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.