Most "toxins" are ejected from the body by breathing. Sweating and urinating too, but your lung is the organ most busy with ejecting unneeded substances of metabolic or invasive nature that don't stay behind, like heavy metals.
However, detox diets and other placebo effects can be an important contribution to the overall wellbeing, especially if negative stress is a factor. Another reason is releasing or tapping into normally restricted resources, by associating yourself with someting bigger than yourself.
Some "detox" diets also seem to function because of undiagnosed food intolerance or allergies. Many people who go into (grainless) raw food diets and who notice drastic improvements may actually be gluten intolerant. Of course, the same improvements would occur if they'd switch to a gluten free nonraw diet with grains that do not contain this protein; like rice, buckwheat, corn, amaranth, millet, quinoa - to name some off the top of my head.
BTW, I've been reading this thread with great interest, all of it, it's very interesting to observe the sometimes unrestricted enthusiasm of vegans socialized within the Anglosaxon cultural sphere for this, hm, concentrate, and the absence of comments or quiet skepticism of those outside it. Belonging to the latter, and being new to sports related food concentrates, I'm not sure I really understand the purpose of this (or any other) bar, apart from perhaps temporally satisfying an initial psychological vacuum of sorts, like a cigarette. Is it about efficiency? Convenience was already mentioned, but I'm not quite buying into that, there's too many religious parallels. We got an achiever authority figure, leader, who disperses "his" strength and energy in a neat little package, and we got believers on the other side willing to absorb this somewhat harmless but nevertheless arbitrary collection of nutrients.
I'm sorry if my seemingly obsessive desire to rationalize each and everthing bores you to death, you can safely ignore this post and I wouldn't mind at all if my questions remain unanswered.
don't only question the system, but collaborate to improve it