Obesity epidemic in US under-estimated by up to 50 percent: study

The prevalence of obesity in the US states has been under-estimated by as much as 50 percent, according to a study.

In 2002, 28.7 percent of adult American men and 34.5 percent of American women were clinically obese, compared to the conventional estimates for that year of 21.9 percent and 21.2 percent respectively, it says.

The research, published in Britain's Journal of the Royal Society of Medicine by Harvard School of Public Health specialists, blames the discrepancy on low-cost data-collection -- and human nature.

The main tool for measuring obesity in the United States is the Behavioral Risk Factor Surveillance System (BRFSS), which uses telephone interviews with a cross-section of the population to get its data.

But the researchers say that, in these phone interviews, women of all ages often under-report their weight, and young and middle-aged men often over-report their height.

As a result, the calculations for body mass index (BMI) -- the yardstick of fat -- are being skewed, and the true picture is that America is even chubbier than it thinks.

The Harvard team says a more accurate measure of the average American comes from the National Health and Nutrition Examination Survey (NHANES), a small but precise sampling technique in which a person is interviewed face-to-face and is then weighed and measured.

Using the NHANES to correct the distortions in the broader BRFSS surveys, they found that the incidence of obesity has been greatly under-estimated since 1988, the starting year for the comparison.

These corrected figures suggest that true obesity prevalence rose from 16 percent to 28.7 percent from 1988-2002 among men, and from 21.5 percent to 34.5 percent among women.

"These are the first unbiased estimates of trends in the obesity in the US states and the results are staggering," said lead researcher Majid Ezzati.

"The obesity figures shown here are in addition to the percentage of the population that would be deemed overweight, so the true extent of weight health-related problems would be much higher than our findings reflected."

Ezzati expressed particular concern for a swathe of southern US states, where more than a third of the adult population is obese.

In 2000, Mississippi (31 percent) and Texas (30 percent) had the highest prevalence of obesity in men.

That same year, Mississippi (37 percent), Texas (37 percent), Louisiana (37 percent), District of Columbia (37 percent), Alabama (37 percent) and South Carolina (36 percent) had the most incidence of obesity among women.

The states with the lowest obesity rates for men in 2000 were Colorado (18 percent), District of Columbia (21 percent) and Montana (21 percent), and, for women, Colorado (24 percent), Montana (16 percent) and Massachusetts (27 percent).

Obesity is a worsening problem in almost every industrialised country, led by the United States. Worldwide, it is blamed for 2.6 million premature deaths each year.

BMI is calculated as weight in kilogrammes divided by the square of the height in metres. Obesity was defined by the researchers as having a BMI equal to or more than 30, and an adult was defined as an individual aged 20 or more.