Do Appetite-Suppressing Gut Peptides Explain Weight Loss After Sleeve Surgery? This Study Says No | Research

The takeaway

GLP-1 and PYY gut peptide responses appear to play a negligible role in weight loss after sleeve gastrectomy, suggesting other mechanisms drive surgical weight loss.

GLP-1 not stimulated
Meal consumption did not stimulate GLP-1 release in obese patients regardless of whether it was before or after sleeve gastrectomy surgery

What the researchers found

Contrary to expectations, the appetite-suppressing gut peptides GLP-1 and PYY do not appear to be major drivers of weight loss after sleeve gastrectomy. In 10 obese patients studied before and 3 months after surgery, GLP-1 release after meals was not stimulated regardless of eating speed or surgical status. PYY levels did increase after surgery (higher post-op than pre-op), but the speed of eating made no difference.

Interestingly, fast eating produced greater satiety than slow eating in both pre- and post-operative states, contradicting common dietary advice. Hunger and satiety responses to food were similar before and after surgery. Sleeve gastrectomy did improve insulin resistance regardless of eating speed. The authors conclude that anorexigenic gut peptide responses play a "negligible" role in sleeve gastrectomy-induced weight loss, suggesting other mechanisms (mechanical restriction, altered ghrelin, neural signaling) are more important.

Why it matters

A leading theory for why bariatric surgery causes weight loss is that it changes gut peptide secretion — boosting appetite-suppressing peptides like GLP-1 and PYY. This study challenges that theory for sleeve gastrectomy specifically, finding that GLP-1 wasn't stimulated at all and PYY changes were modest. Understanding which mechanisms actually drive surgical weight loss is critical for developing peptide-based alternatives to surgery.

The numbers in context

n=10 · Pre- and post-LSG (3 months) · GLP-1 not stimulated by meals in either state · PYY increased post-op vs. pre-op · Fast feeding = higher satiety than slow · Insulin resistance improved post-surgery

How the study worked

Prospective clinical study in 10 obese patients undergoing laparoscopic sleeve gastrectomy. Patients were tested before and 3 months after surgery with fast and slow meal challenges. Circulating GLP-1, PYY, glucose, insulin, and triglycerides were measured at multiple timepoints. Visual analogue scales assessed hunger and satiety. Responses were compared across feeding speeds and surgical states.

Who was studied

Obese patients undergoing laparoscopic sleeve gastrectomy

What this study cannot tell us

Very small sample size of only 10 patients severely limits statistical power and generalizability. Three months post-surgery may be too early to capture long-term changes in gut peptide secretion. The study only measured GLP-1 and PYY, missing other gut peptides like CCK, oxyntomodulin, and ghrelin that may be more relevant. No non-obese control group for comparison.

How to read the evidence

This is a small prospective clinical study with only 10 participants, which severely limits the strength of conclusions. The repeated-measures design (same patients before and after surgery) adds some rigor, but the findings should be considered preliminary and hypothesis-generating.

When this study was published

Published in 2017. The findings remain relevant to the ongoing debate about mechanisms of bariatric surgery-induced weight loss, though larger studies have since added nuance to the gut peptide picture.

The bigger picture

The success of GLP-1 drugs like semaglutide for weight loss was inspired partly by the observation that bariatric surgery changes gut peptide secretion. This study complicates that narrative for sleeve gastrectomy, suggesting the surgery's weight loss benefits come from other mechanisms — perhaps reduced stomach volume, altered ghrelin signaling, or changes in vagal nerve communication. Understanding these differences helps explain why peptide drugs and surgery may work through partly different pathways.

Questions still open

If GLP-1 release doesn't increase after sleeve gastrectomy, why do GLP-1 drugs produce similar weight loss to surgery?
Would longer follow-up (12+ months) reveal delayed changes in gut peptide secretion after sleeve gastrectomy?
Do other bariatric procedures like Roux-en-Y bypass show different GLP-1 and PYY responses than sleeve gastrectomy?

Common questions

Does sleeve gastrectomy increase GLP-1 levels?

This study found it does not — GLP-1 release was not stimulated by meals either before or after sleeve gastrectomy. This is different from Roux-en-Y gastric bypass, which has been shown to dramatically increase GLP-1 secretion. The finding suggests sleeve gastrectomy works through other mechanisms like stomach restriction and ghrelin reduction.

Does eating speed matter for gut peptide release after bariatric surgery?

In this study, eating speed (fast vs. slow) did not significantly affect GLP-1 or PYY release in either surgical condition. Interestingly, fast eating actually produced greater feelings of fullness than slow eating, contradicting the common advice to eat slowly for better satiety.

Read the original research

Post-prandial anorexigenic gut peptide, appetite and glucometabolic responses at different eating rates in obese patients undergoing laparoscopic sleeve gastrectomy.

Endocrine, 55(1), 113-123

View on PubMed ↗Publisher’s paper ↗

Citation

Rigamonti, Antonello Emilio; Bini, Silvia; Rocco, Maria Cristina; Giardini, Vittorio; Massimini, Diego; Crippa, Maria Grazia; Saluzzi, Antonella; Casati, Marco; Marazzi, Nicoletta; Perotti, Mario; Cimino, Vincenzo; Grassi, Guido; Sartorio, Alessandro; Pincelli, Angela Ida. (2017). Post-prandial anorexigenic gut peptide, appetite and glucometabolic responses at different eating rates in obese patients undergoing laparoscopic sleeve gastrectomy.. Endocrine, 55(1), 113-123. https://doi.org/10.1007/s12020-016-0933-6