You might get a bit jinxed as to what a career has got to do with belly whereas the general notion is the belly is the symbol of prosperity which shows a person who is content and happy with what he is doing. However, the trend seems to have changed now, thanks to new sciences like Kinesics and others.
Apparently, there seems to be a new culture or cult that has been developing among corporates and other high ranking jobs that a symbol of belly indicates the lethargy and the lazy attitude of a person and this would mean a no to the jobs. This parameter is being considered very seriously so if you are looking out for a job you know where you have to begin.
However, this does not mean that one has to turn up with a six pack ab, it only refers to a trim tummy that is not overbearing and something which shows that a person is fit and disciplined enough to take care of himself because if he cannot take care of himself then how can he take care of his work or his colleagues in the organizations.