Gut microbiome: Linking together obesity, bariatric surgery and associated clinical outcomes under a single focus

Table 1 Comparison of the two main bariatric surgery procedures

	Roux-en-Y gastric bypass	Vertical sleeve gastrectomy
Technique	(1) 15-30 mL gastric pouch; (2) Gastrojejunostomy (GJ); (3) Jejunojejunal anastomosis (Roux-en-Y); (4) 30-50 cm distal to the ligament of Treitz; and (5) Remnant disconnected but left in situ	(1) Excision of lateral 70%-80% of stomach along the greater curvature; and (3) Approximately 100 mL gastric reservoir (sleeve)
Mechanism of action	(1) Instantaneous food transfer to small intestine, altering: Gut hormones; Bile acids; Neural signaling; Gut microbiota; Gut-brain-endocrine; Adipocyte-brain axes; and (2) Results in reduced food intake, increased satiety and altered food preferences	(1) Alterations in: Gut hormones; Bile acids; Neural signaling; Gut microbiota; Gut-brain-endocrine; Adipocyte-brain axes; and (2) Results in reduced food intake, hunger, increased satiety and altered food preferences
Advantages	(1) Significant long-term weight loss; (2) Glycemic control improvement in 90% of cases; (3) Maintain percent EWL in the long term; (4) Hunger reduction and satiety; (5) Food preferences changes; and (6) Increases energy expenditure	(1) Significant long-term weight loss (approximately 10% less than RYGB); (2) Glycemic control as effective as RYBG; (3) Maintain percent EWL in the long-term; (4) Hunger reduction and satiety; (5) Food preferences changes; (6) No anatomical rerouting of food; (7) Short length of stay (< 2 d); (8) Technically simpler than RYGB; and (9) Lower complication rate than RYGB
Disadvantages	(1) Technically complex (two anastomoses) compared with AGB or VSG; (2) Higher complication rate than AGB or LSG; for example, anastomotic leak or dumping syndrome can occur; (3) Longer length of stay; (4) Long- term vitamin and/or mineral deficiencies (for example, vitamin B12, iron, calcium or folate); (5) Requires lifelong vitamin and/or mineral supplementation; (6) Lifelong dietary changes; (7) Increases alcohol addiction and suicide rates; and (8) postprandial hypoglycemia	(1) Anastomotic leak can be difficult to manage; (2) Susceptible to long-term vitamin and/or mineral deficiencies (less common than with RYGB); (3) Precautionary lifelong vitamin and/or mineral supplementation; (4) Lifelong dietary changes; (5) Irreversible; and (6) potential risk of Barrett esophagus

EWL: excess weight loss; RYGB: Roux-en-Y gastric bypass.

Table 2 Changes in human gut microbiota following bariatric surgery

↑/↓	RYGB	VSG
↑	Akkermansia (Verrucomicrobia)	Bulleidia (Firmicutes)
↑	Escherichia (Protobacteria)	Roseburia intestinalis (Firmicutes)
↑	Klebsiella (Protobacteria)	Faecalibacterium prausnitzii (Firmicutes)
↓	Lactobacillus (Firmicutes)	Coprococcus comes (Firmicutes)
↓	Bifidobacterium (Actinobacteria)
↓	Faecalibacterium prausnitzii (Firmicutes)
↓	Coprococcus comes (Firmicutes)

RYGB: Roux-en-Y gastric bypass; VSG: Vertical sleeve gastrectomy.

Table 3 Literature findings on the postoperative changes of gut microbiota

Ref.	Postoperative GM changes
	Increased abundance	Decreased abundance	Comments
Graessler et al[71], 2013	Enterobacter, Citrobacter, Neurospora, Veillonella, Salmonella, Shigella, E. coli tended to increase	Faecalibacterium, Coprococcus, Helicobacter, Dictyostelium, Epidinium, Anaerostipes, Nakamurella, Methanospirillum, Thermomicrobium	-
Kong et al[68], 2013	Bacteroides, Alistipes, Escherichia	Firmicutes (Lactobacillus, Dorea, Blautia) Bifidobacterium	Increased richness of GM after RYGB
Palleja et al[50], 2016	Escherichia coli, Klebsiella pneumoniae, 10 species belonging to the genus Streptococcus, 4 from Veillonella, 2 from Alistipes, Bifidobacterium dentium, Enterococcus faecalis, F. nucleatum, and Akkermansia muciniphila	E. prausnitzii	-
Tremaroli et al[64], 2015	Gammaproteobacteria; Several Proteobacteria (Escherichia, Klebsiella, Pseudomonas); E. coli tended to increase but was not statistically significant	3 species of Firmicutes; (Clostridium difficile, Clostridium hiranonis, Gemella sanguinis)	-

GM: Gut microbiota; RYGB: Roux-en-Y gastric bypass.