1 · The gut microbiome · an inner ecosystem
About 38 trillion microbes live in your colon as symbiotic partners, breaking down fiber you cannot digest, making vitamins, training the immune system and maintaining the gut barrier.Your colon hosts ~38 trillion microbes (Sender 2016 corrected the old '10× more bacteria than human cells' claim; actual ratio ~1:1), spanning 1000+ species, with 150× more genes than the human genome.They are not 'tenants' but symbiotic partners: you feed them, they digest what you can't (fiber), synthesize vitamins (K/B-complex), train the immune system, and maintain the gut barrier.