In a previous study, we have shown that whey protein
resulted in a higher insulin response than cheese (casein)
or milk (whey and casein), respectively [6]. The major
insulin releasing properties of milk could thus be
ascribed to the whey fraction, and the mechanism appears to be related to the specific amino acid pattern
appearing in postprandial blood after whey ingestion [6].
When administrated with carbohydrates, dietary amino
acids stimulate the insulin release from the pancreatic β-
cell [9]. Especially leucine (leu) is a known to be strong
insulin secretagogue [10]. Consequently, the lowering of
glycemia seen when adding whey to a carbohydrate containing
meal can to a large extent be mimicked by supplementation
of the meal with specific amino acids [11].
In addition, whey proteins appear to stimulate the incretin
hormones glucose-dependent insulinotropic polypeptide
(GIP) and glucagon-like peptide 1 (GLP-1) [12].
Both GLP-1 as well as GIP has been identified as strong
insulinotropic agents [13]. Furthermore, it has recently
been reported that dietary branched chain amino acids
(BCAA) facilitates GLP-1 release from intestinal-cells
[14]. Thus, plasma amino acids per se can possibly cause
an incretin secretion, and partly explain the reduction of
glycemia seen when adding whey to a carbohydrate containing
meal.