A few years ago I started making and eating a lot of fermented foods for purely gastronomic reasons, including kefir. I haven't really noticed any obvious changes.

I've been on antibiotics twice in this time and do feel like I get my appetite back more quickly after stopping them now. An antibiotic course used to mean weeks or months of poor appetite, nausea and indigestion now it's like 10 days. But that could be coincidence or something else entirely, who knows.