After sleeve gastrectomy, patients with high insulin resistance showed greater gut microbiome shifts (more Akkermansia, less Prevotella) and enhanced GLP-1 and GLP-2 incretin responses, with 26.5% total weight loss at 6 months.
26.5% weight lossBoth groups lost over a quarter of body weight at 6 months, with enhanced GLP-1 and GLP-2 responses — but gut bacteria changes were most dramatic in the insulin-resistant group
What the researchers found
At 6 months post-sleeve gastrectomy, mean total weight loss was 26.5 ± 6% across both groups. Both high-IR and low-IR patients showed enhanced GLP-1 and GLP-2 secretion in response to meal tolerance testing after surgery.
At baseline, the high-IR group had higher relative abundance of Prevotella species (associated with adverse metabolic and inflammatory profiles). After surgery, the high-IR group experienced more pronounced microbiome changes: increases in Akkermansia and Veillonella species and decreases in Prevotella. Enhanced GLP-1 and GLP-2 responses correlated with weight loss and metabolic improvement, with this correlation being particularly strong in the low-IR group. These findings suggest insulin resistance status at baseline shapes both the microbiome remodeling and incretin peptide responses to surgery.
Why it matters
This study reveals that the metabolic benefits of bariatric surgery depend partly on how the gut microbiome and incretin peptide systems respond — and that response differs based on pre-existing insulin resistance. Understanding this interaction could help predict who will respond best to surgery and identify patients who might benefit from microbiome-targeted interventions (like probiotics or prebiotics) alongside surgery to optimize outcomes.
How the study worked
This was a prospective single-center study of 18 patients with severe obesity (mean BMI 45.03) and normal glucose tolerance who underwent sleeve gastrectomy. Patients were stratified by HOMA-IR index into high-IR (>95th percentile, n=9) and low-IR (<25th percentile, n=9) groups. Body composition, biochemistry, and gut microbiota were assessed before and 6 months after surgery. GLP-1 and GLP-2 responses were measured using a standardized meal tolerance test at both time points.
What this study cannot tell us
The study had a very small sample size (9 per group), limiting statistical power and generalizability. Only sleeve gastrectomy was studied — results may differ with gastric bypass or other procedures. The 6-month follow-up may not capture long-term microbiome and incretin changes. All patients had normal glucose tolerance, so findings may not apply to those with diabetes. The correlation between GLP-1 responses and weight loss was stronger in the low-IR group, which needs explanation in larger studies.
How to read the evidence
This is a small prospective human study (n=18) with careful stratification and both microbiome and incretin peptide measurements. While the mechanistic detail is valuable, the very small sample size limits the reliability and generalizability of the findings.
When this study was published
Published in 2026, this is a cutting-edge study at the intersection of microbiome science, incretin biology, and bariatric surgery — three rapidly advancing fields.
The bigger picture
The gut microbiome-incretin axis is emerging as a central mechanism behind why bariatric surgery works. GLP-1 and GLP-2 are incretin peptides produced by gut cells that regulate appetite, blood sugar, and intestinal health. This study connects three hot topics in metabolic research — the microbiome, incretin peptides, and insulin resistance — showing they form an interconnected system that surgery reshapes. As GLP-1 drugs become widely used for obesity, understanding how the natural GLP-1 response changes after surgery adds important context for when to combine pharmacological and surgical approaches.
Questions still open
- Could probiotic supplementation with Akkermansia before or after bariatric surgery enhance the incretin and weight loss response?
- Why did GLP-1 responses correlate more strongly with weight loss in the low-IR group — does high insulin resistance blunt the GLP-1 benefit?
- Would patients with high insulin resistance benefit from combining GLP-1 drugs with bariatric surgery to maximize outcomes?
Common questions
What are GLP-1 and GLP-2, and why do they increase after bariatric surgery?
Why does the gut microbiome matter for weight loss surgery?
Read the original research
Insulin resistance modulates gut microbiota and incretin response remodeling after bariatric surgery in severe obesity.
International journal of obesity (2005), 50(3), 568-578
Citation
Puig, Rocío; Rodríguez-Peña, M-Mar; Hernández-Montoliu, Laura; Astiarraga, Brenno; Martínez, Eva; Balibrea, Jose M; Llauradó, Gemma; Tarascó, Jordi; Caballero, Albert; Joaquín, Clara; Puig-Domingo, Manel; Vilarrasa, Nuria; Fernández-Veledo, Sonia; Vendrell, Joan; Pellitero, Silvia. (2026). Insulin resistance modulates gut microbiota and incretin response remodeling after bariatric surgery in severe obesity.. International journal of obesity (2005), 50(3), 568-578. https://doi.org/10.1038/s41366-025-01971-7