Add a daily fermented food

Live-culture yogurt, kefir, kimchi, or sauerkraut — one serving a day introduces bacteria the gut-brain axis runs on.

Why it works

Fermented foods containing live microorganisms transiently colonize the gut and provide fermentation metabolites (lactic acid, bioactive peptides) that feed native beneficial species. A randomized trial compared a high-fermented-food diet with a high-fiber diet and found the fermented-food group showed greater increases in microbiome diversity and greater reductions in 19 inflammatory proteins — including those implicated in neuroinflammation.

How to do it

1. Choose a fermented food you actually enjoy — adherence matters more than which species is in it.
2. Buy live-culture versions: refrigerated sauerkraut, kefir, full-fat plain yogurt with "live cultures," or kimchi.
3. Start with a small portion (2–3 tablespoons of sauerkraut or one cup of kefir) alongside a meal.
4. Pair with prebiotic fiber to feed the introduced bacteria and extend their effect.

Evidence

A randomized trial found a fermented-food diet increased microbiome diversity and reduced inflammatory markers over 10 weeks, compared to a high-fiber control diet. (rct)

The outcome measure was inflammation and microbiome diversity, not mood directly. The mood link requires an additional inferential step through neuroinflammation.

Sources

• Wastyk et al. (2021), gut-microbiota-targeted diets modulate human immune status, Cell

Common mistake

Buying shelf-stable, pasteurized "sauerkraut" or "pickles" — the heat processing kills all live cultures. Only raw, refrigerated, unpasteurized versions contain viable bacteria.