Here's an interesting article from the Smithsonian's Food and Think blog on food and cravings... something I've always wondered about. Sadly, there still isn't much information that we have on the phenomena.
--a wacky story:
f much about cravings is still a mystery, one thing has been clear in Pelchat’s research: a monotonous diet is likely to trigger them. In studies in which participants were fed only an Ensure-like liquid that provided all their nutritional and caloric needs for three weeks (and were required to finish it so they were full), she says, it took only two days for young adults to report huge increases in cravings. They all craved non-sweet foods. “We don’t know if it’s boredom, or the idea of restriction,” she says, “but clearly it isn’t nutritional need.”