A little of what you fancy does you good, apparently
Ego depletion is the idea that self-control is a limited mental resource. If used up, it impairs the ability to control yourself. This is particularly relevant to people who use a lot of willpower by resisting urges to eat certain foods while dieting, and may explain why they "give in" after a period of mental stress or in the face of strong temptation - their will power is exhausted. Moderation > deprivation.
http://en.wikipedia.org/wiki/Ego_depletion#Dieting














