Some people have no problem with being overweight. I used to be, but now some 85 pounds lighter and still losing, I'm almost as fit and trim as I was in high school. It's a constant struggle for me, so I have some empathy for those who may not be able to control their weight.
A man weighing 500 pounds and his wife wanted to adopt his cousin's child, but was prevented from doing so because, among other things, according to the social worker, he apparently can't take care of himself, let alone a child.
No matter how hard he tries though, obesity isn't a protected Constitutional class. Age, sex, race, religion and a few others are. But not being overweight.
The only cure is to eat less and exercise more.
Filing a lawsuit won't do it.