The trial worth knowing
Researchers randomised healthy adults to either a high-fiber diet or a high-fermented-food diet for ten weeks, measuring microbiome composition and 93 inflammatory proteins.
The fermented-food group showed increased microbial diversity and decreased levels of nineteen inflammatory proteins, including interleukin-6. The high-fiber group showed no overall diversity increase in that window, though people who already had diverse microbiomes responded better to fiber.
The honest interpretation: fiber feeds what you have; fermented food appears to broaden what you have. Ten weeks may simply be too short for fiber's slower remodeling to register.
What counts as a fermented food
Live-culture yogurt and kefir. Sauerkraut and kimchi from the refrigerated section, not the shelf-stable jar that was pasteurised after fermenting. Miso and tempeh. Kombucha. Traditional pickles brined in salt, not vinegar.
Heat kills the cultures. Stir miso into soup off the boil; add kimchi at the end of a stir fry, not the start.
Where supplements fit
Specific strains have solid evidence for specific jobs, preventing antibiotic-associated diarrhea, for example. Buying a generic multi-strain capsule for general wellness is a much weaker proposition, and most strains do not take up residence.
Food gives you cultures plus the matrix they arrived in: protein, fiber, organic acids, and bioactive peptides. That combination is hard to bottle.
