Impact of bariatric surgery on gut microbiota

By short-circuiting the stomach or removing part of it, bariatric surgery significantly alters the gut microbiota. However, results seem to depend on the technique used.

Created 13 October 2020
Updated 31 March 2022

About this article

Created 13 October 2020
Updated 31 March 2022

Global prevalence of obesity almost tripled between 1975 and 2016 and now represents a major public health issue. Bariatric surgery is currently the best strategy for achieving lasting weight loss in patients suffering from morbid obesity1, with a five-year success rate of over 66%. It mainly consists of two techniques of comparable effectiveness: gastric bypass (or more precisely, laparoscopic Roux-en-Y gastric bypass) and sleeve gastrectomy, which involves removing two-thirds of the stomach. How do these interventions affect the bacterial ecosystem? Do the two approaches have the same impact?

Enriched and diversified intestinal microbiota

To find out, researchers compared two groups of around 100 patients, one subjected to gastric bypass and the other to sleeve gastrectomy. Six months later they observed a significant increase in bacterial abundance and diversity in the gut microbiota of all participants. 40% of bacteria were common to both approaches, including Akkermansia muciniphila–known to be negatively correlated with obesity–, as well as certain proteobacteria such as Escherichia coli, suspected of influencing both appetite and metabolism after surgery. However, only the gastric bypass caused a depletion of Faecalibacterium prausnitzii, a species associated with certain metabolic disorders and inflammatory bowel diseases.

Gastric bypass has a greatest impact

Both approaches also resulted in increased transport systems for vitamins B12 and B1, manganese, iron, and zinc, suggesting increased use of these nutrients by bacteria. According to the authors, the impact of gastric bypass was greater than that of sleeve gastrectomy in all aspects. However, they consider that a further three to five years will be required to establish whether these discoveries have the clinical ability to preferentially direct patients towards one treatment or the other.

1. Morbid obesity is defined by a body mass index (BMI) of over 40

Old sources


Farin W, Oñate FP, Plassais J, et al. Impact of laparoscopic Roux-en-Y gastric bypass and sleeve gastrectomy on gut microbiota: a metagenomic comparative analysis [published online ahead of print, 2020 Mar 20]. Surg Obes Relat Dis. 2020;S1550-7289(20)30132-5. doi:10.1016/j.soard.2020.03.014

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