Probiotics? Sooo yesterday! Sometime last year I sourced a 100g block of fresh yeast selling for €0.45 in our nearest Polish deli. That's a bargain: it's good for about 2 weeks of baked goods Chez Bob. It's also a pathetic sale for the hard-work Poles who run the shop, so I always buy something else: rye flour, cherries and kefir are often in the basket when I check out. None of these are normally on shopping list but they get chugged down in some form or another. During the brief time last year when travel was permitted, Dau.II and The Pep, her S.O., came to visit and we picked up yeast and kefir on the way home. Turns out that Pep is partial to a glass of kefir if it's put in front of him, so there was no difficulty in finishing the bottle.
Last week I was talking
shite groceries with Dau.II and I reminded her that any Cork Polski Sklep would have yeast and kefir. And she made some comment about the kefir having probiotic benefit for her bloke. I demurred: the microbes in kefir [or yoghurt, creme fraiche, koumiss] would be a monoculture which probably wouldn't survive the acid gauntlet of Pep's tum and wouldn't cause a blip on the make-up of his intestinal flora. What we all need, I asserted, was prebiotics: the foods [mostly plants, not too much] which encourage the growth of a diverse, robust and mutually supportive community down there.
There are two scientific angles on this.
1) Each species will have its own characteristic, unique community of microbes, some of which will arrive viable in the digestive tract. You want to provide the biggest choice of candidates for a new dimension of microbial biochemical capability to get established inside. Because your flora is different from mine and that of your roomies / bed-fellows; although your floar will be shared with your 'family'. This could be why herbal remedies appear to work for some people some of the time: that plant provides a key to this locked gut.
2) Each plant species has wildly different ability to absorb and concentrate particular minerals: not only lithium, but potassium, calcium, selenium, lead, cadmium. Minerals need to be available in just-so concentrations and dietary intake is one way to keep particular elements above baseline and usable by the complex system of interactions which is human physiology.
Look after the food and the pro-biotics will look after themselves. And let's not forget the viruses.