The beneficial effects of prebiotics on bowel health were thoroughly investigated. The aim of the study was to show prebiotic effects of polydextrose (PDX). A placebo-controlled, randomized intervention study with PDX supplementation (8 g/day) was conducted in 45 healthy subjects. The effects of PDX on stool weight, orofaecal transit time, consistency of stool (Bristol stool form scale), short-chain fatty acid production, pH value, neutral sterol and bile acid excretion and faecal microbiota were evaluated. It was found that supplementation of PDX shortened the orofaecal transit time significantly. Furthermore, ingestion of PDX resulted in a decreased pH value and in significant changes in bile acid and neutral sterol excretion. PDX had no effects on stool weight, concentrations of the main short-chain fatty acids (acetate, propionate) and faecal contents of lactic acid bacteria and bifidobacteria. In conclusion, PDX is able to shorten the orofaecal transit time and to improve stool consistency in subjects suffering from constipation. [corrected]