**3.3 Amino acid stimulated insulin secretion**

At individual concentrations amino acids found in physiological concentrations are poor insulin secretagogues. Some combinations of amino acids at physiological concentrations are capable of enhancing GSIS [37], like that of, glutamine cannot stimulate insulin secretion or enhance GSIS alone, but in combination with leucine, glutamine is capable of stimulating insulin secretion from β-cells and enhancing GSIS [38]. Leucine activates glutamate dehydrogenase, and glutamate dehydrogenase can convert glutamate to α-ketoglutarate, leading to production of ATP and stimulating insulin secretion [37]. Two important incretin hormones secreted from K-cells and L-cells in the gastrointestinal tract, Glucose dependent insulinotropic peptide (GIP) and glucagon-like peptide-1 (GLP-1), are stimulated to be secreted after ingestion of nutrients like glucose and amino acids. These hormone levels rise in the circulation after feeding food rich in protein and carbohydrates. Then they directly trigger insulin secretion from β-cells by binding to their specific cell-surface receptors, hence enhancing GSIS [39–41].
