Table 2.

Functional activities of normal gut flora

Protective function	Metabolic function	Structural function
Nutrient competition; Barrier fortification; Innate and adaptive immunity activation; Antimicrobial compounds secretion	Vitamin and amino acid biosynthesis; Bile acid biotransformation; Dietary fiber fermentation; Short chain fatty acids production	Mucus layer properties; Crypt and villi development; Villi microvascularization; Tight junction regulation

Seven division of bacteria (Firmicutes, Bacteroidetes, Proteobacteria, Fusobacteria, Verrucomicrobia, Actinobacteria, Cynobacteria), 300-1000 species.