Six adults with severe peanut allergies showed marked improvement after swallowing capsules containing healthy donor feces, suggesting gut microbes may hold the key to treating food allergies.
By Adam Makins · 
Imagine swallowing 36 capsules and four months later being able to safely eat a handful of peanuts when even a trace amount once sent you to the emergency room. For six adults in a Boston Children’s Hospital trial, this wasn’t science fiction. It was reality.
These participants had severe peanut allergies that triggered immediate reactions like hives and lip swelling from even minuscule amounts. After consuming capsules containing the fecal matter of a healthy donor with no food allergies, they experienced remarkable tolerance improvements. One participant could eventually handle the equivalent of four whole peanuts without incident.
“These responses represent a marked improvement,” says Rima Rachid, who led the research. The finding suggests that food allergies may be fundamentally linked to what lives in our guts, and that we might be able to fix them by importing better microbes from healthier people.
This trial adds compelling weight to a growing body of evidence linking food allergies to an imbalanced gut microbiome. When researchers transplanted fecal samples from the participants who responded well into mice, something remarkable happened. The mice’s guts saw a thousand-fold increase in Bacteroidales bacteria. Previous research has consistently shown that people with peanut allergies tend to have lower levels of these protective bacteria.
The mechanism isn’t fully understood yet, but the pattern is undeniable. A study of 1,400 Canadian children found peanut allergy correlated directly with low Bacteroidales levels. When Rachid’s team treated allergy-prone mice with these same bacteria, it prevented food allergies from developing entirely.
But here’s the catch: this was a small, open-label study where everyone knew they were receiving treatment. Skeptics like John Ziegler at the University of New South Wales correctly point out that placebo effect could explain some of the improvement. That’s why the team is now running a larger, randomized trial in children aged 12 to 17, comparing the faecal capsules against a placebo. A proper controlled study will finally tell us whether this treatment actually works.
Current peanut allergy management is frankly exhausting. People must obsessively avoid any peanut contamination and carry an EpiPen everywhere. Oral immunotherapy, which involves eating gradually increasing amounts of peanut powder over months or years, works for some but feels like a burden to many. Worse, its protective effects disappear once you stop the treatment.
The promise of a single day of capsule treatment that provides lasting protection, even if temporary, is genuinely exciting. Though participants still need to avoid peanuts and carry their EpiPens until we understand how long the effect lasts, the potential is undeniable.
Side effects from the capsules were mild and short-lived, mostly mild diarrhoea or abdominal pain. Faecal capsules have already proven their worth treating other conditions like ulcerative colitis and auto-brewery syndrome. They’re also far more practical than traditional microbiome transplants, which require uncomfortable tube insertion into the digestive system.
Rachid and her team are clear that we’re still in early days. The larger randomized trial will reveal whether the results hold up under proper scientific scrutiny. They’re also working to understand exactly why Bacteroidales bacteria provide protection.
If this treatment proves effective in children, we could be looking at a revolution in how we manage food allergies. Instead of a lifetime of anxiety and restriction, patients might receive a simple, one-day intervention. The fact that such a straightforward biological mechanism, your gut bacteria, might control something as serious as life-threatening allergies suggests we’ve barely begun understanding what our microbiomes really do.
Science Translational Medicine, New Scientist
