According to a new preclinical study by researchers from the University of Lausanne and Monash University, a diet rich in fiber blunts harmful immune responses in the lungs while boosting antiviral immunity by activating T cells; and these dual benefits are mediated by changes in the composition of gut bacteria, leading to an increase in the production of short-chain fatty acids through the microbial fermentation of dietary fiber.
“The beneficial effects of dietary fiber and short-chain fatty acids (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,” said senior author Dr. Benjamin Marsland, from the Faculty of Biology and Medicine at the University of Lausanne and the Department of Immunology and Pathology at Monash University.
“But we were concerned that these treatments might lead to a general dampening of immune responses and could increase susceptibility to infections.”
From a public health perspective, influenza A infection is especially relevant because it is one of the most common viral diseases worldwide. Up to 20% of people are infected each year, resulting in substantial morbidity and mortality.
In the new study, Dr. Marsland and colleagues found that mice were protected from influenza infection by a diet supplemented with either the highly fermentable fiber inulin or SCFAs.
Specifically, these treatments led to both the dampening of the innate immune response that is typically associated with tissue damage, and also the enhancement of the adaptive immune response that is charged with eliminating pathogens.
“We typically find that a certain treatment turns our immune system either on or off,” Dr. Marsland said.
“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.”
Taken together with past studies, the team’s findings suggest that the modern Western diet consisting of food high in sugar and fat and low in fiber could increase susceptibility to inflammatory diseases while decreasing protection against infections.
From a therapeutic standpoint, additional research is needed to determine how much fiber, and what type of fiber, would be most effective in humans.
The study was published in the May 15, 2018 issue of the journal Immunity.
Aurélien Trompette et al. 2018. Dietary Fiber Confers Protection against Flu by Shaping Ly6c? Patrolling Monocyte Hematopoiesis and CD8+ T Cell Metabolism. Immunity 48 (5): 992-1005; doi: 10.1016/j.immuni.2018.04.022