The metabolic process produces free radicals at many different stages, and the body needs antioxidants, differnent ones for different free radicals, to neutralise them and avoid destructive effects on cells and tissue.
If you're missing the right antioxidants from your diet to deal with certain free radicals, the body and get them out of circulation by stuffing them away in calcium deposits in joints and adhesions in connective tissues (and possibly, don't actually know about this one, in fats too.)
The use of the word "toxins" in this sort of context is something of a red flag for me. It generally has the same level of scientific backup as talking about chakras, or Mercury rising in your adjacent house affecting your love life.
Do some reading then! Biochemistry (that's a type of science) awaits!
Edit: I agree in part though. "Detoxing" - just drinking lemon juice for 4 days is not going to do very much to help you along. Eating plenty of fresh fruit and veg, avoiding processed food, fags, booze and chemicals, and getting out of the city for a while, will.