Defined formula diets alter characteristics of the intestinal transport of amino acid and peptide in growing rats.

Recently defined formula diets are widely used for patients with digestive diseases. Long-term administration of such diets is presumed to change the absorptive characteristics of the small intestine. We investigated the influence of the defined formula diet on the absorptive capacity of growing rats by measuring the potential difference of sugars, amino acid, half-maximum concentration (kt) of these substrates, the activities of disaccharidase and dipeptidase, and the portal amino acid concentrations. There was no significant difference in the body weight of rats fed amino acid or peptide diets and those given the normal chow, but the administration of the defined formula diets reduced the absorption of amino acid and small peptide per serosal area and kt. On the other hand, absorption of sugars was not significantly influenced by the type of the diets. The differences in the absorptions of amino acid and peptide following the administration of the defined formula diet might be associated with the change in the resistance of the unstirred water layer or the alteration in the active transport system of amino acids or peptides in the small intestine. No significant differences were observed between the influences of the amino acid and the peptide diets.