When Andrew Koh started studying why some gut bacteria help fight off dangerous fungi, he noticed something strange: patients whose microbiomes had been disrupted by cancer treatment or heavy antibiotics were far more likely to get sick from fungal infections. Now, his team at UT Southwestern Medical Center in Dallas has discovered exactly why—and how a common fiber in your diet might help.
In a study published in the journal Cell Host & Microbe, Koh and his colleagues found that friendly gut bacteria produce acids called short-chain fatty acids, or SCFAs, when they digest dietary fiber. These acids appear to shield the gut from Candida albicans, a fungus that lives naturally in our intestines but can cause deadly infections when it grows out of control.
The team tested three of these fatty acids—butyric acid, propionic acid, and acetic acid—on Candida growing in lab dishes. The more acid they added, the slower the fungus grew. Butyric and propionic acids were especially effective at putting the brakes on Candida.
Curiously, the acids worked by attacking the fungus's ability to eat. They blocked Candida from absorbing glucose, disrupted how it digests nutrients, and made the inside of fungal cells more acidic. Each of these small disruptions added up, slowing the fungus until it couldn't overtake the other gut microbes.
To see if this might work in living animals, the researchers gave SCFAs to mice carrying Candida. The treatment worked much better in mice with normal gut bacteria than in mice raised without any gut microbes at all—a sign that the fatty acids depend on existing friendly bacteria to do their job. When the team gave mice bacteria that had been engineered to stop producing these acids, the treatment became less effective, confirming that both the bacteria and their fatty acid products matter.
Most promising of all, the scientists created a molecule that links a type of fiber called inulin to propionic acid. When gut bacteria digest this combination, they release the protective acid right where Candida lives. In mice, this treatment significantly reduced fungus levels in the intestines.
The findings could eventually help protect patients at highest risk: those undergoing cancer therapy, stem cell transplants, cellular therapy, or long courses of antibiotics—all of which can throw off the balance of gut bacteria and leave patients vulnerable to fungal infections that claim many lives each year.
Koh's team plans to keep studying exactly how these fatty acids fight Candida, with the goal of someday turning this discovery into dietary advice, probiotic treatments, or simple pills that could help vulnerable patients stay safe.