Big babies

I have a question for you ladies, do you think the size of your baby had more to do with genetics or what you eat during your pregnancy? I had a c section with my last daughter and an going to try for a vbac but I'm worried cause they said if your baby is bigger it makes it hardder. My dad was a big baby, me and my husband were big babies and so was my daughter. I ate pretty healthy while I was pregnant with her but I did eat the fast food everyone and a while. I'm just curious what all of your thoughts are! Tia