Dr. Will Bulsiewicz

So that means they can actually impact the physiology in your body.

These chemicals, by the way, are often produced by your gut microbes.

70% of your immune system exists in your gut.

And the immune system is able to activate things that can affect the entirety of your body and create inflammation.

Also your hormones and your neurotransmitters that are produced in your gut.

So it's interesting when I finished medical school in 2006, I had learned about serotonin and things like this.

And I didn't realize that there's over 30 neurotransmitters.

I didn't realize there's that many.

I thought there were like six.

There's over 30 neurotransmitters.

They are produced in the gut.

90 to 95% of serotonin is produced in the gut and 50% of dopamine is produced in the gut.

And so now these things can have influence in the gut, but also throughout the body.

And particularly with serotonin, I just want to be totally clear because there's going to be someone who's a scientist who's going to want to make sure that I'm clear on this.

The serotonin that's produced in your gut does not actually cross into the brain, but there's a precursor to serotonin.

called 5-hydroxytryptophan.

And this 5-HTP actually has the ability to cross into the brain and signal and change how your brain works.

And then the last but not least, perhaps the biggest and most important, is a pair of nerves, which are probably my favorite nerves in the entire body, Jonathan.

called the vagus nerves.

All right, now the vagus nerves start in our brain, pass through our skull, and descends down to our gut.