Fecal transplant increases tolerance to peanuts sixfold in small food allergy trial

Research Fecal transplant increases tolerance to peanuts sixfold in small food allergy trial By Marissa Russo Aug 5, 2026 2:00pm peanut allergy fecal transplantation microbiome Biotech Fecal transplants can increase tolerance to peanuts sixfold in people with food allergies, new research out of Boston Children’s Hospital has suggested. In the study, published Wednesday in Science Translational Medicine, responders showed tolerance to peanuts increased by up to 600 mg of peanut protein—roughly equivalent to nearly three peanuts compared to less than half a peanut at baseline—up to four months after fecal transplantation. The open-label, two-part phase 1 trial conducted at Boston Children’s Hospital, enrolled 15 adults and was designed to assess the safety and efficacy of oral encapsulated fecal microbiome transplantation (FMT).

FMT is an FDA-approved treatment for Clostridioides difficile infection and has a safe profile with a high cure rate. Lead study author, Rima Rachid, M.D., director of allergen immunotherapy at Boston Children’s Hospital, noted that although the food allergy study was very small, “there is an urgent, unmet need for disease-modifying therapies in food biology, and the microbiome offers a very interesting approach.” The microbiome is the body’s invisible gut garden that can grow bacteria, viruses and fungi. In recent years, researchers have become increasingly interested in understanding the components of the microbiome and reprogramming it to treat disease.

One way to reprogram the microbiome is via fecal transplantation from a healthy donor. This has been done safely in adults through colonoscopy, enema, or by running a tube through the nose to the gut, explained Rachid. More recently, researchers have been exploring oral capsule fecal transplantation for diseases such as fibromyalgia.

In the study at Boston Children’s Hospital, the researchers trained healthy donors to avoid peanuts and tree nuts leading up to donation of healthy stool. The samples were then processed, purified and packaged into odorless and tasteless oral capsules. Participants were tested at baseline using a food challenge test, and all reacted to less than 100 mg of peanut protein—roughly equivalent to less than half a peanut.

The first part of the trial included 10 patients who received a total of 36 FMT capsules. The second part of the trial included five patients who were dosed with the capsules following antibiotic pretreatment, to investigate whether this pretreatment improved the efficacy of the FMT capsules. Of all 15 treated participants, no adverse events of grade 3 or higher were observed, but five experienced either grade 1 or 2 side effects such as fatigue, diarrhea or headache.

An increase in peanut tolerance was seen in three of the 10 non-pretreated patients and three of the five pretreated participants. These increases were seen in as little as one month post-treatment and as long as four months, trends that are not achievable with other standard-of-care therapies for food allergy such as FDA-approved oral immunotherapy, where most patients see relapse once stopping treatment. Since they were unable to see significant differences in microbiome changes in responders compared to non-responders, the researchers decided to transplant the stools of these two groups into mice.

Mice that received fecal transplantation from human responders were protected from anaphylaxis and showed increased colonization of good gut bacteria called bacteroides. Additionally, in both humans and mice, there was an increase in bile acid metabolites in those protected from anaphylaxis, suggesting that this mechanism is mediated by the bile acid pathway, Rachid explained. “We are very excited about this,” she told Fierce.

“It's promising as a phase 1 trial, and we're currently conducting a phase 2 trial.” peanut allergy fecal transplantation microbiome Biotech Research