Might be related to progesterone? That or estrogen. Both of those are produced in big quantities when early pregnant and women love eating then too! Of course right before your period is when progesterone drops- that is, a day or so before. Any more than that, and it is raised (two weeks or so before). Estrogen is made in bigger quantities closer to ovulation.
I was told by a medical friend of mine that your metabolism definitely increases prior to your period. I know that I completely pig out before my period. Now I don't stress about it that much with the increased metabolism info. Boy, I really hope that is actually the case.