Here's a little experiment: Go to a foreign country for a few years, then come back. Chances are, when you get off the airplane at home, you will reach the conclusion that Americans are fat people. And, according to a new study, just moving to America is enough to make a person fat.

What the researchers wanted to know: Are immigrants more likely to be obese the longer they've lived in the United States?

What they did: The researchers used data collected in 2000 from a national health survey that is conducted by the U.S. Bureau of the Census on behalf of the National Center for Health Statistics. As part of the study, people are asked where they were born, how long they have lived in the United States, and their height and weight, which is used to calculate body mass index (BMI). BMI is a measure of obesity; for this study, they defined obesity as having a BMI higher than 30.

What they found: People who were born in a foreign country were less likely than U.S.-born people to be overweight and obese. But the longer they'd lived in the United States, the more likely they were to be overweight or obese. Foreign-born people who'd been in the United States for at least 15 years were about as likely as U.S.-born people to be overweight or obese.

What the study means to you: The researchers weren't looking at why immigrants catch up with their U.S.-born counterparts, but they suggest several possible reasons, including that immigrants might become more sedentary after they move here or pick up worse dietary habits.

Caveats: The participants reported their own height and weight; it's conceivable that immigrants might consistently underestimate their own weight. Also, the survey is given only in Spanish and English, so other immigrants might have been left out if no translator was available.

Find out more: For related U.S. News coverage and other information about obesity

Figure out your BMI

Read the article: Goel, M.S., et al. "Obesity Among U.S. Immigrant Subgroups by Duration of Residence." Journal of the American Medical Association. Dec. 15, 2004, Vol. 292, No. 23, pp. 2860-2867.

Abstract online: http://jama.ama-assn.org