Microbiome · 12 August 2026 · 6 min read
The gut, briefly
Thirty-eight trillion organisms, a job description, and the three things that actually move them.
You are carrying roughly as many bacterial cells as human ones. They are not passengers. They finish the digestion your own enzymes cannot, manufacture a share of your vitamin K and several B vitamins, train the immune cells that line the gut wall, and produce short-chain fatty acids that the cells of your colon use as their primary fuel.
What actually changes the population
Three things, in order of effect. Fibre, because it is the substrate almost every beneficial genus ferments and the average intake is roughly half of what it should be. Antibiotics, which reset the population in days and take months to recover from. And sleep, whose effect is smaller than the first two but far larger than most people expect.
Everything else — the fermented drink, the cold plunge, the elimination diet — is downstream of those three, and mostly noise beside them.
Where a synbiotic fits
A probiotic adds organisms. A prebiotic feeds the ones already there. A synbiotic does both, which matters because organisms arriving into a colon with nothing to eat do not stay long. The question is never whether a strain is beneficial in a dish. It is whether enough of it arrives, and whether there is anything there for it when it does.
The honest caveat
Microbiome science is young and a great deal of what is confidently said about it is ahead of the evidence. We try to say only the parts a human trial has actually shown, which makes for shorter copy and better products.
