It had been a steady passage from alternative to mainstream for colonic irrigation – but that could change after researchers have rubbished the treatment’s benefits, and cautioned about its side effects – including cramps, nausea, vomiting and renal failure.

The process, rebranded from the agricultural sounding colonic irrigation to less intrusive “colonic hydrotherapy”, has become less taboo over the last two decades, having become popular with celebrities desperate to lose weight.

Princess Diana was said to be a fan, and the procedure - infamously trialled on television by the comedian Richard Blackwood and others for a celebrity health programme – is offered among detox treatments at most spas.

During a normal 45-minute session, which currently costs between £60-£90, about 60 litres of filtered water is used to flush the colon, after which users supposedly benefit from increased wellbeing, better skin, smoother bowel movements, and feeling lighter.

But a new, comprehensive review of research has chronicled the side effects suffered by some users of “the internal bath”, from cramping to renal failure – when the kidneys fail to adequately filter toxins and waste products from the blood.

Medics at Georgetown University School of Medicine, who examined 20 studies published in medical literature during the last decade, expressed concerns over the treatment’s regulation.

They concluded, in a paper published in the Journal of Family Practice, that while there was little evidence of the much-vaunted benefits from the treatment, there were “an abundance of studies noting side effects of using cleansing products including cramp, bloating, nausea, vomiting, electrolyte imbalance and renal failure”.

The same was true of other less

intrusive colon treatments which can be widely purchased on the internet, they said.

The paper’s lead author Ranit Mishori, a specialist in family medicine at Georgetown, said: “There can be serious consequences for those who engage in colon cleansing whether they have the procedure done at a spa or perform it at home.

“Colon cleansing products in the form of laxatives, teas, powders and capsules... tout benefits that don’t exist.”

She added that some treatments had also been associated with aplastic anaemia (where bone marrow does not produce sufficient new cells to replenish blood cells) and liver toxicity.

The doctors also expressed concerns colon cleansing services were being offered at some spas and clinics by operators claiming they are “colon hygenists” but who had little or no medical training.

In the UK, the lead body for colonic treatment is the Association of Registered Colon Hydrotherapists (ARCH), which maintains a register of therapists who have qualified at a recognised training course.

NHS advice states colonic irrigation is still a complementary therapy, and “there is currently no medical or scientific evidence to prove its effectiveness”. However, it says, the procedure is usually safe.

As colonic treatments are mostly undertaken in private, statistics on the number of users are hard to establish.

Anecdotally, doctors have said patients admitted to hospital following colonic irrigation have been diagnosed with a perforated colon – obtained during the procedure caused the tip that injects the water or from overpressure causing failure of a weak spot in the colon wall.

Scottish surgeon Sir William Arbuthnot-Lane, who worked at Guy’s hospital in London, is credited with pioneering treatment for constipation in the early 1900s.

His work led him to advocate eating fruit, vegetables and bran cereals as a way to control bowel problems. His views were dismissed by doctors and medial authorities at the time, leading him to ask to have his name removed from the medical register in order to promote the New Health Society, the first organised body to deal with social medicine, in 1925 to publicise his views on healthy diet and life.

Dr Mishori added there were other ways to increase well-being. She said: “Eat a balanced diet, exercise regularly, get six to eight hours sleep and see a doctor.”

Celebrity fans of the treatment

* Courtney Love, the wild woman of rock, had regular colonic treatments to help her detoxify and lose weight. "I would fast several times a year and go for regular colonics," she said. "They really did the trick for me." She stopped in 2007 following a fraught car journey home to use the lavatory after one treatment went "horribly wrong".

* The actor Ben Affleck said he would never repeat colonic irrigation after a traumatic experience in 2007. "I lost my virginity all over again that day in so many ways," he recalled. "I don't think I will be having it done again." He had been trying to adopt a healthier lifestyle after the birth of his first daughter.

* Princess Diana is credited with starting the fad in the 1990s. She had weekly treatments which she said "take all of the aggro out of me".