Popular fiber supplement may influence immunity beyond the intestines

New research indicates that inulin, a widely used fiber, may shape immune activity in the lungs as well as in the gut, according to experimental findings. The study suggests gut microbes can transform a dietary ingredient into signals that reach distant tissues, with effects that may be beneficial or harmful depending on the situation.

The finding is important because inulin is commonly added to supplements and fiber-fortified foods. A clearer understanding of its immune effects could help scientists design nutrition strategies more precisely, especially in studies of allergies, inflammation and the body’s defenses against infection.

At the same time, the result offers a more nuanced picture of how specific fibers function. It does not mean that everyday inulin-containing foods cause asthma in people, and it does not challenge the overall value of fiber in a balanced diet.

Researchers from Weill Cornell Medicine and the Boyce Thompson Institute reported the work in Nature in 2022. Using mice, they examined how an inulin-enriched diet changed gut microbes, their chemical byproducts and immune responses.

Inulin is a fermentable fiber, which means gut bacteria can break it down even though human digestive enzymes cannot fully do so. It occurs naturally in several plants and is also added to products designed to boost fiber intake or encourage beneficial microbes.

After two weeks on the inulin-rich diet, the mice showed increased eosinophils in both the gut and lungs. These white blood cells are linked to type 2 inflammation, a kind of immune response involved in reactions to parasites and allergens.

The researchers traced the effect to changes in how gut bacteria processed bile acids, which are compounds involved in fat digestion. Those chemical shifts activated pathways that pushed immune cells toward a type 2 response.

Additional experiments supported that explanation. When a bile acid receptor was removed, the inflammatory effect weakened, and blocking a bacterial enzyme involved in bile acid processing also prevented it, creating a clearer link among the fiber, microbes and immune signaling.

The outcome varied with the challenge facing the animals. Inulin intensified allergic airway inflammation in the experiment, but the same kind of immune activity also helped protect against parasitic worms, showing that a stronger response is not always simply good or bad.

The team also reproduced relevant effects in mice carrying human-derived gut microbes. That provides a useful step toward human research, but the animals were still mice, so it does not prove the same effects, doses or health outcomes in people who take supplements.

For readers, the study underscores the need to look at the specific properties of each fiber rather than assuming all fibers act the same way. Anyone concerned about an added-fiber product should discuss its ingredients and symptoms with a health professional, while human studies are still needed before drawing clinical conclusions from these immune findings.

If you are interested in this topic, please read articles about Prebiotic fiber could manage high blood pressure, and 8 natural ways to reduce inflammation.

For more information, please see articles about All about vitamin C: why we need it and how to get it, and Mediterranean diet could help prevent colon cancer, gut diseases.

Source: Weill Cornell Medicine; Boyce Thompson Institute.