Professor Tim Spector

They convert that fiber into products such as short-chain fatty acids, which are the really beneficial chemicals that are good for our immune system.

And it's important to realize that across both the small and the large intestine, you've got

Huge amounts of nerves.

You've got what's called the enteric nervous system, which is our second brain.

And it was actually the first brain to be formed.

So when we were little embryos, we started as a little tube.

And the nervous system that formed around our intestine was actually the first brain of our body.

And in a way, we developed the second one on our head as a bit of an afterthought, which is quite a fun way of thinking about it.

But it just shows how important the nerves are

in our gut to the way we function.

And as we were talking earlier about this connection between the two.

And there's also immune cells.

So 70% of our immune cells are in the gut, most of them in the large intestine, but also in the small intestine.

So our immune system is here and a huge amount of our nervous system is here.

Why?

They're everywhere.

So they're also in your... Yes, I should point out we're covered in bugs.

So every bit of the human body has some bugs in it.

The second biggest place where we have them is in our mouth.

So the oral microbiome in our saliva and in our teeth and our gums.