Gastrointestinal surgery and gut hormones

Abstract

Purpose of review Surgical treatment of obesity remains by far the most effective means of achieving weight loss, and in addition leads to normalised glucose tolerance in patients with type 2 diabetes mellitus (T2DM). Bariatric surgical procedures have recently been shown to effect changes in the secretion of gastro-intestinal hormones involved in energy regulation and intermediary metabolism that may contribute to appetite reduction, weight loss and remission of T2DM. Recent findingsGhrelin is released from the stomach in the pre-prandial state and stimulates food intake. Weight loss through dietary restraint elevates the low circulating levels of ghrelin in obese subjects, but following Roux-en-Y gastric bypass surgery (RYGB), obese subjects were shown to have suppressed levels of ghrelin. Subsequent prospective studies, however, have found inconsistent ghrelin responses following RYGB. Peptide YY (PYY) is expressed in the ileum, released in response to the ingestion of food and acts centrally to inhibit food intake. Recent studies have shown that PYY levels are reduced in obesity although obese subjects remain sensitive to exogenous PYY. Following RYGB, PYY release is exaggerated, an effect that should inhibit subsequent meal size. Glucagon-like peptide 1 (GLP-1), released from the same cells as PYY, shows a pronounced post-prandial elevation after RYGB that may be responsible for an enhanced early insulin release and contribute to the normalisation of glucose homeostasis. SummaryThe pleiotropic endocrine effects of RYGB that favor weight loss present strong circumstantial evidence for a humoral effect of RYGB on appetite and food intake. Mimicking the effects of RYGB on the entero-hypothalamic axis has become an attractive goal for pharmacotherapy.

Gut Hormone Profiles Following Bariatric Surgery Favor an Anorectic State, Facilitate Weight Loss, and Improve Metabolic Parameters

“…These studies have recently been reviewed, and the heterogeneity of the findings makes it unlikely that ghrelin has a major role in the weight loss after RYGB. 46 In our study, compared with lean control subjects, both bypass and banding patients had lower fasting ghrelin levels, although these were similar to those of the obese control subjects. In agreement with the majority of studies, we did not find an anticipated compensatory rise in ghrelin among surgical subjects.…”

A Rodent Model of Adjustable Gastric Band Surgery—Implications for the Understanding of Underlying Mechanisms

“…Roux-en-y gastric bypass surgery has been associated with marked changes in gut peptide levels. For example, the majority of studies have shown that the orexigenic hormone ghrelin which is secreted from the stomach and preempts initiation of meals is reduced in the blood following gastric bypass [12,13]. Conversely, peptides such as peptide YY (PYY) and glucagon-like peptide 1 (GLP-1), which normally reduce food intake as well as stimulate insulin release and inhibit glucagon secretion when given to obese subjects, are elevated postprandially following gastric bypass consistent not only with an effect on reduced appetite but also with an amelioration of non-insulin-dependent diabetes mellitus [14].…”

Effect of Different Bariatric Operations on Food Tolerance and Quality of Eating

“…The causes for reduced food tolerance may have different mechanisms. These bariatric operations can limit the consumption of specific types of foods that cannot be digested well (e.g., vegetables, red meat) [8], while some patients report a generalized satiety following bariatric operations [9][10][11][12].Those changes may be derived from distinct influences on the secretion of gastrointestinal peptides that are involved in the regulation of appetite and eating behavior [13,14]. The effect of purely restrictive procedures such as laparoscopic adjustable gastric banding (LAGB) or sleeve gastrectomy (SG), and malaborptive procedure such as biliopancreatic diversion with duodenal switch (BPD-DS) or other combined restrictive and malabsorptive procedures such as Roux-en-Y gastric bypass (RYGB), on weight loss, nutritional deficiencies, quality of life improvement, correction of co-morbidities, and complications has been well documented [2,3,15,16].…”