Traditional, minimally processed, fiber-rich diets sustain a diverse microbiota shaped over millennia, which a Western diet can narrow within a single generation.
For millennia fermented foods have delivered live microbes and beneficial metabolites to the gut, working best alongside a fiber-rich diet.
Caffeine cuts both ways: in moderation and early in the day the polyphenols in coffee and tea support the microbiota, but excess or late intake can unsettle gut balance.
Swallowed tobacco smoke reaches all the way to the gut, lowering microbial diversity and butyrate production and weakening the gut barrier — but quitting sets gradual recovery in motion.