FAMINE, FIBER, FATTY-ACIDS, AND FAILED COLONIC ABSORPTION - DOES FIBER FERMENTATION AMELIORATE DIARRHEA

The salvage function of the colon for absorption of unabsorbed sodium and water from the jejunum and ileum depends upon the metabolic integr ity of colonic epithelial cells maintained by luminal short-chain fatt y acids. With the depletion of luminal short-chain fatty acids under c onditions of starvation, metabolic compensation from vascular substrat es is incomplete. Loss of luminal short-chain fatty acids diminishes c ell membrane integrity and causes secretion by colonic epithelial cell s, leading to starvation diarrhea. Because sodium absorption is depend ent upon CO2 production from n-butyrate, no compensatory absorption oc curs during starvation. Under conditions in which luminal short-chain fatty acids are depleted, dietary fiber is useful as a low osmolality food constituent and for renewal of short-chain fatty acid levels by b acterial fermentation. The ''antisecretory'' effect of dietary fiber d epends on the degree of the preexisting depletion of short-chain fatty acids and the methodology used to assess absorptive function. Dietary fiber has not been found harmful in refeeding starvation victims for whom it is an essential food constituent.