Bariatric surgery (BS) appears as a solution for managing cardiovascular risk in people with a severe and morbid Body Mass Index (BMI > 35-40 kg/m2). Although previous research has shown that the gut microbiota profile in obesity is characterized by low microbial gene richness and is correlated with some metabolic and inflammatory markers, little is known about its contribution to mediating the impact of BS on severe obesity.
A new cross-sectional study, led by Dr. Francisco Jose Tinahones from the University of Malaga and the Spanish Biomedical Research Centre in Physiopathology of Obesity and Nutrition (CIBERobn) (Spain), has found that interactions between the gut microbiota and bile acids metabolism may partially mediate the success of bariatric surgery in the medium term.
The researchers sought to explore the contribution of gut microbiome to the successful rates of BS in a prospective cohort of 24 patients who underwent Roux-en-Y gastric bypass (RYGB).
Based on excess weight loss follow-up from prior to gastric bypass to 60 months post-surgery, subjects were categorized as:
- Success (n = 6): excess weight loss equal to or higher than 50% at nadir weight and throughout follow-up.
- Primary failure (n = 6): excess weight loss less than 50% from the lowest weight achieved after gastric bypass until 60 months post-surgery.
- Weight regain (n = 12): excess weight loss higher than 50% at the lowest recorded weight postsurgical but excess weight loss less than 50% at the last follow-up visit.
The patients achieving excess weight loss of less than 50% from nadir weight post-surgery through follow-up (primary failure group) showed the worst BMI, weight, waist circumference, total cholesterol and LDL-cholesterol. In contrast, success and weight regain patients did not differ.
No differences in alfa diversity (richness and diversity) were reported in the gut microbiota between study groups.
With regard to specific gut microbiota profiles, some genera showed statistically significant differences among the study groups. They were Sarcina, Alkaliphilus, Pseudoalteromonas, Cetobacterium and the minor genera 5-7N15 and AF12. Patients belonging to the success group showed the highest abundance of these gut bacteria.
When comparing operational taxonomic units shared among all samples, the authors showed specific core gut microbiome profiles, with patients from the success group showing the most diverse gut microbiome, with 16 different taxa compared with the other groups.
The authors also predicted the gut microbiome’s potential function based on 16S ribosomal ribonucleic acid sequences. Although all gut microbiome samples from the different groups shared similar gut microbiome potentiality, the success groups showed a higher expression of the salt hydrolase gene involved in gastrointestinal bile acid deconjugation, with parallel alterations in lipid and cholesterol metabolism. Changes in this gene were attributed to Firmicutes, Bacteroidetes and Proteobacteria.
To further explore the functional implications of these findings, researchers performed correlations between gut microbiota changes and clinical parameters. The Sarcina genus was related to BMI and bacterial salt hydrolase activity and, in a predictive model, was also the best genera related to BMI post-surgery.
This investigation has run in parallel with another recent study that looked into the impact of different bariatric surgeries on severe obesity at several time points up to 12 months (with confirmed changes in the gut microbiome up to five years after BS in one cohort). Altogether, these findings might contribute to explaining the high variability levels in BS success rates in the long term. Further studies considering lifestyle factors that affect gut microbiome variability using bigger samples will help clinicians and scientists elucidate whether gut microbiota signatures are a cause or a consequence of severe obesity.
Gutiérrez-Repiso C, Moreno-Indias I, de Hollanda A, et al. Gut microbiota specific signatures are related to the successful rate of bariatric surgery. Am J Transl Res. 2019; 11(2):942-52. http://www.ajtr.org/files/ajtr0085422.pdf Published online 2019 Feb 15. Accessed 2019 Apr 4.