The problem of overweight in the American population may be even greater than previously suspected. A new study in the Archives of Internal Medicine reveals that the number of clinically severely obese adults is growing faster than any other group, quadrupling between 1986 and 2000.
The numbers increased from one in 200 adults in 1986 to one in 50 adults in 2000 - growing twice as fast as the proportion of Americans who are simply obese, according to the study by California-based research organization the RAND Corporation.
To be classified as severely obese a person has to have a body mass index of 40 or higher - approximately 100 pounds or more overweight for an average adult man.
The body mass index allows researchers to define obesity and severe obesity over a population of people with varied heights and weights. The index is defined as weight in kilograms divided by the square of height in meters. The standard cut point for obesity is a body mass index of 30 or more.
According to RAND, the typical severely obese man weighs 300 pounds at a height of 5 feet 10 inches tall, while the typical severely obese woman weighs 250 pounds at a height of 5 feet 4 inches.
The study involved around 1.5 million respondents and was based on the Behavioral Risk Factor Surveillance Survey, the world's largest telephone survey, conducted by the Centers for Disease Control and Prevention which tracks health risks in the United States. Height and weight are based on self-reporting.
RAND economist Roland Sturm, author of the report, said the study highlights a part of the 'obesity epidemic' that has remained hidden because most studies have focused on changes in moderate obesity, defined as a body mass index of 30 or more. He added that the widely published data on obesity in the United States therefore underestimate the long-term social and cost consequences of obesity because morbidity and use of health services are much higher among severely obese individuals.
He also explained that the findings challenge a common belief held by physicians that people who are clinically obese are a fixed proportion of the population and are not affected by changes in eating and physical activity patterns in the general population.
In fact, the study suggests that clinically severe obesity, instead of being a rare pathological condition among genetically vulnerable individuals, is an integral part of the population's weight distribution. As the whole population becomes heavier, the extreme category - the severely obese - grows the fastest.
The largest growth rate was among individuals with a body mass index over 50, about 150 pounds or more overweight. Sturm comments that although still rare, this group grew from 1 in 2,000 Americans to 1 in 400 during the study period (1986 to 2000). The typical man in that group weighs 373 pounds and is 5 feet 10 inches tall.
"These findings have enormous implications for the nation's health care system because treatment rates for diabetes, hypertension, and other chronic problems are several times higher among severely obese individuals than among the moderately obese," concluded Sturm.
The study 'Increases in Clinically Severe Obesity in the United States, 1986-2000' was published in the 13 October issue of the Archives of Internal Medicine.