**5. Conclusions**

Although various surgical methods may have long-term side effects, they can lead to the improvement of obesity and its related disorders, and changes in the microbiota and related metabolites are effective in this matter. For example, bacteria of the genus Klebsiella, which has increased after RYGB, by producing putrescine and metabolizing This polyamine into GABA can increase the GLP-1 levels and improve insulin resistance. Similarly, the genus Lachnobacterium, which increased after RYGB improves glucose homeostasis and insulin resistance via short-chain fatty acids. Species, such as pneumonia, Klebsiella, Alistipes, muciniphila, and Akkermansia, are species that are augmented after RYGB and their relative abundance is associated with reduced adiposity. Also, SG leads to persistent changes in the intestinal microbiome by decreasing dysbiosis due to an increase in Bacteroidetes and a decrease in Firmicutes. Changes in gut microbiota are less pronounced in LSG patients versus RYGB patients. Also, The positive outcomes of BPD/SD surgery may be because of gut microbiota modulation and more specifically increase in Bifidobacterium abundance throughout the gastrointestinal tract. In BPD/DS, unlike RYGB, it was shown that Bifidobacteriales elevated significantly as represented by the increasing abundance of the Bifidobacterium genus.
