rationTracker

Foods for Gut Health: Fiber, Fermented Foods, and What the Data Shows

The fiber and fermented foods tied to a healthier gut microbiome, ranked from measured data.

Written by Ration Editorial Team · Updated July 19, 2026

Key takeaways

  • Dietary fiber is the single most consistent lever for gut-microbiome diversity.
  • Fermented foods add live microbes and, in one trial, lowered inflammatory markers.
  • Variety of plants matters more than any single "superfood".

Fiber feeds the microbiome

Fiber is the part of plants humans cannot digest, so it reaches the colon intact and feeds gut bacteria, which ferment it into short-chain fatty acids.

Higher fiber intake is repeatedly linked to greater microbiome diversity, a marker of gut health.[1] Most people eat far less than the daily target.

These are the highest-fiber foods per 100 grams in the database:

Fiber, g per 100 grams
  1. 1Corn Bran Crude79 g / 100 g
  2. 2Gums Seed Gums (Includes Locust Bean77.3 g / 100 g
  3. 3Wheat Bran Crude42.8 g / 100 g
  4. 4Carob Flour39.8 g / 100 g
  5. 5Sorghum Bran White35 g / 100 g
  6. 6Seeds Chia Seeds34.4 g / 100 g
  7. 7Flour Coconut34.2 g / 100 g
  8. 8Peppers Hot Chile28.7 g / 100 g
  9. 9Seeds Flaxseed27.3 g / 100 g
  10. 10Peppers Pasilla26.8 g / 100 g
  11. 11Chives Freeze-Dried26.2 g / 100 g
  12. 12Rye Flour Dark23.8 g / 100 g
Ranked by fiber per 100 grams (so dense, dry foods like flours rank high). Computed live from the Ration database.

Fermented foods

Fermented foods such as yogurt, kefir, and sauerkraut deliver live microbes.

A Stanford trial found a diet high in fermented foods increased microbiome diversity and lowered inflammatory markers over ten weeks.[2]

Researchers are also testing new ways to protect these live microbes so more of them survive digestion.

One study encased probiotics with phycocyanin, a blue pigment from spirulina, inside tiny protective fibers and found this raised probiotic survival and gave the mix extra antioxidant activity.[4]

Plant variety

The American Gut Project found people eating more than 30 different plant types per week had more diverse microbiomes than those eating fewer than 10.[3] Range beats repetition.

Bottom line

Raise fiber toward the daily target, rotate a wide range of plants, and add a daily fermented food. You can sort every food by fiber in the spreadsheet.

Sources

  1. Makki K et al. The impact of dietary fiber on gut microbiota. Cell Host Microbe. 2018. · PMID 29902436
  2. Wastyk HC et al. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021. · PMID 34256014
  3. McDonald D et al. American Gut: an open platform for citizen science microbiome research. mSystems. 2018. · PMID 29795809
  4. High-speed electrospinning of phycocyanin and probiotics complex nanofibrous with higher probiotic activity and antioxidation · PMID 37087274