Colonic bacteria ferment nutrientsescaped digestion and absorption in the small intestine to getenergy for their proliferation, and result in luminal accumulationof their fermentation products. Colonic fermentation and theirproducts are influenced by available substrates which vary chemicalcompositions and physical states. Plant fibers, resistant starch,nondigestible oligosaccharides and resistant proteins are principalsubstrates for colonic bacteria, and are anaerobically metabolizedto various organic acids, mainly short-chain fatty acids (acetate,propionate and butyrate), ammonia and amines. Short-chain fattyacids are rapidly absorbed across colonic mucosa and used as anenergy nutrient. Short-chain fatty acids, besides their energysupplier, play a role as luminal chemical stimuli that can modifyepithelial proliferation, intestinal blood flow, motility andsecretion. The effects vary among short-chain fatty acids, and aredose-dependent. The sensory mechanism, therefore, of thegastrointestinal tracts must be able to detect not only thepresence of individual short-chain fatty acids, but also theirconcentration.
Key words: colonic bacteria, nondigestible carbohydrates,short-chain fatty acids, gut function |
