Peanut allergies might be treatable by using a fecal transplant to introduce “good” bacteria into a person’s digestive tract, a new study says.
Some young adults with peanut allergies wound up with a higher tolerance to peanuts months after receiving a fecal transplant from a healthy donor without food allergies, researchers reported Aug. 5 in Science Translational Medicine.
“This landmark study was the first to demonstrate that a microbiome-based therapy may improve food allergy in people while also revealing how gut bacteria, their metabolites and the immune system work together to influence treatment response,” lead researcher Dr. Rima Rachid said in a news release. She’s director of the Food Allergy Program and Allergen Immunotherapy Program at Boston Children’s Hospital.
“Larger studies of fecal and microbiota transplantation are now essential to confirm these findings, identify the patients most likely to benefit and discover beneficial bacteria that could be developed into targeted probiotic therapies for food allergy,” Rachid said.
About 8 percent of children and nearly 11 percent of adults in the U.S. suffer from food allergies. Currently, there are not many effective treatments for food allergies.
“People with food allergies want freedom from constant anxiety and extreme vigilance and to not have to be on guard for potentially dangerous exposures every time they leave the house,” Rachid said. “Patients don’t want therapies that have to be taken indefinitely and instead are looking for a permanent disease modification or cure.”
Earlier lab studies have shown that fecal transplants could protect mice from allergic reactions. Researchers thought that “good” bacteria found in healthy guts were responsible for this protection.
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For this new small-scale trial, the research team used frozen “poop pills” to transfer good bacterial strains into 10 young adults with severe peanut allergies.
After a one-time treatment of 36 pills taken over a few hours, three of the participants could tolerate eating multiple peanuts in an allergy challenge four months later.
The trial next tested whether antibiotics taken before the fecal transfer could help the body better “accept” the donor bacteria. In that step, 3 out of 5 participants improved in peanut tolerance, ingesting more than four peanuts before developing an allergic reaction.
Analysis of blood samples showed that people who responded to the therapy had higher bile salt levels than those who did not, researchers said.
Bile salts are made in the liver, stored in the gallbladder, and released into the small intestine to help break down fats for digestion.
The good bacteria from fecal transplants appeared to be better at using bile salts. By using bile salts, the new bacteria increased levels of immune regulatory cells that protect against allergic reactions, researchers said.
“Food allergy reflects a failure of oral tolerance, the process by which the gut immune system learns to accept food, and what this study shows is that the right bacteria can help restore that process, working through bile acid metabolites to promote the immune cells that enforce tolerance,” said senior researcher Dr. Talal Chatila, director of translational immunology at Boston Children’s Hospital.
“Knowing how the bacteria restore tolerance to food in allergic individuals allows us to optimize the therapy for more effective outcomes,” Chatila added in a news release.
Researchers next plan to try the treatment in teenagers, who will take their transplant pills from home under medical supervision. They’ll then be tested to see if they’ve become more tolerant to peanuts.
This study offers a very interesting new approach to peanut allergy. However, the results cannot yet tell us whether the treatment works equally well across racial and ethnic groups.
The Phase I study involved only 15 participants, so it is far too small to draw conclusions about differences by race or ethnicity. This factor is particularly important because Black patients have historically been underrepresented in food-allergy treatment research. A review of 26 food allergy immunotherapy trials found that Black participants only represented 8 percent of identifiable participants, compared with 72 percent who were white, despite evidence of a significant food allergy burden among Black communities.
This study highlights an ongoing issue with medical research: a promising treatment is only truly promising if researchers study it in everyone.
Diversity in clinical trials is critical because treatments may not affect every patient population in the same way. Including people from different racial and ethnic backgrounds helps researchers understand how safe and effective an intervention is across populations, and can help ensure that promising treatments are accessible and appropriate for everyone.
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The fecal-transplant study is a great early step, but it is not a cure for peanut allergies, nor is it clear who exactly will benefit. For Black patients and other groups historically underrepresented in food allergy research, ensuring diverse participation in future clinical trials will be critical for determining whether microbiome-based treatments can safely and effectively serve everyone.
More information
The American Academy of Allergy, Asthma & Immunology has more on peanut allergy.
SOURCE: Boston Children’s Hospital, news release, Aug. 5, 2026
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