Lactitol and Lactulose

Summary

Both lactulose and lactitol are nonabsorbable disaccharides. In an effort to determine similarities or dissimilarities in their effect on the normal human gut flora, parallel in vitro and in vivo experiments were carried out using pyxigraphy. Stools from healthy volunteers were used to determine pH, ammonia concentrations, and numbers of microorganisms in caecal contents and stool samples. There was a marked inhibition of ammonia production and a fall in pH, the latter depending on the concentration of sugar added in both in vitro and in vivo experiments. The numbers of aerobes and anaerobes in all suspensions fell, both in vitro and in vivo. The fermentation of the disaccharides by the most important intestinal microorganisms (in vitro) was also determined: all quantitatively important intestinal microorganisms fermented both disaccharides. Both lactulose and lactitol caused acid to form, and both reduced the formation of ammonia by selected bacteria. Lactitol and lactulose can, therefore, be regarded as similar in their mode of action on the normal human intestinal flora.