Morbid obesity has become a major global health problem, and the use of bariatric surgery is increasing. One common complication seen following bariatric surgery is the formation of gallstones. Contributing factors to gallstone formation include hypomotility of gall bladder and supersaturation of bile due to rapid weight loss and mobilization of cholesterol. Previous studies revealed oral probiotics could reduce the cholesterol level by as much as 22% to 33%. The possible mechanisms included bile salt hydrolase activity, assimilation of cholesterol by the bacteria, binding of cholesterol to the bacterial cell wall and physiological actions of the end products of short chain fatty acid fermentation. Therefore, the aim of this study was to determine the ability of probiotics to prevent gallstones formation after bariatric surgery and to evaluate the impact of oral administration of probiotics on the post bariatric surgery patients 's quality of life.

Gastrointestinal Quality of Life Index is a widely accepted questionnaire for evaluating the quality of life for patients receiving bariatric surgery. It consists of five domains: digestive symptoms; physical function; emotional condition; social condition and effect of medical treatment, which could access the quality of life of bariatric patient effectively and completely.

Inclusion Criteria:

1. Patients receiving bariatric surgery for morbid obesity
2. Patiets at ages between 20 to 65 y/o
3. Patients willing to follow up regulary after bariatric surgery.

Exclusion Criteria:

1. Patients having gallstones before bariatric surgery
2. Patients refusing taking probiotics or refusing regular follow up after bariatric surgery