Episode 6 - Why bariatric surgery improves metabolic parameters quickly
Episode 5 of the Break Nutrition Show Gabor and I had a discussion about the paper called “Mechanisms facilitating weight loss and resolution of type 2 diabetes following bariatric surgery”.
Mechanisms facilitating weight loss and resolution of type 2 diabetes following bariatric surgery
Bariatric surgery is more akin to metabolic surgery than a procedure to mechanically restricting food intake
The 3 classical categories of bariatric surgery (1) restrictive (2) malabsorptive (3) hybrid of 1 & 2
Improvement of metabolic parameters following Roux-en-Y Gastric Bypass (RYGB) surgery cannot be explained by malabsorption
RYGB patients are less hungry, consume fewer meals and eat less overall (particularly of energy dense foods)
How the anatomy is changed rather than by how many calories it mechanically restricts better explains differences in cure rates depending on the procedure: Gastric Banding ‘cures’ 48% of patients versus 84% for RYGB procedures
The Hindgut Hypothesis purports to explain favorable outcomes of bariatric surgery by suggesting that the procedure delivers more undigested food to the under-stimulated L-cells in the distal gut which results in an ‘opposite imbalance’, PYY and GLP-1 release is exaggerated, increasing the anorectic effect
Ileal Transposition studies are strong evidence for the Hindgut Hypothesis because total gut length remains the same but ileum sees more food, resulting in greater GLP-1 & PYY secretion, creating a strong anorectic effect.
The Foregut Exclusion Hypothesis purports to explain favorable outcomes of bariatric surgery by suggesting that the procedure cuts out an unknown anti-incretin molecule in the foregut that’s hyper-active in diabetics (type 2’s) and that removing this unknown factor improves glucose homeostasis.
A more likely explanation than the Foregut Exclusion hypothesis is that, rather an cutting out an unknown anti-incretin molecule, the anatomical change enhanced GLP-1 secretion which itself has an anti-incretin effect.
The Foregut Exclusion and Hindgut Hypotheses are not mutually exclusive and might both be correct. In fact, it is possible that both explanations are needed to explain the range of observations available.
Nevertheless, the authors of this review paper conclude that the success of bariatric surgery is best explained by “increased hindgut stimulation due to enhanced nutrient delivery and subsequent exaggerated release of hindgut hormones, such as GLP-1 and PYY”