Since obesity can often be part of the body's natural functions, how does it make sense to call it a disease? Some people are born to be overweight unless very restrictive and there are a lot of people who can be mostly unharmed by what is labeled on the BMI scale as being severely obese. Whenever a disease shows physical signs, it is usually much more severe than physical inconvenience and implied diet correlation and usually is deadly if left untreated for years. Fat people can live for just as long as normal people, but some are definitely fat from various diseases and addictions and carry a much shorter life span.