does food effect life span?

[Maxy24]

I've been recommending my friend switch her dog's food but her argument is that her last dog was fed this food and lived to be 14 and had no major health problems. So I was wondering if food actually affected life span or not. I don't think it does but I'm not really baseing that on anything. People have also said that on the food they are feeding their dogs have soft coats, do you think they really do or just that you don't know a really soft coat until you've felt your dog on a high quality food and they just thought it was soft because they have never felt a genuinly soft coat?