Ingested protein provides substrate for gluconeogenesis and strongly stimulates insulin and glucagon secretion, but it has little effect on the glucose concentration in people with type 2 diabetes. Ingested fructose also is a substrate for gluconeogenesis, modestly stimulates insulin and glucagon secretion, and has little effect on the plasma glucose. Therefore we were interested in determining if ingestion of fructose along with protein would result in an additive, greater than additive, or less than additive effect on circulating insulin, glucagon, and glucose concentrations.
Seven male subjects with untreated type 2 diabetes were fasted overnight and then were given either 25 g fructose, 25 g protein, 25 g fructose plus 25 g protein, or water only at 0800. Subjects also ingested 50 g glucose on two separate occasions. Plasma glucose, insulin, C-peptide, glucagon, α-amino nitrogen, urea nitrogen, nonesterified fatty acids, and triglyceride concentrations were determined over the subsequent 5 h.
The glucose concentration was only modestly increased and the area responses were similar when protein, fructose, or the combination was ingested. Thus, the glucose response to the combination was less than additive. The insulin area response to protein was 2.5-fold greater than to fructose, and the response to the two nutrients was additive and quantitatively similar to the response to 50 g glucose. The glucagon area response was less than additive, i.e., there was an interaction between the protein and fructose that resulted in a smaller than expected response.
When protein and fructose were ingested together, the insulin response was similar to that following ingestion of 50 g glucose. It also was as expected based on the response to the individual nutrients. In contrast, the glucose and glucagon responses were significantly less than expected. These data may be useful in dietary planning for subjects with type 2 diabetes.