Effect of sulfur amino acid supplementation of raw soy flour on the growth and pancreatic weights of rats.

Rat feeding studies showed that L-cystine, L-cysteine, N-acetyl-L-cysteine and L-methionine enhance the nutritional quality of raw (unheated) soy flour as measured in rats by the protein efficiency ratio (PER). Pancreas weights of rats fed diets supplemented with sulfur amino acids were higher than those of rats fed unsupplemented diets. In some instances this increase resulting from nutritional improvement of the diet was relatively greater than that in total body weight. Explanations are offered for these effects in terms of the proposed biofeedback mechanism involving the gastrointestinal endocrine system and the hormone cholecystokinin. The observed stimulation of pancreatic growth by added sulfur amino acids may be closely associated with this pancreatic regulatory mechanism when activated in response to dietary trypsin inhibitors present in unheated soy protein. The extent to which pancreatic hypertrophy develops as a result of a given exposure to trypsin inhibitors may be limited when the total amount or quality of the protein in the diet is less than optimal.