I get why doctors go straight to, "It's the fat." It's not fair, but it's understandable.
Put yourself in the doctor's shoes. The majority of people they see are fat. Don't believe it? Look around the waiting room. First time I realized this was a revelation. My old doctor serves almost exclusively senior citizens, who got to be seniors by not being fat. Now I go to other, closer offices and I'm often the only person in the room who isn't overweight. And there's always some morbidly obese person with a cast on their leg. Wonder how that happened?
Imagine how many cases they get in a week that are due to obesity, or aggravated by it. It's kinda like doing tech support where you think you already know what the problem is because you see it every damned day. "sigh... another one". If you're sincerely listening, you'll often catch yourself out! But docs now days gotta run us through the office like herding cattle.