Immigrants who live in the U.S. long enough may see a cultural shift in their bathroom scales, a study published Tuesday shows.

Using data from a national health survey of more than 32,000 U.S. residents, researchers found a trend of increasing body mass index (BMI) among foreign-born respondents who had lived in the U.S. for at least 10 years.

After that threshold year, BMI rose in concert with years of residence in the U.S., according to findings published in the December 15th issue of the Journal of American Medical Association.

The rate of obesity among immigrants who had lived in the U.S. for at least 15 years, at 19 percent, was nearly on par with the obesity rate of U.S.-born survey respondents, which was 22 percent.

“After 15 years or more, an immigrant is more likely to look like someone born in the U.S.,” said lead study author Dr. Mita Sanghavi Goel, a researcher at Northwestern University Feinberg School of Medicine in Chicago.

It’s no secret that the collective American waistline has been rapidly expanding for the past two decades, and the fact that U.S. immigrants gain weight is not surprising, Goel told Reuters Health.

“But I think the magnitude of the change, the rapidity of the change, is surprising,” she added.

According to Goel and her colleagues, the findings suggest that the modern American diet and lifestyle - readily available calorie-dense and nutritionally dubious foods, coupled with a lack of exercise and reliance on “labor-saving technologies” - are feeding the nation’s obesity problem.

However, Goel pointed out that BMI among foreign-born residents does not appear to take off until after a decade of living in the U.S. She said it will be important to figure out not only why they gain weight after that 10-year mark, but also why they don’t earlier on.

“Maybe we need to learn more from immigrant communities,” Goel noted.

It’s possible, she speculated, that when immigrants first arrive in the U.S., they’re likely to live in urban neighborhoods with others from their homelands and maintain a traditional diet and lifestyle. After some time, perhaps after moving to suburban areas, they may adopt more Americanized ways of eating, Goel said.

A finding from the study that makes the weight gain among immigrants particularly concerning, according to the researchers, is the fact that foreign-born respondents were less likely to have discussed diet and exercise with their doctors compared with U.S.-born adults.

In general, Goel said, doctors need to do a better job of counseling patients on diet and exercise. But these findings, she added, suggest that doctors with large numbers of foreign-born patients need to pay particular attention to bringing up nutrition and exercise during routine visits.

The study is based on a federal health survey of 32,374 adults conducted in 2000. Of the respondents, 14 percent were foreign-born U.S. residents. Among those who had been in the U.S. for less than a year, 8 percent were obese, compared with 19 percent among immigrants who had been in the U.S. for at least 15 years.

SOURCE: Journal of the American Medical Association, December 15, 2004.