Wheat Dietary Fiber Effects on Gut Microbiota Selective Growth

<p dir="ltr">Gut microbiome modulation through dietary fibers has potential to alleviate or prevent community dysbiosis related to various disease states. Wheat fiber composition and form can have targeted effects on gut microbes, but factors that govern gut microbiota selectivity for intact fiber structures are poorly understood compared to extracted fibers. Through <i>in vitro </i>fermentation of wheat dietary fibers with fecal microbiota, I determined several important relationships. First, wholemeal flours from different wheat species selected for different bacterial taxa; more specifically, durum and emmer flours selected for <i>Bifidobacterium adolescentis</i>, durum and hard red flours selected for <i>Bacteroides cellulosilyticus</i>, and hard red flours were much less selective for genus <i>Parabacteroides</i> compared to other flours. Similar relationships with these bacterial taxa were observed when extracted arabinoxylans from these same wheat species were used as substrate in <i>in vitro </i>fermentations, suggesting the role of arabinoxylan within intact fiber structures. Next, wheat breads made from wholemeal flours milled under different conditions were fermented with fecal microbiota, though any milling effects were eclipsed by sourdough starter choice during breadmaking. Rye starter breads promoted stronger growth of <i>Parabacteroides </i>possibly due to lower branching of arabinoxylans whereas wheat starter breads promoted stronger growth of <i>Bifidobacterium</i> and <i>Blautia</i> likely due to lower fructan levels. Finally, individuals fed wheat and sorghum brans had increased relative abundances of bacterial taxa specific to bran type, which also competitively grew during <i>in vitro </i>fermentation. Bran consumption altered fermentation rates of brans <i>in vitro </i>suggesting changes to microbiome function and structure after habitual and targeted exposure to specific dietary fibers. In summary, these results demonstrate potential to control selective effects of wheat dietary fibers through cultivar selection, processing conditions, and incorporation with finished products and provide a novel framework to predict and test effects <i>in vivo.</i></p>