Objectives: Grain-based diets (GBDs) are widely used in rodent studies, but the lack of control of ingredients in GBDs and potential batch to batch variation limit their utility. Purified diets (PDs)—diets with known sources and quantities of all nutrients—offer solutions and permit investigators to control for diet, a major environmental factor, in rodent studies. However, mice fed a standard PD display abnormal gastrointestinal (GI) anatomy and greater adiposity compared to mice fed a GBD—Purina 5001. Interestingly, the addition of a soluble fiber (inulin) to PDs (which usually only contain the insoluble fiber cellulose) ameliorates these adverse effects. Yet, the impact of PDs modified with soluble fibers from mixed sources on GI anatomy and the intestinal microbiota has not been investigated. We therefore sought to identify a combination of fibers in PDs 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 length, colon length, cecal weight, and colon weight 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 Quantitative Insights Into Microbial Ecology 2 pipeline (QIIME 2) pipeline.
Results: Consistent with published data, GI anatomy was altered in mice consuming PDs compared to GBDs. Microbiotas from mice fed any PD significantly differed from mice consuming either GBD in all GI niches (p<0.05, ANOSIM). Microbiotas were distinct between mice fed either Purina 5001 or Teklad 2020SX GBDs (p<0.01, ANOSIM). Mice fed low soluble fiber PDs (≤ 25% soluble fiber) also produced significantly different microbial communities than mice fed high soluble PDs (≥ 75% soluble fiber) (ANOSIM, p<0.001). Unexpectedly, the microbial richness of mice decreased with increasing soluble fiber content in PDs. The relative abundance of Lactococcus spp. and the [Eubacterium] xylanophilum group were different between mice fed GBDs and PDs, while Romboutsia spp. had a higher relative abundance in mice fed low soluble fiber PDs compared to other diet groups.
Conclusions: Mice fed PDs with high soluble fiber content (≥ 75% soluble fiber) best recapitulated GI health compared to mice fed GBDs. However, no PD tested recapitulated the microbiotas of mice fed GBDs. The creation of PDs with a mixture of soluble and insoluble fibers is highly desirable to improve reliability in future rodent studies regarding diets and gut microbiota.Bachelor of Science in Public Healt
