INSR and type 1 diabetes mellitus: Procyanidin polyphenol type-A polymers extracted from cinnamon stimulate the autophosphorylation of the insulin receptor and inhibit protein tyrosine phosphatase I. Autophosphorylation of the insulin receptor kinase and the subsequent phosphorylation of its principal substrate were found to be decreased or inhibited in the insulin-responsive tissues of obese or non-insulin-dependent diabetes subjects [39, 40].