Developments in Brief : If Your Jeans Don’t Fit, You Might Be Able to Blame It on Your Genes

Hereditary factors play a much more important role in obesity than environmental ones, a major study of male twins has found.

About 80% of a person’s adult body weight can be accounted for by genetic factors, a relationship that remains constant even into middle age, said Dr. Albert Stunkard of the University of Pennsylvania.

Although his study involved only male twins, Stunkard said his earlier work indicates that the relationship between obesity and heredity in females is as strong, if not stronger, than it is in males.

The new study, reported in the current Journal of the American Medical Assn., involved more than 4,000 male twin pairs, half identical and half fraternal. The weight of identical twins remained closer than the fraternal twins, both at ages 20 and 45. Earlier studies suggested a relationship between heredity and obesity, but none have involved so many twins tracked over such a long period of time.

Despite the findings, Stunkard said he did not want his study to discourage people from trying to control their weight just because obesity runs in their families.

“We have an environment today in the United States that’s just made to order for obesity,” he said. “You can produce obesity in just about every laboratory animal just by feeding it a typical American diet.”