2.2. Study designThis study was a single center, randomized, double-blind, placebo-controlled, prospective trial with a 12-week probiotics intervention. Any changes in medication, health status or adverse events were recorded. All probiotic products except the test drink were forbidden during the entire study. All subjects were given a list of probiotic foods and supplements available in the market to ensure that no forbidden products were consumed. The Human Ethics Committee of Beijing Chaoyang Hospital approved the study protocol. All subjects provided written informed consent.2.3. Sample size and randomizationSubjects (136) were screened, randomized and enrolled; 67 subjects completed each group with one dropout per group. Subjects were assigned to the groups randomly by the physician and the intervention began immediately following randomization. The subjects, the investigators, the physicians, the study nurses and other study personnel were blinded using randomization codes and were kept confidential until the end of the data analysis. With a power of 80% and at a significance level of 0.05, the difference between the groups would be statistically significant with 60 subjects per group.