Definition
Do you weigh more than you should? If so, you're like the two-thirds of American adults who are overweight. About one in three American adults is considered to be obese.
Obesity, in simple terms, is having a high proportion of body fat. Fat is important for storing energy and insulating your body, among other functions. The human body can handle carrying some extra fat, but beyond a certain point, body fat can begin to interfere with your health. For this reason, obesity is more than a cosmetic concern. Obesity puts you at greater risk of developing high blood pressure, diabetes and many other serious health problems.
The good news is that even modest weight loss can improve or prevent complications associated with obesity. Weight loss is usually possible through dietary changes, increased physical activity and behavior modification. For people who don't respond to these lifestyle changes, other more involved obesity treatments are available to enhance weight loss. These include prescription medications and weight-loss surgery.
http://www.mayoclinic.com/health/obesity/DS00314