Figure 4.

 Racial differences in secretion and metabolism of (a) glucose‐dependent insulinotropic polypepide (GIP) and (b) glucagon‐like peptide (GLP)‐1. GIP secretion in healthy Japanese subjects after ingestion of glucose or mixed meals were higher than those of healthy Caucasian subjects, whereas levels of intact GIP were similar^37,40–42. This suggests processing of GIP by dipeptidyl peptidase‐4 (DPP‐4) in Japanese subjects might be enhanced. Considerably low levels of intact GLP‐1 after ingestion of glucose or mixed meals are also consistent with enhanced DPP‐4 activities in Japanese subjects. To compare early phase incretin secretion and their processing by DPP‐4 between non‐obese (BMI <25) healthy Japanese and Caucasian subjects, area under the curves during 0–30 min after ingestion of mixed meals containing similar calories are plotted for total and intact forms of (a) GIP and (b) GLP‐1 from Yabe et al.⁴² Note that total and intact GIP and total GLP‐1 levels were measured in the same immunoassays, whereas assays for intact GLP‐1 were similar except for the presence or absence of the ethanol extraction.