Effect of lactulose-derived oligosaccharides on intestinal microbiota during the shift between media with different energy contents.

The microbiological and metabolic changes of an overweight-associated colonic microbiota after reducing in vitro the carbohydrate supply and its supplementation with oligosaccharides derived from lactulose (OsLu) were evaluated using a dynamic simulator of the gastrointestinal tract. The differentiation and stability of the microbial communities within each colon compartment were reached after two weeks of feeding the system with a high energy (HE) medium based on fructose and readily fermentable starches. The effect of reducing the energy content (low-energy medium, LE) and the supplementation with OsLu caused minor variations in bacterial counts, except for Enterobacteriaceae. The LE medium caused an effect on the microbial metabolic activity that was characterized by an absence of net butyrate production and an increase in ammonium content. This shift from fermentative to proteolytic metabolism was not observed when the LE medium was supplemented with OsLu. This oligosaccharide mixture was mainly metabolized in the proximal colonic compartment. The results obtained in this study indicate that the substitution in the diet of easily digestible carbohydrates by OsLu maintains the fermentative functionality of the intestinal microbiota, allowing the net production of butyric acid with potential beneficial effects on health, and avoiding a full transition to proteolytic metabolism profiles.