1. The hypothesis that triacylglycerols are trophic to the small-intestinal mucosa of the rat was tested by comparing the action of the essential fatty acid-rich oil Efamol with that of glucose.
2. Two groups of nine female Wistar rats were pair-fed Vivonex HN with 50% calorie substitution by glucose or Efamol for 21 days.
3. Body weight gain was greater with glucose than with Efamol, but, despite this, whole gut weight, mucosal weight and mucosal protein were increased by Efamol in all small-intestinal segments. Total mucosal DNA was also increased with a significant change in the middle small-intestinal segment. These changes were associated with an increased crypt cell production rate.
4. Fasting plasma levels of peptidyltyrosyltyrosine (‘peptide YY’), but not of enteroglucagon, were significantly elevated in the Efamol-fed group.
5. The data show a trophic effect of Efamol on the rat small-intestinal mucosa. Possible mechanisms are discussed.