Gastric inhibitory polypeptide (GIP) stimulated by fat ingestion in man

Ten normal volunteers ingested emulsified corn oil and the immunoreactive GIP, insulin (IRI) and nonesterified fatty acid (NEFA) responses were measured. Serum GIP levels increased after the ingestion of corn oil in all subjects, rising from a mean fasting level of 272 pg/ml to 856 +/- 272 pg/ml (P less than 0.05) by 30 minutes. The peak mean serum GIP concentration of 1,345 +/- 291 pg/ml occurred at 60 minutes; and mean serum GIP levels at 180 minutes remained significantly elevated over fasting values. Serum IRI, glucose and NEFA concentrations did not change during the 180 minutes of study. No changes in serum GIP concentrations occurred when, for control purposes, six volunteers ingested water on another day. We conclude: 1) Fat is a potent stimulus for the release of GIP in normal individuals. 2) Endogenously released GIP is not insulinotropic under the conditions of this study.