Study - Binge-eating not solely caused by lack of willpower

BOSTON -- Binge-eaters who say they can't help it may be right.

A study suggests a weak gene, not feeble willpower, may be the cause for some people. The research may point the way to a future pill to tame their appetites.

The joint Swiss-German-American study makes the strongest case yet that genetic mistakes can cause an eating disorder, researchers say. Traditionally, eating behavior has been viewed as complex and cultural in its causes.

"Willpower is not always important to reduce weight. Some people can by willpower. Some cannot, and I think these patients have a hard time," said Dr. Fritz Horber, the leader of the binge-eating study at the Hirslanden Clinic in Zurich, Switzerland.

Researchers have been trying to understand the reasons for an epidemic of obesity, which raises the risk for heart disease, diabetes and many other ailments. About 30 percent of American adults are obese, up from 14 percent 25 years ago, according to government data. The surge is widely blamed on abundant high-calorie foods and sedentary lifestyles.

Heredity as factor

However, some researchers have also begun to link several genes to obesity, implicating heredity as an important underlying factor. Increasingly, eating problems are thought to stem from a subtle interaction of lifestyle and multiple genes.

Probably the most common eating disorder, binge-eating strikes up to 4 million Americans, according to the National Institutes of Health. Binge-eaters, who are usually but not always overweight, frequently and compulsively stuff themselves -- often in secret -- and feel ashamed afterward.

In this study, which was published Thursday in The New England Journal of Medicine, the researchers focused on a gene linked to obesity in earlier studies. Known as the melanocortin 4 receptor gene, it makes a protein by that name that helps stimulate appetite in the brain's hunger-regulating hypothalamus. If a mutated gene makes too little protein, the body feels too much hunger.

The researchers considered 469 severely obese white adults -- a quarter of them binge-eaters. However, the disorder was more common among the 5 percent with the mutated gene. All of them were binge-eaters, compared to just 14 percent of those with no mutated gene.

In another study in the same journal issue, a British team reported finding mutations of the same gene in more than 5 percent of 500 severely obese children. The genetic link was so strong that the researchers could use results from chemical tests on their genetic DNA to predict how much the children would eat at a meal.

Horber said other eating disorders, including other types of bingeing, probably stem from a variety of genes and environmental factors. However, he said the still-unnamed binge-eating syndrome tied to this gene is especially important because it is perhaps the most stubbornly resistant to dieting and exercise.

Horber said the binge-eaters in his study felt a wave of relief from guilt when they learned of the genetic cause behind their compulsion. Dr. Stephen O'Rahilly, one of the British study's researchers at the University of Cambridge, said one family in that study was so ecstatic over evidence of a physical cause that they made themselves T-shirts saying, "We've got an MC4 mutation."

Eric Ravussin, a Louisiana State University researcher on obesity genetics, said, however, that without more biochemical proof, he remains "a little bit skeptical" that these mutations -- and not others located nearby on the same chromosome -- are the syndrome's precise cause.

But Dr. Joel Habener, a diabetes expert at Boston's Massachusetts General Hospital who co-wrote an accompanying editorial, said the Swiss-led study demonstrates either the "genetic cause or a very strong association."

And he agreed with the researchers, who said future drugs acting like the melanocortin 4 receptor protein may compensate for the genetic defect. Habener said such chemicals are apt to be small molecules that can be delivered as pills.

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On the Net

New England Journal of Medicine: http://nejm.org

American Obesity Association: http://www.obesity.org