Glucagon-like peptide 1 concentrations during oral glucose tolerance tests in different metabolic conditions. Mean fasting and postprandial values of participants with normal glucose tolerance, impaired glucose tolerance, isolated impaired glucose tolerance, impaired fasting glucose or isolated impaired fasting glucose, type 2 diabetes mellitus or diabetes mellitus, normal weight, and overweight in 13 studies [39,[42], [43], [44], [45], [46], [47], [48], [49], [50], [51], [52], [53]].