A Tie in Your Tummy
A famous 'fact' about germs turns out to be a 1972 guess, and the real story is more useful: what we eat shapes the microbes in our gut, and a couple of simple habits may help.
- • Sender, Fuchs and Milo (2016) estimate about 38 trillion bacteria and 30 trillion human cells in a 70 kg man, roughly 1.3 to 1; about 90% of our cells are blood-lineage cells. The old 10:1 figure came from Thomas Luckey, who scaled up across the whole one-litre gut when most bacteria live in the 0.4-litre colon.
- • In the American Gut Project, over 10,000 volunteers, the number of different plant types eaten was linked to gut microbe diversity, more than labels like 'vegan'; the authors say this self-selected group means results should be treated with caution.
- • In a 2021 Stanford trial of 36 adults, 10 weeks of fermented foods raised microbe diversity and lowered 19 inflammatory proteins, while a high-fibre diet did not raise diversity in that time. High-fibre diets are still linked to lower death rates.
Are you more germ than human?
People said you carry ten bacteria for every one of your own cells. That came from one quick sum in 1972. He counted germs as if they filled the whole tube from mouth to bottom. But most live in one short part near the end.
In 2016, scientists counted again. About 38 trillion bacteria. About 30 trillion of you, mostly tiny red blood cells. Roughly a tie! One trip to the toilet may flip the score.
So if it is a tie, half the team is yours to feed.
Step one: you cannot digest some plant parts. Step two: your gut microbes can, and different microbes have tools for different fibres. Step three: so more kinds of plants may feed more kinds of microbes.
A huge study found people eating over 30 kinds of plants a week had a wider mix of microbes than those eating under 10. A link, not proof.
A small trial gave adults fermented foods like yogurt and kimchi for ten weeks. Their microbe mix grew. And 19 signs of the body on alert went down. The twist? An extra-fibre group barely changed. Maybe ten weeks was too short.
Try two things: eat many different plants, and add yogurt or kimchi.
So, how many plants have you eaten today?