Maria, unfortunately, that's something that doctors do much of the time - recommend something that does not have scientific evidence to back it up. A lot of guidelines are based on nothing but personal opinion (or even feelings!) of some doctors. I work precisely in this area (my employer is near you - on Mission St. :-D ), evidence-based medicine. A classic example of a rule based on nothing other than feelings of one doctor is "Once a C-section, always a C-section."