Morbid obesity, also referred to as “clinically severe obesity” or “extreme obesity,” was defined as the criteria for bariatric surgery by the 1991 NIH Consensus Conference Statement on Gastrointestinal Surgery for Severe Obesity as a BMI ≥ 40 kg/m^2^ or a BMI ≥ 35 kg/m^2^ in the presence of high-risk comorbid conditions.
Obesity was further classified in the 1998 NIH Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults into Class I, Class II, and Class III.