The purpose of this study is to evaluate the effect of "combined probiotics" to improve the gastrointestinal function and intestinal bacteria flora

Probiotics were known to improve gastrointestinal function before. This is a single-blind placebo control clinical study. We will perform gastrointestinal function questionnaire and collect stool as baseline data before the study (0-week). Then healthy subjects will be randomized to two groups.

Experimental: probiotics 1 pack bid for 3 weeks. Probiotics : (AB-kefir)：Lactobacillus acidophilus,Bifidobacterium longum,Lactobacillus paracasei,Lactobacillus rhamnosus,Lactobacillus fermentum,Streptococcus thermophilus,Lactobacillus helveticus,Kluyveromyces fragilis. Other components include starch,oligosaccharide,yeast powder, superior standard spice， calcium pantothenate， VitB1， VitB12， biotin and folic acid.

Placebo group: placebo 1 pack bid for 3 weeks. Placebo: Except the probiotics (AB-kefir),the other components are the same with study group.

Then gastrointestinal function questionnaire and stool collection will be performed at the end of 1st, 2nd, 3rd, and 4th weeks after starting the study.

Inclusion Criteria:

• Healthy people who are aged between 20 and 40 years

Exclusion Criteria:

• 1. People who use probiotics medication and food that can inhibit bacteria growth within one month before the study 2. People who have active infection 3. People who have active or chronic gastro-intestinal disease 4. People who have diarrhea within two weeks before the study 5. People who are drug or alcohol abuser 6. People who are poor compliance