A Los Angeles Times health column advises people not to believe that “our bodies [are] awash in ‘toxins,’… and that we should therefore go to dramatic lengths, such as ‘colon cleansing’ and chelation, to get rid of all this bad stuff.” 
My Take?
Experts quoted in the story explain, “Colon cleansing proponents say that the process gets rid of ‘metabolic toxins,’ parasites, and ‘environmental toxins.’ And, “there is absolutely no science whatsoever to back these outlandish claims.”
In fact, “some colon cleansing products may even be dangerous, because most colonic techniques draw fluid from surrounding tissues into the colon, which can lead to problems such as dehydration and low blood pressure.”
As I discuss in my book, Alternative Medicine: The Christian Handbook, in the chapter on colonics:
Unfortunately, there are no well-performed, controlled medical studies to support or refute this type of therapy. 
Further, the FDA classifies colonic irrigation systems as Class III devices which can only be marketed for medically indicated colon cleansing (such as before certain radiologic examinations). 
No system has been approved for “routine” colon cleansing to promote general well being. 
Some doctors believe that patients who feel better after colonics are responding to a placebo effect induced by their belief that colonics are helpful.
Reports show that colonic irrigation has been associated with at least one outbreak of amoebiasis (an infection caused by a tiny one-celled organism called an “amoeba” that can be spread by the use of improperly cleaned colonic equipment contaminated with fecal material). 
Other types of colon infections have been caused by colonics. Three cases of colonic tubes puncturing patients’ colons were recently reported, requiring emergency treatment to prevent systemic infections—those that spread throughout a patient’s body. Two deaths associated with coffee enemas have also been reported. 
Some doctors worry that colonics might change the normal bacteria in the colon, but this has never been reported. Other unproven concerns include the loss of intestinal muscle tone and normal defecation reflex, water intoxication, and electrolyte disturbances. People with any intestinal problem or illness should consult a physician before undergoing colonics.
We could find no studies to prove or disprove that colonics enhance health. 
No medical evidence supports the use of colonics other than for constipation and pre- or postoperative reasons. 
Adverse effects appear to be relatively infrequent. Yet when there is no evidence that something is effective, any risk is too large to take. 
We are also concerned that those who promote colonics do not place enough importance on having evidence to support their recommendations. 
There is no scientific basis for using or recommending colonics for general health.