this is something that i have never heard of. i did try kefir a few years ago and I had a horrible reaction to it. But that is because i am allergic to cow's milk. After just 3 months I became allergic to goat milk.
i had such a bad reaction to the kefir that i am wondering if it had to do with some of the yeast fermentation that takes place with respect to kefir.
i used to ferment saurkraut but even that got to me. later i learned that it is very high in yeast.