Overall , 179 adults with irritable bowel syndrome ( Rome III criteria ) were randomized to receive once daily 500 mg of Saccharomyces cerevisiae , delivered by one capsule ( n = 86 , F : 84 % , age : 42.5 12.5 ) , or placebo ( n = 93 , F : 88 % , age : 45.4 14 ) for 8 weeks followed by a 3-week washout period .