The Correlation and Intervention of Intestinal Flora and Frailty in the Elderly

100 healthy controls, 100 pre-frailty and 100 frailty elderly will be included. the healthy controls will be received no intervention. The pre-frailty will be randomized at a 1：1 ratio to receive prebiotics (inulin) or placebo (maltodextrin) . The degree of improvements and correlation in frailty will be evaluated three months later.Similarly,the frailty also will be randomized at a 1：1 ratio to receive prebiotics (inulin) or placebo (maltodextrin). The degree of improvements and correlation in frailty will be evaluated three months later.