Body Mass Index (BMI) is a measure of weight in relation to height. Although BMI is generally considered an effective way to evaluate whether a person is overweight or obese, there are exceptions. Some muscular people may have a BMI that puts them in the overweight range. However, these people are not considered overweight because muscle tissue weighs more than fat tissue.
According to the National Heart, Lung, and Blood Institute (NHLBI), a BMI from 18.5 to 24.9 is considered normal while a BMI of more than 25 is considered overweight. A person is considered obese if the BMI is above 30, and morbidly obese if the BMI is above 40.
Bariatric surgery is most often appropriate for people with a BMI of 40 or more, or 35 or more and experiencing obesity-related health conditions, such as high blood pressure or diabetes, and who also might have serious health complications related to obesity.