Severe obesity and bariatric surgery: what is the impact on the intestinal microbiota?


For the first time, French researchers have characterized the intestinal microbiota and the metabolic signatures of severely obese patients, as well as the changes observed following two types of bariatric surgery. These patients could benefit from more targeted actions to correct the severity of their dysbiosis before or after surgery.


It is known that gut bacterial gene richness tends to diminish in moderately obese patients. A French team studied the impact of two types of bariatric surgery on this genetic depletion for 1 year in severely and morbidly obese patients (BMI >35 kg/m2): on the one hand, gastric banding which reduces the volume of the stomach (therefore the quantity of food ingested, that is the equivalent of a conventional reduction in caloric intake); on the other hand, the Roux-en-Y gastric bypass, which combines a reduction in the size of the stomach pouch and bypassing part of the small intestine and the stomach to reduce absorption of food.

Specific bacterial signature

First finding: 75% of the severely obese women recruited displayed reduced gut microbial gene richness, versus 20 to 40 % in moderately obese individuals. This reduction was also associated with more marked metabolic complications (insulin resistance, visceral fat, adipocyte size, inflammatory markers…) and with a specific bacterial signature. Gut microbial gene richness is therefore thought to be an indicator of the severity of obesity and of associated intestinal inflammation.

Gastric bypass gave better results

One year after surgery (banding or bypass), the gut bacterial gene richness of these patients was increased, although this recovery was partial in all participants. A greater improvement in body composition, as well as in metabolic profiles (particularly the cluster of metabolites comprised of glycine, acetyl glycine and methylmalonate) and inflammatory profiles was also observed in the bypass patients.

Insufficient increase in gene richness

However, it may be difficult to explain these metabolic improvements by the sole fact of increased gut microbial gene richness: the post-surgical increase in gene richness reached a peak one year after the procedure but did not show any subsequent additional progression. On the other hand, the link between a low level of gut gene richness (as a cause or consequence of obesity), and the duration of the disease remains to be clarified. Nevertheless, the authors suggest that the dysbiosis be corrected before or after the bariatric procedure by means of specific diets, the use or pre- or probiotics or fecal microbiota transplant. Objective: to bring about a sustained improvement in the metabolic health of severely obese patients.



J Aron-Wisnewsky et al. Major microbiota dysbiosis in severe obesity: fate after bariatric surgery. Gut Microbiota. June 2018