Most of them are definitely beneficial in that they get rid of some of the rubbish resulting from junk food and over indulgence, however heavy metals such as mercury have a half-life of fifteen to twenty years in the human system so there is not much hope that one of the miracle plans will get rid of all of it overnite. All is not lost, however as one can adjust one's diet and begin to notice benefits almost immediately. One needs both short term and a long term strategies. Fasting is also an extremely effective measure. Some people recommend Chelation Therapy, which is a treatment where specially shaped molecules bind to the toxic metal and it is then removed from the body by the kidneys.
Prevention is always better than cure so avoid junk food and drink pure water.
Note that Chelation therapy and eating sulfer-rich foods reduce trace elements so taking a mineral supplement after the treatment is a good idea. Lead In the ancient world and the middle ages, sugar of lead or lead acetate was used to sweeten wines usually resulting in severe and widespread lead poisoning. Something similar happened in England in the 18th Century when the cider producers used it for the same purpose. The resulting symptoms were so common that they became known as Devonshire Colic. Its use in sweetening beers was banned in England in the early part of this century.