Gut microbiota in obesity

Table 1 Association between gut microbiomes and obesity

Microbiota characteristics in obesity	Preclinical or clinical	Study subjects	Ref.
Firmicutes/Bacteroidetes ratio increased	Preclinical	Mice	Ley et al[20], Turnbaugh et al[21]
	Clinical	Childhood	Indiani et al[22]
	Clinical	Adult ukrainian population	Koliada et al[23]
The relative abundance of Christensenellaceae was inversely related to host BMI	Clinical	Human	Waters et al[26]
	Clinical	Postmenopausal women	Alemán et al[33]
	Clinical	Italian elderly	Tavella et al[36]
Increased Akkermansia population reduced body weight	Clinical	Human	Depommier et al[27]
	Preclinical	Mice	Anhê et al[34]
Lactobacillus paracasei decreased, while Lactobacillus reuteri and Lactobacillus gasseri increased	Clinical	Human	Crovesy et al[28], Million et al[31]
Bifidobacteria reduced	Preclinical	Rats	Waldram et al[30]
Methanobacteriales smithii and Bifidobacterium were associated with normal weight	Clinical	Human	Million et al[31]

BMI: Body mass index.

Table 2 Mechanism of obesity induced by gut microbiota

Effect	Microbiota characteristics	Mechanism	Ref.
Increased energy absorption	Expansion of Desulfovibrio and loss of Clostridia	Elevated the expression of genes that control lipid absorption such as CD36	Petersen et al[44]
Extra energy for the host	The inverse association between fecal SCFAs and gut microbiota diversity; Faecalibacterium prausnitzii, Roseburia faecis, and other Clostridiales increased; Akkermansia muciniphila, Alistipes finegoldii, Bacteroides, Christensenellaceae, Methanobrevibacter, and Oscillospira decreased	Excessive SCFAs	de la Cuesta-Zuluaga et al[49]
Increased appetite	A community dominated by members of the Clostridial clusters XIVa and IV	The levels of peptide YY and GLP-1 in obese patients decrease significantly	Wu et al[54], Salehi et al[55], Federico et al[56]
Decreased Fat storage	Germ free mice colonized with Lactobacillus paracasei	Increase the expression of ANGPTL4, and inhibit LPL, leading to decreased fat storage	Aronsson et al[59], Tazi et al[60]
Increased fat storage	Transplanting gut microbes from conventionally raised mice into germ-free mice	Increasing the expression of ChREBP and SREBP-1, Fiaf is inhibited, activate LPL, help triglycerides enter the circulatory system from the liver	Bäckhed et al[19]
Decreased chronic inflammation	Increase levels in the butyrate-producing bacteria such as Ruminococcaceae and Lachnospiraceae	Inhibit pathways leading to the production of pro-inflammatory cytokines; Stimulate adipoliolysis and mitochondrial oxidative phosphorylation, thereby achieving greater energy consumption; Reduce LPS, thereby reducing chronic low-grade inflammation	Kang et al[66], Lührs et al[67], Jia et al[68]
Interruption of circadian rhythm	Bile salts biotransformation bacteria such as Lachnospiraceae, Clostridiaceae, Ruminococcaceae, Lactobacillus, Bacteroides, and Bifidobacterium	Regulate transcription of key genes involved in circadian rhythm (Dbp, Per1/2) and lipid metabolism (Pparγ, Angptl4)	Joyce et al[77], Parkar et al[78]

SCFAs: Short-chain fatty acids; LPL: Lipoprotein lipase; LPS: Lipopolysaccharide.