Obesity

The Epidemic of Obesity

After a gradual but sustained increase, the prevalence of obesity in adults in the United States has reached a plateau, with about one third of adults currently meeting the body mass index (BMI) criteria for obesity, according to data from the November 2007 National Health and Nutrition Examination Surveys. The prevalence of obesity in U.S. children, although it has tripled over the past 30 years, has also shown signs of reaching a plateau. Unfortunately, the global prevalence of obesity is steadily increasing, multiplying threefold in the past 20 years. Ten percent of children worldwide are considered obese. An additional review of the epidemiology of obesity demonstrates an overall increased incidence in those affected by poverty.

What is Obesity?

The current definition of obesity, for adults and children, centers on a person's BMI, the ratio of one's weight (in kilograms [kg]) to the square of one's height (in meters [m]). The metric formula for BMI is as follows: BMI = kg/m2. Although it is not a direct measure of adiposity, BMI has been shown to correlate with body fat. In adults, a person is overweight when his or her BMI reaches the range of 25 to 29.9 kg/m2; he or she is obese when his or her BMI is ≥30 kg/m2. As natural fluctuations of the appropriate ratio of weight to height occur in growing children, the use of BMI for children greater than 2 years of age is based on the percentile of BMI for gender and age from the 2000 Centers for Disease Control growth charts. Obesity in children under the age of 2 is determined by simple weight-for-height values. BMI weight categories in children are defined as follows:

• Obesity: ≥95th percentile or BMI ≥30kg/m2 (whichever number is lower)
• Overweight: 85th to 94th percentile
• Healthy weight: 5th to 84th percentile
• Underweight: <5th percentile

The 85th and 95th percentiles were chosen to avoid the overdiagnosis of obesity in muscular teens and the underdiagnosis in lower-BMI teens with higher percentages of body fat. With the increasing prevalence of severely obese children, new recommendations are being proposed to add an additional percentile category of ≥99th percentile, as those children will have significantly increased risk of the associated medical complications of obesity.

The Etiologies of Obesity

At its simplest, weight gain relates to an alteration of the balance between energy intake and energy expenditure in favor of intake. Today, increased intake can take many forms, including increased consumption of sugary drinks, increased portion sizes for meals and snacks, and increased restaurant eating. Energy expenditure has also fallen due to decreased physical activity in schools, decreased routine daily physical activity (e.g., walking to school/work from home), and a greater prevalence of automatic gadgets (e.g., escalators, elevators).

...