1. Small-intestinal absorption and permeability were measured in nine patients with malnutrition who were receiving liquid enteral nutrition after different periods of starvation, in five patients receiving enteral nutrition without starvation, in six healthy subjects after starvation for 36 h and in two obese subjects starved for 11 days.
2. Absorption, expressed by the plasma 60 min d-xylose level and the plasma 60 min d-xylose/3-O-methyl-d-glucose ratio, was greatly decreased (P < 0.001) in the nine patients receiving enteral feeding after starvation, whereas permeability, denoted by the 5 h urinary lactulose/rhamnose ratio, was increased (P < 0.05).
3. The five patients receiving enteral feeds without prior starvation had normal intestinal absorption and permeability.
4. Starvation of the healthy subjects reduced absorption (P < 0.05) and this was detectable at 36 h. Permeability, however, was not increased by 36 h starvation. Starvation of the obese subjects also progressively reduced absorption, and this was reversed with refeeding.
5. Changes in intestinal function during enteral feeding are similar to those seen in intestinal diseases. They develop rapidly and are not caused or reversed by liquid enteral feeds. Starvation, before beginning feeding, may explain some of the changes found.