See, that's why I love our *new* ped....at ds's initial (and only so far) checkup w/ him, he asked us "Is he on whole milk or breastfeeding" ... DS was 20 mos. And since he phrased it that way, I felt completely comfortable elaborating a little....and answered that "he's still nursing, he doesn't like cow's milk" which was just fine, from both points of view.
Parent's shouldn't have to hide things from their children's dr's. It just makes it that much harder to get good care, if the doctor doesn't know something, or thinks the exact opposite of what is true, because of intentional miscommunication...bad enough when they happen accidentally. (and I want to make it clear - I'm in no way saying anything against mothers who do have to do this. Just that it shouldn't have to be that way, and I'm glad that I don't feel the need to do so.)