Metabolic response to cottage cheese or egg white protein, with or without glucose, in type II diabetic subjects

Test meals with 25 g protein in the form of cottage cheese or egg white were given with or without 50 g glucose to male subjects with mild to moderately severe, untreated, type II diabetes. Water was given as a control meal. The glucose, insulin, C-peptide, alpha amino nitrogen (AAN), glucagon, plasma urea nitrogen (PUN), nonesterified fatty acid (NEFA), and triglyceride area responses were determined using the water meal as a baseline. The glucose area responses following ingestion of cottage cheese or egg white were very small compared with those of the glucose meal, and were not significantly different from one another. The serum insulin area response was 3.6-fold greater following ingestion of cottage cheese compared with egg white (309 v 86 pmol/L·h). The simultaneous ingestion of glucose with cottage cheese or egg white protein decreased the glucose area response to glucose by 11% and 20%, respectively. When either protein was ingested with glucose, the insulin area response was greater than the sum of the individual responses, indicating a synergistic effect (glucose alone, 732 pmol/L·h; glucose with cottage cheese, 1,637 pmol/L·h; glucose with egg white, 1,213 pmol/L·h). The C-peptide area response was similar to the insulin area response. The AAN area response was approximately twofold greater following ingestion of cottage cheese compared with egg white. Following ingestion of glucose, it was negative. When protein was ingested with glucose, the AAN area responses were additive. The glucagon area response was similar following ingestion of cottage cheese or egg white protein. Following glucose ingestion, the glucagon area response was negative. Glucose coingestion had a modest effect on the glucagon area response to cottage cheese (∼20% decrease), but markedly attenuated the response to egg white. The amount of ingested protein metabolized was calculated using the change in PUN concentration and the amount of urea nitrogen excreted in the urine. Following ingestion of cottage cheese it was 81%, and for egg white it was 52%. Ingestion of glucose with cottage cheese reduced the amount metabolized and attributable to urea formation to 56%. Coingestion of glucose reduced the amount of egg white metabolized to just 12%. In conclusion, the metabolic response to two common dietary proteins was very different. Coingestion of glucose with these proteins resulted in decreased urea formation. A close correlation was observed between the amount of protein metabolized and the glucagon area response (r = .94). Thus, the amount of ingested protein metabolized may be mediated, at least in part, by the circulating glucagon concentration.