Gastric inhibitory polypeptide (GIP) and insulin in obesity: II. Reversal of increased response to stimulation by starvation of food restriction.

Abstract

The response of serum immunoreactive gastric inhibitory polypeptide (IR-GIP) and immunoreactive insulin (IRI) to a liquid mixed test meal, glucose or fat has been examined in obese subjects before and after starvation or reduced caloric intake (800 calories). Basal serum levels of IR-GIP increased significantly during starvation of obese persons and remained elevated over the whole starvation period while basal serum IRI levels decreased. The exaggerated IR-GIP response of obese subjects with normal or pathological glucose tolerance to a test meal and of obese subjects with glucose intolerance to 100 g glucose ingestion decreased significantly after starvation or food restriction. Simultaneously, the serum IRI response decreased. The exaggerated IR-GIP response of obese subjects to oral triglycerides which did not affect serum IRI or glucose levels was also significantly decreased after food restriction. The IR-GIP response of obese subjects to a test meal was already reduced after 5 days of food restriction together with an improved glucose tolerance. At this stage the IRI response was unchanged. After weight reduction in obese subjects there was a significant decrease of the IRI response to oral but not to intravenous glucose, while the glucose response decreased irrespectively of the mode of glucose administration. The IR-GIP response decreased only after oral glucose. The data are compatible with the hypothesis that the exaggerated IR-GIP response of obese subjects to oral glucose or fat load is secondary to the increased food intake and that changes in IRI response to oral glucose are related to changes in IR-GIP response.