottone, an assistant professor Boston University School of Medicine. And when people who typically overeat stop overeating, stress hormones in their brain jump into action, he said, potentially leading to "anxiety, decreased motivation and rejection of other food alternatives."
In other words, their diet fails.
Scientists are fascinated by overeating, in part because of its link to evolution. In the resource-poor world of long ago, humans evolved to understand the importance of finding and recognizing food and coping with its scarcity, Cottone pointed out. Now, however, food is available in many cases, and this "sudden abundance" is killing people through diabetes and heart disease, he said.
Researchers know that food activates circuits in the brain that give us a feeling of reward, he said. Sex and occasional drug use can do the same thing.
But what about the reverse -- the brain activity that makes people stressed when they withdraw from drugs? Could it work the same for food?
To find the answer, Cottone and colleagues gave rats a regular diet for five days and then switched them to a chocolate-flavored food that was high in sugar.
Not surprisingly, the rats didn't want to switch back to the ordinary chow after their glory days of dining on the equivalent of rat junk food. When deprived of the sugary food, they showed signs of anxiety, and their brains acted as if they were withdrawing from alcohol or drugs.
"A history of dieting and relapse generates anxiety. The next attempt to avoid junk foods is going to be more painful and stressful than the previous one, and therefore the likelihood of relapse is going to be progressively higher and higher," Cottone said.
But there was one bright spot: Researchers found they helped the rats do better by inhibiting a system in the brain that contributes to stress. It's not clear, though, if a treatment for human obesity could ever arise from this.
The findings were published online in this week's Proceedings of the National Academy of Sciences.
Cynthia Sass, a registered dietitian and author in New York City, said the study results fit into the wider picture of how people deal with food. "Often, people with compulsive eating blame themselves or feel that if they just had enough willpower they could stop," she said. "Understanding that this is a disorder similar in nature to drug addiction can help people see that they need formal treatment."
After all, she said, "the body is really one big chemistry lab, and the chemicals in our body react with chemicals from food or substances like alcohol or drugs. We are seeing that food may parallel the effects of drugs in terms of creating chemical reactions in the body that allow people to avoid negative emotions. The differences are that each drug may carry unique side effects."
Learn more about obesity from the U.S. Centers for Disease Control and Prevention.