Inadequacy of BMI as an Indicator for Bariatric Surgery

BMI doesn’t distinguish between body fat and muscle mass, which weighs more than fat. Many NFL players have been labeled “obese” because of their high BMI, when they actually have a low percentage of body fat.

Inadequacy of BMI as an Indicator for Bariatric Surgery 
JAMA. 2012;307(1):88-89
Edward H. Livingston, MD

In response to overnutrition, some patients preferentially accumulate peripheral rather than central fat, preventing development of the metabolic syndrome.
When the ability to accumulate subcutaneous fat is limited, overeating results in central obesity and ectopic fat deposition that causes insulin resistance, diabetes, and ultimately life-limiting cardiovascular disease.
Thus, fat distribution, not overall fatness, is a critical determinate of the health risks of obesity.