Fermented foods have been a cornerstone of human diets for thousands of years. They are the richest natural source of probiotics — beneficial live microorganisms.

Common fermented foods:

• Yogurt — Lactobacillus and Bifidobacterium. Most studied. Look for "live active cultures."
• Kefir — fermented milk, more diverse cultures than yogurt
• Kimchi — fermented cabbage and vegetables. Also high in fiber and vitamins.
• Sauerkraut — fermented cabbage. High in vitamin C and K.
• Miso — fermented soybean paste
• Tempeh — fermented whole soybeans — complete plant protein
• Kombucha — fermented tea. Some benefits but often high in sugar.

Evidence for probiotics:

• Strong: Reduces antibiotic-associated diarrhea, improves IBS symptoms
• Emerging: Mental health, immune function, weight management
• Strain-specific — not all probiotics have the same effects

Reference:

Wikipedia: Fermented food

https://en.wikipedia.org/wiki/Fermented_food