A colleague of mine at Uni was, I think, about 400-420 pounds, and she broke her femur thrice during Med School. It was embarrassing, to say the least, to go visit her and know that the reason why she broke a bone was her obesity, Then she decided to become a psychiatrist, and had to go to one too, to become a psychoanalyst,  and somehow she realised that all her fat was a way to keep people at a distance, to protect herself from harm (I am not sure I totally understand it. I mean, intellectually I do, but to me it is such a dysfunctional thing to do, I cannot feel it)**  She lost the weight, and now is a normal human being with a normal social life. I am sure she has weaker bones than most fats, but still, since she has achieved the size of a human, instead of the size of a small planet, her bones are just fine.