Long-term exposure to American culture may be hazardous to immigrants' health (search).

A new study found that obesity is relatively rare in the foreign-born until they have lived in the United States — the land of drive-thrus, remote controls and double cheeseburgers — for more than 10 years.

Only 8 percent of immigrants who had lived in the United States for less than a year were obese, but that jumped to 19 percent among those who had been here for at least 15 years. That compared with 22 percent of U.S.-born residents surveyed.

The study, published in Wednesday's Journal of the American Medical Association, shows the flip side of the American dream of finding a better life in the land of plenty.

"Part of the American dream and sort of life of leisure is that you also have some of the negative effects, and obesity is one of the major side effects of the success of technology and just having a life of leisure," said co-author Dr. Christina Wee of Harvard Medical School. "It's a double-edged sword."

Previous studies have shown that immigrants tend to have healthier habits, including less smoking and drug use, than U.S.-born residents, and longer life spans. Researchers suspect that is at least partly because those who choose to immigrate could be unusually healthy, since uprooting to another country requires strength and vitality. But the earlier studies did not look at how obesity rates among immigrants changed over time.

The link between obesity and numbers of years in the United States was found in white, Hispanic and Asian immigrant groups. It was not seen in foreign-born blacks, but their numbers in the study were too small to draw any conclusions, said lead author Dr. Mita Sanghavi Goel of Northwestern University in Chicago.

"Trends in obesity among immigrants (search) may reflect acculturation and adoption of the U.S. lifestyle, such as increased sedentary behavior and poor dietary patterns," they wrote. "They may also be a response to the physical environment of the United States, with increased availability of calorically dense foods and higher reliance on labor-saving technologies."

Goel said it makes sense that exposure to America's fast-food culture would eventually rub off, but she said she was surprised by the magnitude of the change.

The results are worrisome, particularly since immigrants often face a language barrier and other obstacles to good health care, the researchers said.

While people tend to get heavier as they age, the study found that the weight gain in immigrants was above what would be expected from aging, Goel said.

The study involved data on 32,374 participants in a 2000 national health survey, 14 percent of whom were immigrants. The study relied on what the participants reported about their weight.

The study sends "a sobering message," said Dr. Glenn Flores, director of a Medical College of Wisconsin center that treats minority and immigrant children.

Flores said immigrants might do well to cling to healthy traditions such as diets rich in fruits, vegetables and fiber. And native-born Americans might want to adopt some of those "foreign" habits, too, he said.

Obesity in the United States "just isn't going to go away unless we rethink what we're doing," Flores said.