Secretion and Function of Gastrointestinal Hormones after Bariatric Surgery: Their Role in Type 2 Diabetes

Bariatric surgical procedures were designed primarily to promote weight loss in morbidly obese individuals. There is increasing evidence that, apart from producing durable weight loss, bariatric surgery powerfully ameliorates type 2 diabetes in the majority of morbidly obese individuals. Its role is also being investigated in less obese patients, with generally favourable short-term results. While massive weight loss undoubtedly plays an important role in consolidating the long-term anti-diabetic impact of bariatric surgery, the role of the altered hormonal gut milieu is now known to be integral to improved glucose homeostasis. Changes in levels of glucagon-like peptide 1 (GLP-1), gastric inhibitory peptide, peptide YY (PYY) and ghrelin have been described following metabolic surgery. The various surgical procedures differ in their respective abilities to modulate gut hormones, depending on whether they involve intestinal diversion or are purely restrictive. The postprandial GLP-1 response to an oral glucose tolerance test or mixed test meal is augmented following gastric bypass surgery or biliopancreatic diversion, while no change is observed after gastric banding. Increased PYY levels have been reported following gastric bypass. Levels of ghrelin, an orexigenic hormone, do not rise following weight loss due to gastric bypass, although this is not reported consistently in all studies. In this paper, the authors review the current evidence regarding the use of metabolic surgery to treat type 2 diabetes, focusing on published data from animal and human studies regarding gut hormone secretion and function following bariatric surgery.