Prebiotic Dietary Fibers Must Achieve a Threshold of Beneficial Gut Bacteria in Order to Prevent Adiposity and Fatty Liver in Rats Fed High Fat Diets.

Abstract

Introduction Prebiotic dietary fibers are dietary fibers that are highly fermented in the large intestine, produce beneficial changes in the gut microbiome, and impart a health benefit to the host. Using reactive extrusion, we have synthesized a novel dietary fiber that is an oligosaccharide of polymerized lactose, which we term polylactose. Here we report on two studies feeding polylactose to rats to determine its prebiotic potential. Methods In Exp. 1, the polylactose preparation contained 51% dietary fiber, 20% free lactose, 5% glucose, and 24% other materials. Rats were fed high fat diets containing 9% total dietary fiber, including cellulose (C, 9%), polylactose (PL, 6%), polydextrose (PD, 6%), and fructooligosaccharide (FOS, 6%). In Exp. 2, the polylactose preparation contained 75% dietary fiber, 9% lactose, 3% glucose, and 13% other materials. Rats were again fed high fat diets containing 9% total dietary fiber, including C (9%), polylactose (6% or 3%), PD (6%), and galactooligosaccharides (GOS, 6%). In both experiments, rats were fed for 10 weeks, then ceca (empty), cecal contents, livers, and epididymal fat pads were collected. Results In both experiments, final body weight and daily energy intake did not differ among the groups. In Exp. 1, feeding PL greatly increased cecum weight (an indicator of fermentation), cecal Bifidobacterium and Lactobacillus species abundance, increased cecal acetate and propionate, and reduced liver lipids and fat pad weight, compared to the HFC group. PD and FOS increased probiotic species and short chain fatty acids slightly (compared to HFC), but not to the same extent as PL, and neither PD or FOS reduced fatty liver or adiposity. In Exp. 2, 6% PL increased cecum weight relative to 3% PL, PD and GOS, all of which were greater than HFC. The cecal microbiome was similar among PL (both 3 and 6%), PD, and GOS, all of which differed from HFC. Liver lipids, fat pad weight, and body composition did not differ among any of the groups in Exp. 2. Conclusions The prebiotic activity of polylactose differed depending on the preparation, for unknown reasons. However, our results suggest there is a threshold of probiotic bacteria abundance that must be attained before beneficial effects are imparted on the host by prebiotics.