Objective Human gastrointestinal tract is colonized by thousands of microbial species,closely associated with host nutrition,metabolism and immunity.Selective modulation of gut microbiota with antibiotics,probiotics and prebiotics had been proposed to be a novel therapeutic strategy to improve host health.Prebiotics were defined as "non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon,and thus improves host health".