Bariatric Gastric Bypass Surgery Alters Gut Microbiome Among Adults With Type 2 Diabetes and Mild Obesity

Gastric bypass surgery.
Gastric bypass surgery.
Researchers assessed how gut microbiota changes are associated with anthropometric, metabolic, and inflammatory profiles following metabolic surgery in adults with type 2 diabetes and mild obesity.

This study of adults with type 2 diabetes with class 1 obesity examined gut microbiota changes after metabolic Roux-en-Y gastric bypass (RYGB) bariatric surgery vs standard medical therapy. For patients receiving RYGB, the overall microbial ecosystem changed significantly during the follow-up period, and improvements in anthropometric, metabolic, and inflammatory biomarkers were strongly associated with an increase in microbial richness and Proteobacterial lineages. A continuous increase in genus richness was seen after RYGB up until month 12; patients receiving standard medical therapy had significantly lower genus richness at the same endpoint. The results of this study were reported in Diabetology and Metabolic Syndrome.

The randomized controlled trial of 20 patients was conducted in Portugal. Ten patients were randomly assigned to undergo surgery and 10 to receive standard medical care.

Antidiabetic standard medical therapy included nutrition and exercise counseling, frequent glucose self-monitoring and titration strategies, and drug therapy for hyperglycemia and restoration of pancreatic cell function, as well as lipid and blood pressure control. All participants receiving standard antidiabetic medical therapy failed to achieve diabetic remission, whereas 62.5% of the bariatric gastric bypass surgical group did.

Anthropometric measurements and laboratory tests were performed 6 times: at screening; at baseline after randomization; and at months 1, 3, 6, and 12 after surgery or the first consultation in the medical group. Anthropometric measurements included body weight, height, waist circumference, visceral fat area, body fat mass, and lean muscle mass using bioimpedance analysis.

Laboratory tests included blood biochemical tests after 8 hours of fasting at each visit. Glucose, fasting glucose, total cholesterol, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), triglycerides, hemoglobin A1c, insulin, C-reactive protein, and C-peptide values were determined. A gut microbiota analysis was performed following sterile stool collection.

At each follow-up, the surgical group made consistent progress compared with the medical group. At the 1-year follow-up, body mass index (BMI) in the surgical group was 24.6 kg/m2 vs 30.5 kg/m2 in the medical group. Weight loss was 25.5% in the surgical group vs 4.9% in the medical group. Waist circumference, visceral fat, body fat mass, insulin, fasting glucose, and C-peptide levels were all significantly lower and HDL-C was higher in the surgical group.

The surgical group demonstrated a continuous increase in genus richness at each follow-up visit (61±9 prokaryotic genera at baseline to 76±9 prokaryotic genera at month 12), whereas the medical arm showed no change (71±11 at baseline to 71±10 at month 12). The surgical group had a decrease in Firmicutes phyla, which have anti-inflammatory properties benefiting metabolic health. Lower Firmicutes phyla numbers indicate decreased inflammation.

The surgical group showed an increase in Proteobacteria. This increase might be due to decreased stomach acid secretions after stomach size reduction. Higher pH facilitates bacterial colonization. Proteobacteria are facultative anaerobes, and their presence increases oxygen availability, thus affecting metabolic health characteristics.

Caloric restriction following bariatric surgery also leads to higher amounts of undigested nutrients, which may affect the nutrient availability for specific bacterial species.

Limitations of this study include the small sample size, the complexity of the different technical aspects of microbiome analysis, and the uncontrolled variables such as the various dietary profiles and levels of physical activity that factor into the phenotypic outcomes.

There is a strong inverse relationship between changes in body composition and anthropometric, inflammatory, and metabolic markers along with changes in microbial richness following bariatric surgery. Because standard medical therapy for obesity does not improve gut microbiota, using prebiotics and probiotics may be an alternative treatment strategy for those who decline bariatric surgery.

Future research should explore other variables such as diet, hormonal fluctuations, bile acid metabolism, and physical activity post-RYGB to explain the metabolic improvement seen in patients with type 2 diabetes and mild obesity.


Lau E, Belda E, Picq P, et al. Gut microbiota changes after metabolic surgery in adult diabetes patients with mild obesity: a randomised controlled trial. Diabetol Metab Syndr. 2021;13(1):56. doi:10.1186/s13098-021-00672-1

This article originally appeared on Endocrinology Advisor