Insulin Response to Ingested Protein in Diabetes

The ingestion of protein by normal human subjects has been shown recently to represent a stimulus to the secretion of insulin. This response is probably related to the postprandial rise in plasma amino acid concentration. Since disordered protein synthesis may contribute to the pathogenesis of diabetes and its complications, the insulin response to ingested protein (casein or gelatin, 50-100 gm.) was compared in twenty-eight normals and ten maturity-onset diabetics. Insulin response (microunits-minutes, μU.-min.) was considered to be the area included by that portion of the plasma insulin response curve above projected basal insulin secretion. Following protein ingestion the diabetics showed a mean insulin response (± S.E.M.) of 3,425 ± 367 μU.-min., compared with 1,005 ± 136 in the normals, a 3.4-fold difference (p < 0.01). In neither group were there significant or consistent changes in plasma glucose concentration. The fall in free fatty acids was comparable and no difference was seen in the plasma amino acid nitrogen curves. These data indicate that the insulin response to ingested protein is excessive in diabetes. The mechanism of the hyperresponse would seem to lie within the beta cell since no abnormality of the presumed amino acid stimulus was demonstrated.