Do fecal transplants help irritable bowel syndrome?
No. In a large phase 3 trial, a one-time fecal transplant from a healthy donor worked no better than a transplant of a person’s own stool. At 90 days, 40% of the donor group and 38% of the placebo group had a meaningful drop in IBS symptoms.
Irritable bowel syndrome, or IBS, causes belly pain, bloating, diarrhea, constipation, or a mix of these. One popular idea is that IBS starts with the wrong mix of bacteria in the gut. If that were true, swapping in bacteria from a healthy person should help.
That swap is called a fecal microbiota transplant. Stool from a healthy donor is processed and placed into the patient’s colon, in this trial through a single enema. The goal is to reset the gut’s bacterial community. This trial, called REFIT2, set out to test whether a fecal transplant for IBS delivers on that promise.
What the data show
Researchers in Norway enrolled 450 adults with moderate-to-severe IBS. Two out of three got stool from a healthy donor. The rest got their own stool back, which served as the placebo. Success meant a drop of at least 75 points on a standard IBS symptom score by day 90.
In the donor group, 119 people (40%) reached that goal. In the placebo group, 57 people (38%) did. That is a gap of only 1.9 percentage points. The true difference very likely falls somewhere between 8 points worse and 12 points better than placebo, a range that includes no effect at all (95% CI -8.1 to 12.0). If the transplant did nothing at all, a gap at least this big would still show up about 3 times out of 4 by chance alone (p=0.76). Side effects were reported at similar rates in both groups.
Dr. Kumar’s Take
This is a clean, well-designed negative result, and negative results like this matter. The trial was large, randomized, and double-blind. Neither patients nor the staff treating and assessing them knew who got donor stool. That design is exactly what you need to separate a real effect from hope.
The most telling number is the placebo group. Nearly 4 in 10 people who got their own stool back felt meaningfully better. That is a big improvement for a treatment that changed nothing about their gut bacteria. It shows how easily an uncontrolled “gut reset” can look like it works.
The authors concluded that changing the gut bacteria alone might not be enough to improve IBS. I agree. IBS is more than a bacteria problem, and products sold as a fix for the gut microbiome deserve more skepticism after this trial.
Study snapshot
The trial ran at five hospitals in Norway. Researchers screened 2,304 people between May 2021 and July 2022. Everyone enrolled was 18 to 65 years old and met the standard Rome IV criteria for IBS. Each also scored 175 or higher on the IBS Severity Scoring System, the cut-off for moderate-to-severe disease.
Screening was careful. People 50 or older needed a colonoscopy within the past 5 years to rule out colon cancer. People with diarrhea-predominant IBS needed biopsies to rule out microscopic colitis, a different bowel disease that looks similar.
Of the 448 people analyzed, 65% were women. The median age was 36. Two enrolled people were left out of the analysis because their treatments were switched by mistake.
Safety, limits, and caveats
The good news is that the fecal transplant did not cause more side effects than placebo. The proportion of people with any adverse event was similar in both groups.
This trial tested one approach: a single enema, judged at 90 days. It does not test repeated transplants or delivery by other routes. It also enrolled adults up to age 65 in Norway, so it says less about older adults. Still, a single, well-run trial of 450 people is a strong answer to the question it asked.
Practical Takeaways
- A single fecal transplant from a healthy donor did not relieve IBS better than placebo in this trial, so it is not a proven IBS treatment.
- Be cautious with clinics or products that promise to “reset” your gut to cure IBS, since this trial found microbiome change alone may not be enough.
- Judge any IBS treatment against a placebo, since 38% of people in this trial improved meaningfully after receiving only their own stool.
- If you are 50 or older with bowel symptoms, make sure colon cancer has been ruled out, as this trial required a colonoscopy within 5 years for everyone in that age group.
Related Studies and Research
- Placebos helped older adults even when they knew the pill was fake
- Time-restricted feeding improves Crohn’s disease activity in a 12-week trial
- Single-dose psilocybin vs placebo: first double-blind depression trial
- Antidepressant weight gain: why it happens and how to prevent it
FAQs
Why did people who got their own stool improve?
Getting your own stool back does not change your gut bacteria, yet 38% of that group improved meaningfully. The trial was not built to explain why, but the placebo effect is the likely reason. Expecting relief from a procedure can change how symptoms feel. That is exactly why a placebo group matters: without one, the 40% response in the donor group would have looked like a success.
Is a fecal transplant for IBS safe?
In this trial, the share of people with side effects was similar in the donor group and the placebo group. That points to a single enema being well tolerated in the short term. Safety is only half the question, though. A treatment with no clear benefit is hard to justify, even when it causes few problems.
Does this mean gut bacteria have nothing to do with IBS?
Not exactly. The trial tested whether changing gut bacteria with one donor transplant relieves symptoms, and it did not. The researchers concluded that changing the gut bacteria alone might not be enough to improve IBS. Bacteria may still play some part, but they do not seem to be a simple switch that can be flipped to fix symptoms.
Bottom Line
A large, double-blind trial of 450 adults found that a single fecal transplant from a healthy donor relieved IBS symptoms in 40% of people, compared with 38% who received their own stool. That 1.9-point gap was well within the range of chance, and side effects were similar. For now, fecal transplants are not a proven treatment for irritable bowel syndrome, and “gut reset” claims deserve a hard look.
