Determinants of decreased fecal consistency in patients with diarrhea

Loose stools are a common and troublesome feature in diarrhea. The purpose of this study was to investigate factors that determine different degrees of stool looseness in diarrhea.

Fecal consistency was measured visually. Stools were analyzed for content of water and solids. Water-holding capacity of insoluble solids was measured in vitro.

Formed stools from normal subjects had a near constant ratio of water to solids despite a sevenfold variation in daily stool weight. In diarrhea, loose consistency was correlated directly with percent fecal water. For any level of percent water, steatorrhea stools were looser than nonsteatorrhea stools. Ingestion of psyllium reduced stool looseness without changing the percent water. Both the effect of fat and psyllium could be explained by consideration of the ratio of fecal water to water-holding capacity of insoluble solids.

(1) The normal intestine delivers stools that differ widely in quantity but maintains percent fecal water within a narrow range. (2) Stool looseness in diarrhea is determined by the ratio of fecal water to water-holding capacity of insoluble solids. (3) In patients with diarrhea with normal stool weight, loose stools are due to low output of insoluble solids without the concomitant reduction in water output that occurs in normal subjects when insoluble solids are low.