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.