Impaired fasting glucose (IFG) confers a high risk of progression to diabetes. Its pathogenesis has been an area of active investigation, with defects in insulin and glucagon secretion as well as insulin action likely to play a role. Several studies have suggested that the prediabetic and diabetic state are associated with alterations in circulating incretin concentrations. More recently, a large study of non-diabetic individuals demonstrated decreased GLP-1 concentrations after a glucose challenge in individuals with prediabetes but concluded that defects in GLP-1 secretion were unrelated to insulin secretion. In impaired glucose tolerance (IGT), defects in incretin-induced insulin secretion coexist with defects in glucose induced insulin secretion.