C.G.
Just wondering why you are concerned? Remember that ultrasounds generally are not accurate at estimations of baby's weight if that is your concern. Providers using their hands to guess at size can be more accurate but it depends on the person.
As for "empty calories" like soda, candy, etc they will usually grow a bigger baby because of all the sugar. Women who gain more weight in pregnancy tend to have bigger babies but there are more health risks with gaining too much weight.
There is something called the Brewer Diet (try googling it) that recommends very high protein intake. Although there is limited data to support the protein intake for health reasons, many providers believe the high protein intake is reponsible for growing big babies.
Average baby weight at term is 7 pounds 8 oz with the range of normal being from 5 pounds 9 ounces to 8 pounds 13 ounces. Anything above and below that is considered outside the norm.
I believe that women just tend to grow certain size babies. If you are small and the baby's father is samll then of course you should expect a small baby and vice versa for big people. Good luck with the pregnancy.