ABSTRACT
The prevalence of obesity has increased dramatically in recent years. Obesity, or excess body fat, is usually operationally defined in terms of body mass index (BMI), calculated by dividing an individual’s weight in kilograms (kg) by the square of height in meters (m). The World Health Organization (WHO) and the U.S. National Institutes of Health (NIH) define overweight as a BMI of 25 to 29.9 kg/m2 and obesity as a BMI of 30 kg/m2 or greater. By this definition, nearly two in three U.S. adults (64.5%) are overweight or obese (1). Although the percentage of adults classified as overweight but not obese has been stable since the 1960s, the prevalence of obesity doubled between 1980 and 2000, rising from 14.5% to 30.5%, and that of severe obesity (i.e., BMI 40 kg/m2) more than tripled, increasing from 1.3% to 4.7% during this period (1,2). The proportion of U.S. children and adolescents who are overweight is also increasing. In 2000, the prevalence of overweight among those aged 2 to 5 years, 6 to 11 years, and 12 to 19 years was 10.4%, 15.3%, and 15.5%, respectively, as compared with 7.2%, 11.3%, and 10.5% in 1994 (3). Similar trends are occurring in many developed and developing countries. Worldwide, an
estimated 135 million people were obese in 1995; that number is projected to jump to 300 million by 2025 (4).
