Many of the nutritional/diet gurus out there allow for a cheat day in their weekly meal plans. My boyfriend notably was a big believer in the Abs Diet series before we made the decision to try going primal. The author of the Abs Diet (his name escapes me at the moment) calls for allowing yourself entire cheat days, while others opt for the lesser cheat meal.
In my experience, there is evidence that cheat days can be both helpful and harmful. Cheat days can alleviate the fatigue and cravings from a dramatic change in diet for someone who is just starting out, as well as being a nice compromise when holidays or festive celebrations come around. On the other hand, cheat days or cheat meals can open the door for falling off the horse. This is especially likely for those of us who have a tendency for black and white thinking (I already screwed up lunch, the day's wasted, let's splurge on dinner!; I already screwed up the last two days, might as well start again next Monday).
So what are your opinions? Are cheat days helpful or harmful? What about in the beginning of a change in diet versus someone who has largely acclimated and has been staying on track? Are there any of you who do not need or crave cheat days? Does anyone experience any noticeable difference in their energy or other bodily attributes after a cheat day?