Researchers have found an unexpected ally for protecting the body against the flu: dietary fiber.

Want to avoid the flu? Eat more fiber, a new study suggests.

More and more research is showing just how important our diet is for preventing a number of diseases and health conditions. It’s not just about straightforward problems, like diabetes or cardiovascular diseases — sometimes the prevention effect can be rather surprising. In this case, it seems that dietary fiber can blunt excessive and harmful immune responses in the lungs, while at the same time boosting antiviral immunity by activating T cells. This whole process is mediated by changes in the composition of gut bacteria.

“The beneficial effects of dietary fiber and SCFAs on a variety of chronic inflammatory diseases, including asthma and allergies, have received substantial attention in recent years and have supported momentum toward their use in clinical studies,” says senior study author Benjamin Marsland of Monash University. “But we were concerned that these treatments might lead to a general dampening of immune responses and could increase susceptibility to infections.”

Influenza, commonly known as “the flu”, affects millions of people every year, being one of the most common viral infections in the world. Aside from being extremely unpleasant, influenza can also be dangerous — and in some cases, fatal. Finding a way to boost immunity through diet alone would be a valuable tool for public health.

Dietary fiber is essentially the indigestible portion of food derived from plants. Although we don’t digest it directly, we can still draw a number of very important benefits from them. Dietary fiber helps keep our digestive system healthy, fighting obesity and severe diseases such as bowel cancer. It generally does this by keeping your gut bacteria healthy, but in the case of influenza, it’s a bit strange: the fiber seems to selectively turn on some parts of the immune system while switching others off — both to positive effect.

“We typically find that a certain treatment turns our immune system either on or off,” Marsland says. “What surprised us was that dietary fiber was selectively turning off part of our immune system, while turning on another, completely unrelated part of our immune system.”

This study also suggests that the so-called Western diet (high in sugars and fats, low in fiber) increases susceptibility to inflammatory diseases while decreasing protection against infections, something which has already been confirmed.

However, this study has only been carried out on mice. There’s a good chance the results will carry over to humans (something which researchers will test in the near future), but it remains to be seen if this is the case. At any rate, adding more fiber to your diet is always recommended, and will almost certainly provide significant health benefits.

Journal Reference: Immunity, Trompette and Gollwitzer et al.: “Dietary Fiber Confers Protection against Flu by Shaping Ly6c- Patrolling Monocyte Hematopoiesis and CD8+ T Cell Metabolism” http://www.cell.com/immunity/fulltext/S1074-7613(18)30191-2