Body Mass Index Healthcare professionals around the world often use Body Mass Index (BMI) when determining whether patients are underweight, healthy weight, overweight or clinically obese. People who are clinically obese have a greater risk of developing diabetes, stroke, some cancer, and cardiovascular diseases. BMI has its drawbacks however. It does not take into account the patient's body fat content versus lean tissue (muscle) content. A 6 feet 2 inch athlete may have a higher BMI than a couch potato of the same height - but the couch potato may be overweight while the athlete is definitely not.