It's still a commonly held belief but a recent study concluded there may be no difference at all: http://www.slate.com/blogs/xx_factor/2014/02/27/breast_feedin

It's still a commonly held belief but a recent study concluded there may be no difference at all: http://www.slate.com/blogs/xx_factor/2014/02/27/breast_feeding_study_benefits_of_breast_over_bottle_have_been_exaggerated.html http://www.slate.com/blogs/xx_factor/2014/02/27/breast_feedi...