The healthiest bug in your gut has no name — it has a filing code
Scientists went looking for the one thing healthy guts share worldwide. They found it. And it's a bacterium nobody has ever grown, watched, or put in a pill.
This bug has no name. What it has is a code from a database: CAG-170.
A Cambridge team read the DNA in stool samples from 39 countries. This nameless thing kept turning up — plenty in well people, thin in sick ones. So how does something that common stay invisible? One number tells you.
Cambridge went digging in that unmapped two-thirds. One group of bugs jumped out.
The same bug ran low in all 13 illnesses they checked
Dr. Alexandre Almeida and his team at the University of Cambridge pooled 11,115 gut samples. They counted 4,612 species living in there. Of those, 3,067 had never been logged in a human gut before.
Then they matched the samples to health records. CAG-170 sat high in healthy people and low in every illness on the list — Crohn's, obesity, bowel cancer, Parkinson's, 13 in all. That pattern held whatever the country and whatever people ate.
Which raises a fair question. What does a bug nobody can grow do down there to matter that much?
It runs a vitamin B12 shop for the other bugs
Its DNA holds the full build instructions for vitamin B12, start to finish. That's rare. B12 is a beast of a molecule, and only microbes can make one from scratch.
Plenty of good gut bugs need B12 but can't make it, so they borrow and scrounge. CAG-170 makes it in bulk and hands it out, and dozens of neighbors run on that supply.
It carries a second toolkit: enzymes for chopping a broad range of plant fibers. Oat husk, bean skin, apple peel — each fiber needs its own tool, and this bug holds most of them.
So it cooks for the block and stocks the pharmacy. Big job for something with a serial number instead of a name.
CAG-170: 13 species, never grown, not for sale
The code is as dull as it sounds. CAG means co-abundance gene group: bits of DNA that always show up together, so a lab knows it's one creature without ever holding it. The 170 is the slot it landed in.
Behind that code sits a whole new genus in the Oscillospiraceae family. Thirteen species, eleven of them tied to good health.
Nobody has grown one. Bugs like this die within minutes of meeting air, so raising them needs a dish that copies the inside of your colon… and science is not there yet.
Which means the supplement shelf can't sell it to you. Almeida said it plainly: the probiotic trade still pushes the same few species it did decades ago. You can't buy this one… so you feed it.
Feed it the way it eats: many fibers, not more of one
A bug built to chop many fibers does badly on a diet of one. Variety is the lever, not volume. In the American Gut Project, people eating 30-plus kinds of plants a week carried far more varied gut bugs than those under ten.
Each new plant brings a fiber the last one didn't. Four cheap ways to widen the menu:
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Pearl barley Beta-glucan, a gluey fiber wheat won't give you |
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Raspberries Seeds and skin your own enzymes can't open |
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Split peas A dollar a bag, and a fiber mix beans skip |
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Mushrooms Beta-glucan again, built in a shape grains lack |
One shopping trip won't hold it. The habit that does takes no planning.
Add one plant you haven't eaten in the past week
Pick one plant type you haven't touched in seven days. Put it in a meal today. Herbs, seeds and spices count, so a spoon of parsley on the eggs earns a point. Do that most days and you'll clear 30 plant types a week without tracking a thing.
| 🚫 The same three vegetables on repeat | ✅ One plant type you skipped all week |
Your gut's best bug sits on no shelf. It sits on your shopping list.
The best bacteria in your gut can't be bought.
Hand them a new plant and they show up on their own.
B12 is the one vitamin that neither plants nor animals can build — microbes make all of it on Earth. Your gut bugs brew plenty in the colon, but your absorption gear sits upstream in the small bowel. So most of it goes to them, not to you.
