Here's some truth for you.
We have to generate messages detailing injuries which cause work time loss. There are hundreds of injury messages because of injuries suffered during exercise or sports. I've never seen one claiming that the injuries (up to and including loss of limbs and loss of life) were in any way caused by the person being overweight.
I've never known any sickness to affect fat people and leave the skinnies alone or affect the fats more than the skinnies.
Although I do believe in discrimination when it comes to jobs that require a vast amount of physical exertion (police, fire fighters, etc.) I find that most of it is just plain based on stereotypes about fat people being lazy, uncaring about their hygeine, etc.
I have had two cases of people being lazy and uncaring about their hygeine. Both were skinny people, well within recommended weight limits.