"If you're breastfeeding, your baby digests her meals very quickly; making her wait, hungry, for the next one could infuriate her.
For these reasons I, and many other pediatricians, recommend a strategy called "demand feeding," in which a baby is fed whenever her little belly desires. Such "cue" feeding helps your baby build the trust, security, and bond that come from knowing her cries are quickly heeded."
By Dr. William Sears, M.D.
http://www.amazon.com/Baby-Book-Everything-Revised-Updated/dp/0316778001