One can of diet soda contains about 46 mg, so you would have to drink 11 cans a day before the levels are considered ‘high’. Since sodas have no nutritive value, it’s a good idea to drink them in moderation, but there is no reason to avoid them completely just because you are breastfeeding. I know that while pregnant diet soda is a no no, according to my Doc, due to the aspartame in it & not knowing the effects it can have on babies. But my question is, if you cant drink diet drinks while pregnant, can you drink them while breast feeding? There are NO foods that a mother should avoid simply because she is breastfeeding. It is generally recommended that you eat whatever you like, whenever you like, in the amounts that you like and continue to do this unless you notice an obvious reaction in your baby to a particular food.