The postprandial response of gastric inhibitory polypeptide to various dietary fats in man.

Gastric Inhibitory Polypeptide (GIP) is secreted in response to oral glucose, amino acid, and fats. In the presence of hyperglycemia, GIP augments nutrient stimulated insulin secretion. Studies looking at the effect of fat on GIP release, however, have focused primarily on corn oil, a polyunsaturated fat. To determine if other fats give similar GIP results to those with corn oil, nine normal subjects underwent four tolerance tests with fats derived from saturated (cocoa butter), monounsaturated (olive oil), or polyunsaturated (corn oil and fish oil) sources. Fifty grams of each triglyceride rich fat were ingested and serum cholesterol, triglyceride, glucose, insulin, and GIP levels were determined over a 180-minute period. Serum cholesterol, triglyceride, glucose, and insulin levels were similar following each fat tolerance test. GIP concentrations, however, were significantly lower (P less than 0.01) with the fish oil, when compared to the other fats studied. Similar GIP responses were observed with olive oil and corn oil, but both were higher than with the cocoa butter. These findings suggest that the source of fatty acids affect GIP secretion. The reason for these differences in serum GIP responses is uncertain, but is not readily explained by changes in serum glucose, insulin, or triglyceride concentrations. Since GIP augments nutrient stimulated insulin release 1-3 hours postprandially, the source of dietary fat consumed as part of a mixed meal could ultimately influence pancreatic beta cell insulin secretion.