New-found link between microbiota and obesity

Table 1 Prevalence of gut microbiota in health and disease

Microbiota in normal gut	Microbiota in obesity
Firmicutes phylum	Increase in Firmicutes phylum
Bacteriodetes phylum	Reduced abundance of Bacteroidetes
Actinobacteria phylum	A higher level of Actinobacteria phylum
Verrucomicrobia phylum	Lower proportion of Verrucomicrobia
Faecalibacterium prausnitzii species	Reduced abundance of Faecalibacterium prausnitzii species

Table 2 Microbiota having doubtful role in obesity

Microbiota
Archaea (a domain of microorganisms)
Phylum Firmicutes: Erysipelotrichi (a class of bacteria)
Methanobacteriales (an order of bacteria)
Prevotellaceae (a family of bacteria)
Ruminococcus (a genus of bacteria)
Bacteroides thetaiotaomicron and Methanobrevibacter smithii
Clostridium ramosum (a member of the Erysipelotrichi)
Clustridium leptum (cluster IV) (associated with both obesity and weight loss)
Specific species from Oscillibacter and Clostridium clusters XIVa and IV
Lactobacillus spp. - Lactobacillus reuteri

Table 3 Gross mechanisms involved in short-chain fatty acids-induced obesity

Butyrate

A major energy source for colonocytes

Involved in cellular apoptosis, proliferation and differentiation

Possesses metabolic effects like increase in mitochondrial activity, prevention of metabolic endotoxemia and activation of intestinal gluconeogenesis

Improves insulin sensitivity and increases energy expenditure by improving mitochondrial function resulting in reduction of obesity

Increases intestinal barrier function - an antiinflammatory potential

Protects against diet-induced obesity without causing hypophagia - the action being mediated through stimulation of anorexigenic gut hormones

Increases the expression of the gene coding for synthesis of leptin

Propionate

Increases the expression of the gene coding for synthesis of leptin

Protects against diet-induced obesity without causing hypophagia - the mechanism being similar to butyrate

Decreases cholesterol synthesis by inhibiting the activity of the enzyme acetyl-CoA synthetase

Acts as a precursor for hepatic gluconeogenesis thereby decreasing the hepatic synthesis of cholesterol

Inhibits the expression of resistin in human adipose tissue

Acetate

Acts as a substrate for lipogenesis and cholesterol synthesis in liver and other tissues

Gives protection against diet-induced obesity without causing hypophagia