This article gave an interesting classification of fermented foods, pointing out that with some, like bread and wine, we eat the products of fermentation without the living organisms, while with others like kefir and yogurt, we eat the viable critters also.
Lactobacilli are called probiotics, and are supposed to have health benefits. It is not proven that they do, but at least the lactobacilli use up some of the sugar we would otherwise be eating, and taste good.
The problem with the claim that they diversify and benefit our microbiome, and crowd out the bad germs, is that they do not generally attach to our intestinal walls, and go right through with the rest of our food. They don’t stick around long enough to do any good.
My late wife had a bad infection with a bad actor called Clostridium difficile, which caused her to have a severe, bloody enterocolitis. After the second hospitalization with this affliction, an Infectious disease doctor suggested “culturelle”, which contained a patented Lactobacillus rhamnosus GG, which WAS supposedly proven to attach for a while. My wife took this, and never had another attack.
I still take this daily, “on faith”. Gullible me. Fecal transplants are now used effectively for C. Dif. enterocolitis. Avoiding unnecessary antibiotics, which wipe out your normal microbiome, your “good guy competition”, is An even better idea, but seems risky.
BOTTOM LINE: Kefir and yogurt are calorie depleted, and taste good. What is not to like?