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Metabolism. 2012 Dec;61(12):1696-702. doi: 10.1016/j.metabol.2012.05.008. Epub 2012 Jun 15.

Combining protein and carbohydrate increases postprandial insulin levels but does not improve glucose response in patients with type 2 diabetes.

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Medizinische Klinik und Poliklinik III, Justus-Liebig-Universität, 35392 Giessen, Germany.



A combined load of carbohydrate and protein stimulates insulin secretion. However, results on postprandial glucose responses in type 2 diabetic (T2D) subjects have been inconclusive. Therefore, we investigated the effects of co-ingestion of carbohydrate and protein on glucose and insulin responses in these subjects.


After an overnight fast, 30 subjects consumed a drink containing 50 g of slowly-digested isomaltulose (ISO), combined either with a mixture of 21 g whey/soy (ISO+WS) or with 21 g casein (ISO+C) in a randomized order on separate days. In another experiment, the subjects consumed a control drink containing only 50 g ISO.


No significant differences in glucose responses were observed after ingestion of the drinks. Compared to ingestion of ISO alone, insulin response was ~190%-270% higher (P<.001), whereas insulin action was lower (P<.01) after ingestion of ISO+WS and ISO+C. Plasma insulin levels increased more significantly (P<.001) after ingestion of ISO+WS compared to ISO+C and were positively correlated with total amino acid levels (P<.001). Insulin action, however, showed a greater decrease following ingestion of ISO+WS than ISO+C (P<.01).


Combining carbohydrate with protein can elevate postprandial insulin levels, but decreases insulin action, and therefore does not improve glucose response in T2D subjects. Our results further suggest that different types of proteins (i.e., fast-absorbing whey/soy vs. slow-absorbing casein) differently modulate insulin response and insulin action. A fast-absorbing protein mixture reduces insulin action to a greater extent than a slow-absorbing protein, and therefore may not be recommended for glycemic control in T2D patients.

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