OBJECTIVETo investigate the secretion patterns of glucose-dependent insulinotropic polypeptide (GIP) after different dietary loads in subjects with normal glucose tolerance (NGT) and their relation to insulin secretion and plasma glucose levels.

METHODSFourteen subjects with normal glucose tolerance underwent 75 g glucose tolerance test(OGTT) followed by mixed meal tolerance test(MMT) one week later. Blood glucose, insulin, and GIP were measured in the fasting state and at 0, 15, 30, 60, 90 and 120 min after glucose load or mixed meal load.

RESULTSThe first peak value of GIP after glucose load occurred at 15 min (45.09∓4.67 pmol/L). After a brief decline, GIP continued to increase till reaching 59.66∓11.73 pmol/L at 120 min after the load. After the mixed meal load, GIP secretion presented with two peaks: the first peak appeared at 15 min (71.69∓14.19 pmol/L) with a level significantly higher than that at 15 min following glucose load (P<0.05), and the second occurred at 90 min (55.35∓13.19 pmol/L). The area under curve of GIP showed no significant difference between the two loads (P>0.05). Compared with glucose load, mixed meal load resulted in an increase of the first GIP peak and an earlier insulin peak (30 min vs 60 min), but a significant decrease of blood glucose at 15 min (P<0.05).

CONCLUSIONCompared with glucose load, mixed meal (containing fat) can strongly stimulate GIP release and cause earlier occurrence of the insulin peak, which might be an important reason for the lower blood glucose after mixed meal.