Dietary fibers differentially alter host immunity via gut microbial metabolism

Although correlations between certain gut microbial taxa abundance and inflammation have paved the way to microbiome research in health and disease, the functionality of microbes through their metabolism in the context of host immunity remains to be elucidated. Given that dietary fibers are considered highly beneficial for health but exclusively fermented by the microbiota, we utilized distinct rodent diets with a focus on both fiber content and source to understand their functional impact on host immunity through the microbiome metabolism. We show that during fiber deprivation, the metabolic capacity of the microbiome decreases; namely, microbial B vitamins, short-chain fatty acids and polyamine metabolite production is halted, while pro-inflammatory medium-chain fatty acids are increased. Using mass cytometry time-of-flight (CyTOF), we identify that this metabolic shift coincides with increased effector cell populations and activated T cells within the gut immune landscape of fiber-deprived mice. Supplementation with inulin, but not diverse crude fiber sources, can recover the metabolic capacity and immune homeostasis lost during fiber-deprivation. Taken together, we have found that high fiber and inulin-suppplementation are able to harness a microbiota with a beneficial metabolic capacity and immunotolerogenic environment. These data represent the potential for fiber source to better target a healthy immune environment.

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