It depends on what you mean by detox. A lot of diets have a "phase 1" which is supposed to detox you, but by that they mean a break from refined carbs such as sugar, and highly processed foods. It's supposed to cut your cravings for the bad stuff, to make it easier to stick to the next phase. This usually lasts for 1 or 2 weeks. South Beach, Sonoma, and Fat Smash all have this sort of phase, and each is a little different.
If by detox you mean cleaning out your bowels, that's something that has become popular based on myth and misconceptions. The experts tell us that our bodies don't need to do that because we are naturally self cleansing, and we don't build up toxins. We have a lot of topics on this in our "Does it Work" forum if you'd like to take a look.
Hope that helps