How Does Bariatric Surgery Work?

sharma-obesity-gastric_bypass_roux-en-y3Regular readers will be well aware of the fact that bariatric (unfortunately, often referred to as “weight-loss surgery”) is currently the most effective treatment for severe obesity.

However, exactly why and how surgery works remains unclear. Earlier concepts of surgery working either because it creates a mechanical restriction to food intake and/or reduces caloric load due to malabsorption are not borne out by newer studies.

Rather, it seems that complex neurohormonal changes together with often profound changes in ingestive behaviour act together to account for the resulting weight loss (and more importantly) for the long-term weight-loss maintenance.

Just how many factors interact in specific and unspecific ways to lower body weight is now discussed in a review paper by Timothy Sweeney and John Morton, from Stanford University, in a paper published in Clinical Gastroenterology.

As the authors discuss, there is a complex interaction between a wide range of factors including several hormones (leptin, ghrelin, adiponectin, glucagon-like peptide 1 (GLP-1), peptide YY, and glucagon), bile acid changes in the gut and the serum, and changes to the gut microbiome.

The most profound changes in these systems are seen with the roux-en-Y gastric bypass, which induces large and distinctive changes in most measured fat and gut hormones, including early and sustained increase in GLP-1, possible through intestinal bile acid signaling. This may well explain why this operation appears to be the most effective and durable procedure.

Clearly, hope remains that by better understanding the exact mechanisms through which surgery (which will only ever be available to a vanishingly small minority of people with excess weight) works, we will identify mechanisms and targets for desperately needed pharmacological treatments.

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