Am asking this for a friend. She is having lots of trouble BF, bleeding, blocked ducts, pain making her cry through every feed etc. and is giving the odd bottle of expressed BM for some relief. She cannot express much though and so is going to switch the BM for formula. What she wants to know is, if formula ruins the natural balance of a baby's gut, is it worth continuing to BF if she is giving say one bottle a day of formula, or will the damage be done and she might as well switch to FF and stop all the pain? Please no advice on continuing to BF, she has made up her mind to give one bottle of formula a day, so any knowledge about continued benefits of BF when also using formula?