CEREAL BRAN FIBER CONTROLS ON GUT MICROBIOME DIVERSITY, METABOLIC FUNCTION, AND HOST PHYSIOLOGY

Low gut microbiota diversity is associated with multiple chronic disease states, including metabolic syndrome and type II diabetes. Westernization of diet is strongly correlated with lower gut microbiome diversities compared with indigenous diets. Recently, many research groups have determined that: 1) loss of diversity is linked to consumption of the high-fat, low-fiber Western diet, and 2) in mice, these extinctions compound irrevocably over generations. Although cereal brans are rich sources of dietary fiber carbohydrates, a large percentage of brans are efficiently removed from human food streams by modern processing1. This results in large volumes of low-value waste brans2,3 that are available for use in dietary strategies to reduce chronic disease; however, we lack generalizable principles that link bran fibers with their fermenting microbiota and metabolic fates across highly-variable individual microbiomes.The long-term goal of this project is to develop a rational framework for use of cereal brans and their component fibers to maintain gut microbiome diversity and function. Remarkably little is presently known about how different dietary fiber structures interact with the gut microbiota. Preliminary studies in our laboratories have revealed that even subtle differences in bran carbohydrate structures are fermented divergently by microbiota. Specifically, our data suggest that: 1) fermentation of otherwise-identical wheat bran particles differing in size results in distinct microbiota compositions and metabolic function, 2) each cereal bran selects for different species from the same initial pool of microbiota, 3) fine structural differences in wheat bran arabinoxylans (AXs, dietary fiber polysaccharides) determine the rate and outcome of microbial fermentations, and 4) sorghum AX (SAX) selects for, and stably maintains, a consortium of fermenting fecal microbiota species in a non-competitive manner. Taken together, these data suggest that differences in bran type, processing, and their constituent AX structure may exert significant impacts upon gut ecology and function. From these data, we propose our central hypothesis: that seemingly-minor physical and chemical differences in bran fiber structure due to cereal type or processing will favor distinct microbial species and govern metabolic outcomes.We propose to test this hypothesis by systematically linking bran fiber structure and processing methods with microbial species and metabolic outputs through the following objectives:Quantify the impacts of whole cereal bran type, particle size, and milling methods on the diversity, composition and metabolic function of gut microbiota in vitro.Quantify the impact of soluble bran arabinoxylan chemical structure on diversity, composition and metabolic function of gut microbiota in vitro.Evaluate the in vivo effect of bran fiber structure on gut microbiome structure and function.This proposal is highly responsive to USDA Improving Food Quality program area goals by increasing mechanistic understanding of how brans, bran processing, and soluble bran fibers impact the gut microbiome and, in turn, influence nutritional outcomes and overall host physiology. We expect to generate fundamental knowledge that will enable use of bran fibers in dietary strategies for targeted improvements in gut microbiome composition and function with the goal of improving nutritional benefit and reducing chronic disease burdens.