I had symptoms of IBS for five years. I was finally diagnosed by the neurologist with low Vitamin B12. I was prescribed sublingual Methylcobalamine, 500 mcg. daily. It has been three months and I am 90% normal. I am still careful by avoiding milk, although I can eat ice cream and cheeses now, as before my illness. I still have to watch the fruit, although that is improving also as I was able to tolerate a nectarine the other day. I am looking forward to more improvement, but I thank God and the neurologist every day that I no longer suffer from gas, bloat, constipation, incomplete evacuation, pain, vertigo, nausea. I am able to lead a normal life now.
Of course, not everyone with IBS has this deficiency, but my story warrants looking into that. Taking Vitamin B12 when you are not deficient can cause a lot of problems so you must be diagnosed by two lab tests to confirm it -- one for Vitamin B12, and if it is low or borderline, a test for high Methylamonic acid.