Fastest Increasing Group of Obese Americans Are People 100 or More Pounds Overweight

The proportion of Americans with clinically severe obesity increased from 1 in 200 adults in 1986 to 1 in 50 adults in 2000—growing twice as fast as the proportion of Americans who are simply obese, according to a RAND Corporation study published today.

To be classified as severely obese, a person has to have a body mass index (a ratio of weight to height) of 40 or higher—roughly 100 pounds or more overweight for an average adult man. 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 RAND Health 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. As a consequence, the widely published data on obesity in the United States underestimate the long-term social and cost consequences of obesity because morbidity and use of health services are much higher among severely obese individuals.

RAND economist Roland Sturm, author of the report, said 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.

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.

In fact, the largest growth rate was among individuals with a body mass index over 50, about 150 pounds or more overweight. 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.

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, corresponding to a person 5 feet 4 inches tall and weighing 174 pounds, or 5 feet 10 inches tall and weighing 209 pounds or more.

“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,” Sturm said.

“With these growth rates, accommodating severely obese patients in clinical practice will no longer be an unusual occurrence,” Sturm said. “Doctors, hospitals and other health providers must be prepared to treat these people on a regular basis. This may require a substantial investment in new equipment.”

The RAND study, published in the October 13 issue of the Archives of Internal Medicine, was based on the Behavioral Risk Factor Surveillance Survey. The world's largest telephone survey, it is conducted by the Centers for Disease Control and Prevention and tracks health risks in the United States. Height and weight is based on self-reporting. Approximately 1.5 million respondents were included in the analysis.

RAND Health is the nation's largest independent health policy research organization, with a broad research portfolio that focuses on health care quality, costs, and delivery, among other topics.