Endogenous gut signals and metabolites control daily food intake.

Parabiotic pairs of inbred Lewis rats had two different types of crossed intestinal surgery performed. In the one-way surgery, food was lost from the duodenum of one rat in a pair into a 30 cm segment of upper small intestine of its partner. The unabsorbed intestinal chyme returned to the lower duodenum of the first rat. In the second surgery, food was lost from the lower jejunum of one rat into the upper ileum of its partner. The lower gut of the first rat received no further food stimulus while the ileum, cecum and colon of its partner were doubly stimulated. As a result of these two surgeries, the rat in each pair that lost food into its partner's intestine showed a 40-60 percent increase in daily food intake while its partner reduced its intake by an equivalent 40-60 percent regardless of whether the food was lost into the upper or lower small intestine. The large and sustained changes in daily food intake did not correlate significantly with body weight or with the wet weight of the fat, liver or heart at sacrifice. Therefore, daily significant changes in body or organ weight were not necessary to produce large changes in daily food intake. Instead, some combination of endogenous signals from the gut, of plasma levels of absorbed nutrients or of endogenous signals generated by the subsequent metabolism of absorbed nutrients in peripheral tissues must control daily food intake.