BMI stands for "Body Mass Index". It is a way to account for your height as well as your weight. For example, a football player who is 6 feet 10 inches tall and weighs 250 pounds may be too small. An office worker who is 5 feet 4 inches and weighs 250 pounds is too big. The BMI is a way to "level the playing field".

Normal BMI is less than 25. The National Institute for Health (NIH) recommends surgery for people whose BMI is between 35 and 40 may if they have developed an illness from their weight. Examples would be high blood pressure, diabetes, and reflux although there are many others. For people whose BMI is greater than 40, the risk of developing weight related illnesses is so high that the NIH has recommended weight reduction surgery. People whose BMI is greater than 40 have a one in seven chance of living a normal life span. The higher the BMI, the worse it gets.