The obesity problem in individual U.S. states appears much greater than official health surveys have indicated, according to a new study.

The problem, researchers found, is that the telephone surveys used to estimate states’ obesity rates are prone to error - namely, that female respondents underestimate their weight, on average, while men often add inches to their actual height.

National estimates of the obesity epidemic, however, are more on target, because the methodology used is different.

It’s estimated that one third of U.S. adults are obese, and that national statistic is probably a close reflection of reality, according to Dr. Majid Ezzati, an associate professor of international health at the Harvard School of Public Health in Boston.

But, Ezzati told Reuters Health, his team’s findings indicate that individual states’ obesity levels are “grossly underestimated.”

The disparity between national- and state-level obesity estimates stems from differences in how the data are collected by the Centers for Disease Control and Prevention. Nationwide data are gathered through the National Health and Nutrition Examination Survey (NHANES), where respondents are interviewed in person about their height and weight, and then asked to have a physical exam.

State statistics are collected via the Behavioral Risk Factor Surveillance System (BFRSS), which asks respondents to give their height and weight over the phone.

By comparing information from this survey with data from the NHANES project, Ezzati and his colleagues found that every U.S. state’s obesity burden was underestimated.

In 2000, Americans’ phone-survey responses indicated that nearly all U.S. states had an obesity rate below 24 percent, according to the report in the Journal of the Royal Society of Medicine. But when Ezzati and his colleagues “corrected” these data using NHANES numbers, they found that most states had obesity rates higher than 24 percent.

Texas and Mississippi had the highest obesity rates among men, at 31 percent and 30 percent, respectively. Four states - Alabama, Louisiana, Mississippi and Texas - tied with Washington, D.C., for the highest obesity rate among women, at 37 percent.

The study found that young and middle-aged women generally shaved pounds off of their weight when asked over the phone, while younger adult - particularly men - tended to overestimate their height.

All of this matters, Ezzati explained, because public health policies and programs aimed at fighting obesity are carried out at the state level. So it’s important to have an accurate picture of each state’s burden. The findings also highlight the fact that obesity is “very much a Southern problem,” Ezzati said.

To ensure that state data are more accurate - and that adequate resources go to the most needy states - Ezzati suggests that state survey numbers could be corrected in the same manner he and his colleagues used.

Better still, the researcher said, phone-survey respondents could be asked at the end of the interview to have an exam to verify their weight and height reports.

SOURCE: Journal of the Royal Society of Medicine, May 2006.