Glucagon like peptide-1 (GLP-1) dynamics following bariatric surgery: a Signpost to a new frontier

Glucagon like peptide-1 (GLP-1) is one of the gastrointestinal peptides implicated in glycaemic homeostasis. In non-obese individuals with normal glucose tolerance GLP-1 is secreted in response to nutrient intake. However, this GLP- 1 response is generally accepted to be significantly diminished in those with diabetes, obesity or both. Given that GLP-1 is secreted from enteroendocrine L cells in the intestine, it is not surprising that manipulation of the gastro- intestinal tract has been shown to alter GLP-1 secretion; particularly when this intestinal manipulation is designed to aid weight reduction. GLP-1 dynamics are altered by bariatric surgery, with an improved secretory response to nutrient intake. However, there remains debate on the mechanisms responsible for the alterations in GLP-1 dynamics. Here we review the evidence for GLP-1 dynamics after Roux-en-Y gastric bpyass (RYGB), adjustable gastric banding (AGB), biliopancreatic diversion (BPD) and sleeve gastrectomy (SG), and make comparisons between modalities. In addition, we review the potential mechanisms underlying these dynamics, other molecules that may add to the "incretin effect" and other possible roles for GLP-1 following bariatric surgery. Finally, we will offer our critique of the evidence base.