Effect of Replacing Cellulose With Primarily Insoluble Fiber on the Microbiome and Short Chain Fatty Acids, and Fecal Calprotectin in Mice Fed a High Fat Diet

OBJECTIVES: Most semi-purified rodent diets contain only cellulose as the fiber source, and do not provide diverse fermentable substrates for the gut microbiota. The focus of this work was to determine how replacing cellulose with a mix of cereal fiber, pectin and beta-glucan affected the gut microbiota, short chain fatty acids, and fecal calprotectin in C57BL/6 mice. METHODS: Using a suggested, one day, adequate fiber human diet from the Institute of Medicine (IOM), the relative proportions of cellulose (57%), hemicellulose (20%), lignin (4%), pectin (15%) and beta-glucan (4%) were estimated using a food composition database. A combination of oat hull fiber, pectin and beta-glucan was added to a 45% kcal from fat rodent diet to provide these fiber sources at the typical US nutrient density (9g/1000 kcal), or at the IOM recommended level (14 g/1000 kcal). Mice were fed the experimental diets for 16 weeks. Cecal and fecal samples were collected at the end of the study and the microbiome was determined by 16S rRNA sequencing, short chain fatty acids by GC-FID, and fecal calprotectin by ELISA. RESULTS: There were no differences in weight gain, final weight, and lean mass, but for mice fed the low fiber diet there was a trend for lower % fat mass (p = 0.08). There were no differences in either alpha or beta diversity in the cecal or fecal microbiome samples. According to the Linear discriminant analysis Effect Size (LEfSe), at the genus level, the DIO diet was characterized by Lactococcus, the high fiber diet by Allobaculum, and the low fiber diet by Enterococcus. There were no significant differences in cecal SCFAs, but there was a trend for mice fed the high fiber diet to have more acetate (p = 0.053) and less isobutyrate (p = 0.06) and isovalerate (p = 0.07). There were no differences in empty cecum weight nor colon length. However, mice fed the low fiber diet had significantly more fecal calprotectin than mice fed the DIO or high fiber diets (p < 0.01). CONCLUSIONS: Adding a blend of purified fibers to the DIO diet resulted in few effects on the microbiome composition or metabolism. However, there was a trend for mice fed the higher fiber to have less body fat. In addition, increasing the fiber intake from typical US levels to those recommended by the IOM was associated with less gut inflammation, as measured by calprotectin. FUNDING SOURCES: Funded by the National Institute of Food and Agriculture.