Probiotics Are Mostly A Waste of Time, Except...

There is an area of research which has long hoped to be the linchpin in understanding human health: bacteriology. Different microbes play variant roles in human health. Since we know that different bacteria affect us in multitudes of ways, it wasn’t a far cry to believe that proactively eating probiotics was a good idea.

Between supplements and fermented foods, we went gaga for the highest and broadest count probiotics, yogurt, kefir, kimchi, and so forth. Unfortunately, the continuation of research found no measurable positive outcomes, in part because most (over 90 percent) of the bacteria in the human body is anaerobic (thus necessitating fiber to proliferate) and also because all of the popular strains are destroyed by stomach acid and bile. Any benefits people received from sauerkraut likely had more to do with the fiber content, not the trillions of probiotics therein.

It’s a complex subject which dodges about any time someone tries to make a grand sweeping generalization. Some otherwise benign strains become very damaging to human health when they are out of balance. It isn’t as simple a subject as “good” and “bad.”
That all said, more discoveries are afoot; and it appears that spore-based probiotics (these are strains with the genus Bacillus), even when encapsulated and taken as a supplement, DO show promise to beneficially affect humans:

https://www.wjgnet.com/2150-5330/full/v8/i3/117.htm

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In human and other animal studies we have found definitive causal relationships between gut bacteria and obesity, anxiety, autoimmune diseases, etc. Many people hoped we could, therefore, just swap in and out certain strains and all would be well. Perhaps one day. For now, it’s just a fair bit more complicated than that.

Nonetheless, people who are struggling in various domains of health and fitness wouldn’t be ill-advised to run experiments with fiber and modest intake of spore-based probiotics. Both have reproducible and reproduced scientific findings to back them.
The more popular strains in supplements and fermented foods don’t have reproducible outcomes, are mostly a waste of time, and in some cases prevent the proper recolonization of healthy gut bacteria:
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https://www.google.com/…/2178860-probiotics-are-mostly…/amp/