# Prebiotics

A prebiotic is food for your good gut microbes. The official definition comes from ISAPP (the International Scientific Association for Probiotics and Prebiotics). It is a substrate that your microbes selectively use to give you a health benefit. That definition is deliberately broad. It covers fermentable fibers like inulin, fructooligosaccharides, and galactooligosaccharides. It also covers some non-carb compounds and uses beyond the gut. And it demands proof of two things. First, that microbes selectively use it. Second, that it gives a real health benefit. Well-studied prebiotics reliably grow Bifidobacterium and Lactobacillus species. They also boost short-chain fatty acids (SCFAs) and firm up stool. Effects on harder outcomes, like blood-sugar control and immunity, are modest and show up only in some trials. A prebiotic is also not the same as fiber in general. Fiber is fermented broadly by many microbes. A prebiotic has to clear that stricter 'selective' bar.

## Sources

- Gibson GR, Roberfroid MB. (1995). Dietary modulation of the human colonic microbiota: introducing the concept of prebiotics. Journal of Nutrition. https://doi.org/10.1093/jn/125.6.1401

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_Canonical: https://longevity-switzerland.com/en/glossary/prebiotics · Part of Longevity Cities · Updated 2026-06-22_