What medical condition stops you from losing weight?

I don’t get it, fat people say "Oh, I have this medical condition, so don’t call me fat"
But, there are food that burn fat, & they can exercise. So, is there a medical condition that no matter what, you can’t burn fat? Because I don’t really believe in their excuses. Also, what’s this about being big boned ? You’re fat, don’t blame your bones.