Dieting and fasting. Is there any room for treating yourself?

Im going strong on a 3day water fast. I don't plan on doing it for awhile I just wanted to get away from cravings of bad food like pizza and junk. I've already researched and planned to reshape my eating habits when im done such as fruits vegetables first week adding fish oatmeal etc....all the healthy low calorie foods. My main question is after say a week or 2 of eating well is there any room to treat yourself with something you used to eat like pizza or steak (not gorging yourself of course). Now i know its said that eating something like this could re-trigger those bad habits and send you back to eating all those bad foods. But if you had the will power to treat yourself once a weak for one meal; from a physical and weight loss standpoint would it really be that harmful to your diet?