The world is made up of all sorts and sizes of folks!
This is a question that has been kicked around a number of times on scuba diving forums, with no concrete answers.
It is fair to say that we all should do our best to maintain as good a general health picture as possible, and it go without saying that scuba diving and fitness health should go hand in hand,,,,and smoking and diving really have no place in the same sentence. (IMO)
I persl. try to maintain my health for this at times challenging sport, as I do take it to the extremes on occasion.
If one is over weight and out of condition they should modify their diving and seek to improve their general fitness level.