Nearly two-thirds of the United States population is overweight. There are many ways to determine if a person is overweight, but experts believe that a person's body mass index (BMI) is the best way to assess an adult's weight in relation to their height.
A person with a high BMI may have a normal amount of body fat if they have a lot of muscle tissue. However, the risk of death and disease is increased for adults who are overweight and obese.
Reference: http://health.nytimes.com/health/guides/symptoms/obesity/overview.html?inline=nyt-classifier