Chances are fatsy lied to the doctor about his diet as well. Any medical professional who's actually done the first term which includes biochem and nutrition will know for a fact that a 320lbs person isn't eating healthily, but they won't necessarily challenge the patient's assertion unless they see a point in doing so. So when someone comes in and is morbidly obese but claims to exercise regularly and eat healthily, they usually just let that person keep deluding themselves as they know neither nutritional nor exercise advice will be followed anyway.