They are increasingly used to treat diseases linked to the wrong gut flora, but faecal transplants may have several odd side effects

Weight gain – a trifling worry? (Image: Claudine Doury/Agence VU/Camera Press)

AS MEDICAL procedures go, they’re certainly not something to discuss over dinner. Faecal transplants are soaring in popularity as a treatment for a range of diseases. But a transplant from an overweight donor seems to have caused obesity in one recipient, raising the possibility that the process could also pass on other, more dangerous conditions.

Our gut bacteria appear to play a vital role in our health, and certain strains have been linked to disorders from asthma and eczema to diabetes, cancer and Parkinson’s disease. Faecal transplants supposedly offer a way to repopulate the intestines of an unwell person with gut bacteria from a healthy person. At least 80 clinics in the US now offer the treatment, and one of the UK’s leading centres, the Taymount Clinic in Hitchin, is relocating to larger premises to meet demand.

The treatments are a lifeline for people with recurrent Clostridium difficile infections of the gut, which cause diarrhoea and fever, and can be fatal. These infections can recur after antibiotic treatment, but are cured 90 per cent of the time after a faecal transplant.


Colleen Kelly, a gastroenterologist at the Miriam Hospital in Providence, Rhode Island, has carried out around 200 faecal transplants for people with C. difficile infections. In 2010, she gave a transplant to a 32-year-old woman whose teenage daughter was the donor. The girl was borderline obese, says Kelly, but otherwise healthy. The transplant was a success and cleared up the woman’s C. difficile infection.

Around a year later the woman returned, complaining of massive weight gain. She had always been a normal weight, but had become obese despite diet and exercise regimes – even a medically supervised liquid protein diet. “She said she felt like there was a switch inside her body,” says Kelly. “No matter how much she ate or exercised, she couldn’t take the weight off. She’s still overweight now, and she’s very frustrated.”

It is the first recorded case of obesity apparently resulting from a faecal transplant (Open Forum Infectious Diseases, doi.org/zzr). Since it’s a one-off, Kelly says she can’t be sure of cause and effect. The antibiotics the woman also took could instead be to blame, says Martin Blaser, a microbiologist at New York University, who has found that these drugs can trigger obesity by wiping out “good bacteria”.

But researchers have already seen similar results in mice: lean mice may gain weight after receiving gut bacteria from obese ones. Separately, a team in the Netherlands tried giving faecal transplants from lean donors to obese people with metabolic syndrome – in which insulin is less able to lower their blood sugar levels – to see if they would lose weight. The recipients remained obese, but became more sensitive to insulin and better able to deal with sugar in their diet.

There is a possibility that other diseases linked to gut bacteria, such as immune disorders and cancer, could be transferred, says Kelly. “We don’t know enough about the long-term risks.”

“People have been wondering if something bad was going to happen,” says Trevor Lawley at the Wellcome Trust Sanger Institute in Hinxton, UK. “It could potentially result in something more dangerous than obesity.”

Spin-offs

Emma Allen-Vercoe, a microbiologist at the University of Guelph in Canada, says she wasn’t surprised by the reported case of obesity. She knows of other doctors who have observed unexpected spin-offs after faecal transplants, but haven’t reported individual cases in the past. “My colleagues have certainly seen some interesting things along the way,” she says. “They will perform a faecal transplant for C. difficile and then notice that, hey, the person’s ulcerative colitis has cleared up, or, hey, they are not depressed any more.”

“My colleagues will perform a faecal transplant and then notice that the person isn’t depressed any more”

Kelly has her own stories. “I had one patient who had alopecia, and he had no hair on his body since he was 6 years old,” she says. “After his faecal transplant, he actually started to grow hair again, and he managed to shave.”

There are 68 registered clinical trials under way in the US, investigating transplants’ potential for treating diabetes, Crohn’s and HIV infection. But at the moment, there are no reliable records of how many people have had faecal transplants, and how many have experienced side effects. To move from anecdotal reports to firm evidence, Kelly is planning to launch a US national registry of faecal transplant procedures, tracking people for five years following treatment.

Kelly has now changed the way she screens people who offer to donate their faeces. “I have become very strict with my donors,” she says, not using anyone who might even theoretically pose a disease risk. That includes people with “Parkinson’s or multiple sclerosis or chronic fatigue syndrome, or anything that we just aren’t sure about”. She also discusses the risks at length with potential recipients.

It is unlikely that everyone receiving a faecal transplant gets to hear the same warnings, however, because a standardised clinical protocol has yet to be developed. Regulations vary around the world. In the UK, for example, faecal transplants are not regulated. The US Food and Drug Administration has approved their use, but only for C. difficile infections.

At the same time, the number of people thought to be conducting their own faecal transplants at home is rising. Kelly advises against this, but Lawley points out that the area is impossible to regulate. “Faeces is not a drug or an organ – it’s shit,” he says. “You can’t control what someone does in their bathroom.”

Lawley hopes that the new case study will give people pause for thought. With recurrent C. difficile, the benefits are likely to outweigh any risks. But for other conditions, the picture is much hazier.

“Ultimately we’ll have to develop a well-defined group of bugs,” says Lawley, who is part of a team trying to identify the beneficial bacteria in faecal transplants. Other teams and companies are tackling the same problem. Allen-Vercoe is working with colleagues on a synthetic version of the faecal transplant – a tablet that contains carefully screened bacteria isolated from a healthy donor’s stools.

Until then, however, people considering faecal transplants for conditions other than C. difficile may want to reconsider their options. “People need to be aware of the risks,” says Allen-Vercoe.

“It sounds ridiculous, but we can expect celebrities to start selling their own faecal samples”

Read more: “Donors wanted: your bodily waste could be a big earner“

This article appeared in print under the headline “Don’t give me that crap”