The Effect of Dietary Fiber Modifications in Purified Diets Relative to Grain-Based Diets on Gastrointestinal Anatomy and Intestinal Microbial Communities in Mice
Abstract Objectives The use of compositionally defined purified diets (PDs)—diets with known sources and quantities of all nutrients—permits investigators to control this major environmental factor in rodent studies. However, mice fed a standard PD exhibit abnormal gastrointestinal (GI) anatomy compared to mice fed Purina 5001, a grain-based diet (GBD). Interestingly, the addition a soluble fiber (inulin) to PDs (typically only containing cellulose, an insoluble fiber) ameliorates these adverse effects. The impact of PDs on the intestinal microbiota has not yet been investigated. We therefore sought to identify PD-supplemented fiber(s) that best recapitulate the GI health and intestinal microbiota of mice fed a GBD, while also including an additional reference GBD (Teklad 2020SX). Methods 7-week-old C57BL/6J male mice were individually housed and randomly assigned to a diet (two GBDs and four PDs with varying fiber composition) for 28 days. To assess changes in GI anatomy, small intestinal and colon lengths and colon and cecal weights were recorded at tissue harvest. Cecal contents, colon contents, and fecal pellets were collected for 16S rRNA gene sequencing to compare microbial profiles across different GI niches and between diets using the Divisive Amplicon Denoising Algorithm (DADA2) pipeline. Results Consistent with published data, GI anatomy was altered in mice consuming PDs compared to the Purina GBD. However, there were no significant anatomical differences between mice consuming PDs and the Teklad GBD. Characterization of microbial communities revealed that the GI niche (cecum, colon, or feces) dictated microbial composition (P < 0.001, ANOSIM). Microbiotas from mice fed any PD significantly differed from mice consuming either GBD (P < 0.05, ANOSIM). Microbiotas were also distinct between mice fed either Purina 5001 or Teklad 2020SX (P < 0.01, ANOSIM). Conclusions These data suggest that Purina 5001 does not represent all GBDs and that PDs may not significantly alter rodent GI anatomy compared to GBDs. As each diet tested significantly altered the microbial community, future work will seek to determine whether a specific PD-associated gut microbiota is beneficial to GI health. Funding Sources The NIH, the Honors Carolina Sarah Steele Danhoff Undergraduate Research Fund, and Research Diets, Inc.
