Is IBS caused by an imbalance of the intestinal bacteria?
In fact, as reported by Huffington Post UK in May of 2012, "The results of a new Cedars-Sinai study suggest that an overgrowth of bacteria in the gut has been 'definitively linked' to Irritable Bowel Syndrome (IBS)." There are several other studies that link inflammatory bowel diseases with the gut microbiota (the term used to describe the intestinal bacteria as a whole).
Does that mean that kefir can cure Crohn's Disease or IBS?
No it does not mean that kefir will cure anything. There is compelling evidence that some of the probiotics that occur naturally in kefir can help resolve symptoms of IBS. Studies such as this one show that certain bacterial strains (in this case a type of Lactobacillus, which is found in fermented products such as kefir) did completely resolve the abdominal pain associated withIBS.
A study of a different strain of Lactobacilli used in children with antibiotic resistant enterococci infection showed that "LGG supplementation temporarily eliminates the VRE carrier state and increases gastrointestinal counts of Lactobacillus spp. in children versus placebo."
More study is needed, however, in the meantime it is my opinion that kefir falls under the umbrella of "Could Help, Can't Hurt". if you could make something for pennies a day that would give you a boost in nutritional status, improve immunity against disease, and COULD reduce or remove intestinal inflammation… why wouldn't you?