In 1991, the National Institutes of Health examined this issue extensively. Their findings are what we use to identify patients that are most likely to benefit from bariatric (obesity related) surgery: to be a candidate for such surgery, a person must have a BMI over 40 (or a BMI over 35 with serious co-morbidities). There are other factors we consider when attempting to identify the best candidates for surgery, but these are the most basic criteria. Other factors we consider are willingness to adhere to a lifelong modification in daily diet and exercise, psychological stability, and if an effective social support system exists. Candidates for surgical treatment must also have previously attempted to lose weight by dietary and lifestyle modifications.
What is the significance of the BMI?
Currently, the body mass index (or BMI) is considered the best available indicator of excess body weight. Someone who is 20 percent or more over their ideal body weight typically has a BMI of 30 kg/m2 or higher. Clinically severe (or morbid) obesity is considered to be 100 pounds or more over ideal body weight, corresponding to a BMI of 40 kg/m2.
People with a BMI greater than 35 kg/m2 and serious health problems related to obesity are also categorized as having clinically severe obesity. BMI is used to predict which patients are at the highest risk for weight-related medical problems and identify which patients would benefit most from procedures designed to help them lose weight. People with clinically severe obesity are at a much greater risk of serious health problems and death than those of the same age at ideal body weight.
Here are some examples of medical challenges potentially facing those with high BMIs (over 35-40 kg/m2):
Other problems related to obesity can include depression, low self-esteem, physical disability, social discrimination, and unemployment -- to name only a few.