I'm curious why some people are so anal about free days. It seems like one of those old myths that just won't die. You know like eating fat makes you fat, you can spot reduce your belly by doing situps, bodybuilders don't do steroids, etc... There are some people that seem to still believe there is some unexplainable magic behind dieting. They seem to think that even if they bust ass all week with their diet and follow it to a tee, that one bad meal on the weekend will utterly sabotage their progress and make them fall behind. Sad part is that it can't be farther from the truth.
At worse having a bad day is 6 steps forward and 1 step back, which isn't that bad of a ratio in reality. But perhaps it's not even a full step back. We all know that dieting inevitably slows down metabolism no matter what we do. And if we are strict straight through the diet with absolutely no free days it is bound to shutdown even faster. So by having a free day you may take a step back on that day, but you've boosted your metabolism and assured your body it isn't starving. Therefore your metabolism will kick back up a bit. It won't be back to full but nonetheless it will be better off than had you not done a free day.
Of course you can screw anything up so if you have 8000 calories on your free day then yes you can essentially take 6 steps back and get nowhere. But if the average dieter who is getting a 500 calorie deficit in food alone combined with the deficit created by cardio and weights then it's not hard to come to the conclusion that after 6 days you can be up to a 4000 calorie deficit. Now you take a free day on your 7th day and get about 500 calories above maintenance. And believe me that many calories will make you feel like an absolute pig after dieting all week. So by end of 1 week you're still at a 3500 calorie deficit, which is still a pound of fat. So Billy Joe who insists on eating perfect all the time is 500 calories lower than you. Big deal. Billy Joe's metabolism is also slowing down faster so in the coming weeks when you are still maintaining the same basic metabolic rate and losing weight at the same caloric level, Billy Joe is finding that he has to lower his calories more to continue to lose weight.
This is a bit oversimplified but hopefully people get the picture. There is nothing magical about dieting. Eating perfect all week then slipping up and eating some pizza and beer does not sabotage your diet. In fact it may help in the long run as it will curb cravings, boost your metabolism and make the next week of the diet easier to handle. So damnit people quit beating yourself up if you want a bad day so long as you keep it within reason. Say no more than 500 calories above maintenence. It's also a good idea to eat a high level of carbs on this day to replace glycogen stores which are no doubt getting low after a week of dieting. Do this and I guarantee that when you workout the next day you will get an awesome pump.
Perhaps in the final few weeks of a diet where you are approaching very low levels of bodyfat you may decide to ace the free day. Your metabolism has slowed down a lot either way at this point and you just want to finish off asap. Or maybe you want to do a fast diet cycle of only 4-5 weeks to lose a few pounds. With that short of a diet you probably should skip the free day as well because your metabolism won't get too bad in that short of time and if you can't handle dieting for that short of time without a break then you need to learn some self control. However those that are planning long diets such as 12 weeks or longer, you should plan for free days, at least during the first 2/3 of the diet as it will help you in more ways than it could hurt you.