More evidence to support my hypothesis that gut flora plays games with us. All it takes is one bacteria secreting a chemical that makes us feel like crap if we don't eat the sugars or whatever it craves and secreting something else that makes us feel good when we do.
Maybe resisting that sick feeling and staying on course means the rogue organism will starve to death?
There are gut flora organisms which can't be cultured outside the gut, or even outside certain portions of the gut. We don't know what a lot of them do, but there are something like 2kg (~4lb) of them in each of us. Being quite small, each of us is vastly outnumbered on the scale that war against these beasts is basically genocide (How To Make A Vegan Explode -101).