Prebiotics
Food compounds (generally fibres or carbohydrates) that humans cannot digest but beneficial gut bacteria can ferment, promoting their growth.
Prebiotics are not micro-organisms but nutritional substrates for beneficial bacteria. The most common are inulin, fructo-oligosaccharides (FOS) and pectin. Unlike probiotics, prebiotics survive passage through the stomach and reach the colon intact, where they are fermented.
Fermentation produces short-chain fatty acids (SCFAs), notably butyrate, which:
- Feeds the cells of the colon (enterocytes)
- Strengthens tight junctions (helps prevent leaky gut)
- Regulates gut inflammation
- Provides energy for the brain (the gut-brain axis)
A fresh angle: natural prebiotics have been in fermented foods since the Neolithic: onions, garlic, asparagus, leeks (fructans), green bananas (resistant starch), and pulses cooked and cooled. But modern life has reduced prebiotic intake (less fibre, and ultra-processed foods destroy prebiotics).
A trap: adding too many prebiotics too quickly can cause bloating and wind (excess fermentation). Increase gradually (“go low and go slow”) and combine with probiotics for a synergistic effect (= synbiotics).
Postbiotics (metabolites produced after the probiotic ferments the prebiotic) are also emerging as important for health.