Abstract

Because of the generally more rapid amino acid absorption and lower osmotic pressure of small peptides compared with free amino acids, it has been suggested that 'elemental' diets should contain both small peptides and free amino acids as the nitrogen source. While studying protein hydrolysates intended for use in such diets we observed surprising differences in the absorption of amino acids, water, and Na+ during jejunal perfusion of partial enzymic hydrolysates of two proteins (lactalbumin and fish) which contained high and approximately equal amounts of their constituent amino acids in the form of small peptides. Total alpha amino nitrogen (alpha NH2N) absorption from the lactalbumin hydrolysate was greater, and individual amino acid absorption more even, than from equinitrogenous solutions of the fish protein hydrolysate, or from mixture of free amino acids simulating either hydrolysate. Net water and Na+ absorption occurred during perfusion of the lactalbumin hydrolysate, whereas net water and Na+ secretion occurred during perfusion of the fish protein hydrolysate. These differences were significant (P < 0.05 or less). As the differences between the hydrolysates are so marked, we conclude that it is unwise to assume that all protein hydrolysates are equally suitable for use in patients.