Dietary proteins have an insulinotropic effect and thus promote insulin secretion, which indeed leads to enhanced glucose clearance from the blood. In the long term, however, a high dietary protein intake is associated with an increased risk of type 2 diabetes. Moreover, branched-chain amino acids (BCAA), a prominent group of amino acids, were recently identified to be associated with diabetes. Observational data and intervention studies do not point in the same direction regarding the effect of protein intake on insulin sensitivity and diabetes risk. Therefore, the first aim of this review will be to discuss human studies addressing high dietary protein intake and insulin action, with special attention for BCAA. In the second part, we will highlight the (patho) physiological consequences of high-protein diets regarding insulin action, in particular the role of the mechanistic target of the rapamycin pathway.