The Heart & Diving

The Heart & Diving

Overweight and Obesity

The terms overweight and obesity refer to a body weight in relation to height that is greater than is considered healthy; both conditions often (but not necessarily) result in a higher proportion of body fat, known as adipose tissue, compared with lean muscle mass. Overweight is applied to those with a somewhat elevated weight, and obesity to those who are extremely overweight.


  • 69% of adult Americans (more than two-thirds) are either overweight or obese.

  • Adult obesity rates have more than doubled in just over 30 years, from 15% in 1976–1980 to 36% percent in 2009–2010.

  • 10 years ago, the obesity rate was significantly higher among women than men; currently, the rates are essentially the same — within a few decimal places of 36% for both men and women.

Body mass index (BMI) is a common way of expressing the ratio between weight and height. The following equations are used to calculate BMI:

BMI is an important measure for understanding population trends, but it does have some limitations, as follows:

  • It may overestimate the proportion of body fat in athletes and others with a muscular build.

  • It may underestimate the proportion of body fat in older persons and others who have lost muscle mass.

Accordingly, BMI is just one of many factors that should be considered in evaluating whether an individual is at a healthy weight — along with waist size, waist-to-hip ratio and a measurement known as "skin-fold thickness."