No you can use soy as long as your baby does not have an allergy to it as far as I know. The things that I have heard about soy is that it is not all that much easier to digest bc human babies are made to digest animal protein like cow milk ad not plant protein like soy. The other thing is possible estrogen exposure in baby boys. there is a natural hormone similar to estrogen in soy milk. Don't know if you should worry though.
I switched my baby from similac advanced (with lactose) to similac sensitive (lactose free) because she was having a lot of poopy stools that looked funny and now she seems to tolerate this formula much better and she has less poopy diapers and normal looking stools
Hope this helps
SD
