All language subtitles for R.I.L.S2024E01.WEB-DL_track3_[eng]

Every time you put
food in your mouth,

you set your body's
defences onto high alert,

and anything that makes
it past those defences is...

Give me that.

...is entering
a biological food processor.

Will you stop that?

Now, this happens
every time you eat,

and normally you don't even
think about it.

But that changes tonight, because...

...tonight, we're heading
down the tube.

Oh...

Oh, dear.

APPLAUSE

Zach, can I get rid of that?

Welcome!

Welcome to the Christmas Lectures
from the Royal Institution,

supported by CGI.

I'm Chris van Tulleken,
and I'm going to be showing you

why food matters.

It matters because it's what
we build ourselves from,

and it matters as our fuel.

But I'm also going to be
demonstrating how,

when one ape started to process
food outside its body,

it changed everything,

from our anatomy and physiology,
to our culture,

and everything about the surface
of planet Earth as well.

Now, today, we're going
on a short journey.

It's just seven metres long,

and you can see that journey
here on this perfect,

accurate representation of me.

This is what I look like
without my clothes or my skin.

As you can see,
it's all muscle under the shirt.

And we're starting in my mouth
and we're going to the other end

via the oesophagus, the stomach,

the duodenum, the jejunum,
the ileum.

Then we get into the colon,
the ascending colon,

the transverse colon, the descending
colon, into the rectum,

and out the other end.

And this tract,
this gastrointestinal tract,

is where our food is broken down,

and then absorbed and, of course, transformed.

We are going to need a few
gross alerts along the way.

Now, eating is a hazardous business,

because you will all know one of the
first things you learn in biology

is that a central project
of all life

is to keep the outside outside,
and the inside inside

and not to get them mixed up.

So putting things
inside the tube is risky.

It comes with the risk of microbes,
pathogens, toxins,

and so the entrance
to our gastrointestinal tract

is extremely tightly guarded.

And the defences begin when you even
just start thinking about food.

So I want you all to think
about eating something really sour,

like a lemon.

Now, can you feel the saliva
pooling inside your mouth

as you think about eating
this acidic food?

To help us now explore

the defences that are
at the beginning of the tube,

all of them, I want you to welcome

Associate Professor in Public Health
at University College London

and, of course, my identical twin
brother, Dr Xand van Tulleken!

APPLAUSE

I said...
I said to come dressed as a lemon.

Can we... It was all they had.

Can we start by having a look
in your mouth

using the special rhinolaryngoscope
that you're skilled at using?

Now, provided you have at least
six years of postgraduate

medical training
and a rhinolaryngoscope,

you can do it at home.

Now, what Xand is going to do,
can you just demonstrate?

I'm going to hold this here...
You do it.

Trying not to touch the end.

Endoscopes, of which this is one,

are fibre optic cameras

that doctors and other clinicians
can use to look inside your body.

We can put them up the back passage,
we can put them down your throat...

LAUGHTER
...but this is a very...

Which we're not going to!
Well, maybe we will!

Let's not give any spoilers.

And if you see there,
there's a light on the end of it,

and Xand has a controller

so he can move the end to look
around corners in the body.

The first thing we're going to do
is have a look in Xand's mouth.

The first thing you see
are the lips.

Lips are incredibly sensitive,

and you can detect lots of toxins...
LAUGHTER

Just get on with it, Xand.
Put it in your mouth.

So, as we go into Xand's mouth,
we can see at the back of the mouth

two white scars from where
Xand had his tonsils out.

The dangly bit is the uvula.

And, let's have a look now
at the surface of your tongue.

Put it right down. Yeah, nice.
Nice.

That's a lovely view.

Now, you can see the buds
on Xand's tongue.

What are those buds?

Do any of you know?

Taste buds!

They are not taste buds.
They are papillae.

Now, your taste buds
are inside your papillae.

Your papillae are buds,
your taste buds aren't buds -

they're more like little pits.

They're so small you can't see them,

and they're collections
of very specialist cells.

So it's a bit confusing,
but the papillae -

all the rough lumps and bumps -
that is where we find taste buds.

OK? And your taste buds are

sensors that detect the chemical
properties of your food,

and they send information
to your brain,

and then you can decide
whether you want to receive it,

swallow it, or if you want
to reject it.

Now, your mouth
is also a chemical factory,

and, Xand, I want to put in...

I'm going to let you pick
your tomato.

Oh, you pick... OK. You pick.

Maybe a small one.

Now, I want to show you first,

but don't... don't... don't
chew it just yet.

OK, so we've got the tomato
in the mouth.

Now, you can see, I want you
to see this perfect sphere

at the back of Xand's mouth.

This is potentially covered -
it might be full of poisons.

Not all red berries are safe.

So, Xand, I want you to move
it over to your molars,

bring it to the side of your mouth,

and we're going
to see if we can film Xand

with the first stage
of breaking down food,

the mechanical destruction of food.

Because your body destroys
food in two ways,

mechanically and chemically.

And here we go.

So, Xand's going to apply pressure.

There we go.

Very skilfully
not biting his tongue.

He's mixing it... Or the endoscope!

Or the endoscope!
Don't bite the endoscope.

That's the main thing.
We cannot afford to buy a new one.

He's mixing it with saliva.

Now, you make a litre and a half
of saliva every day.

You make about this much.
You're swallowing it constantly.

And saliva is amazing stuff.

So, whilst he's mixing
the tomato with the saliva,

it's going to lubricate the tomato.

It's full of chemicals called mucins
which make it slippery and slimy.

It's going to clean the tomato.

It's got chemicals and antibodies
to kill pathogens, microbes.

It's also got, um, enzymes

that start digesting the food
in your mouth.

They break down starches
and fats, amylases and lipases.

And, finally, it's got chemicals
that neutralise the acids

in the tomato so that they
don't damage Xand's teeth.

And Xand, I think you are now ready

there we go, dismantled,
partly digested tomato.

Xand, big round of applause.
Thanks very much.

Give it a swallow.

APPLAUSE

So, salivation
is just one of the responses

that our bodies make in order
to prepare us to receive food.

There are all kinds of other
physiological changes that happen

when you smell food, you think
about food, you see food,

or you interact with food
in any way.

But, what if the food on our plate
doesn't match

our expectation of what
we've been led to believe it is?

Well, to help us explain that,

I want to invite National Treasure,

legendary chef, and judge
on the Great British Bake Off,

Dame Prue Leith!

APPLAUSE

Are you there, Prue?

Oh! How are you doing?

CHEERING AND APPLAUSE

This is very good, because

you've prepared us a bit of
Christmas dinner here, haven't you?

Ah, well, it's Christmas!
It's the Christmas lectures!

This is turkey.

You've got some... A standard
turkey? Turkey, veg, spuds.

Great, OK.
Tell me about food appearance -

is it important, or do you just
have to get all the flavour right?

Well, the flavour is important,
but I tell you what,

chefs always say
you eat with your eyes

because they know perfectly well

that if you don't like the look
of food, you won't try it.

So I do think that chefs are...
Sometimes they're obsessed

with the way food looks
and they overdo it,

and forget that flavour
actually matters more.

But we have to get past that -
probably the first line of defence

is smell, and the second is
going to be sight. Absolutely.

You've got to get past
these defences at the entrance

to the tube. OK. Shall I reveal?

This is a classic turkey dinner...
And you've got some gravy.

You need a bit of gravy. You're
going to put a splash of gravy on.

A bit of gravy on it.
Now, can I get a volunteer?

I'm going to take you
just cos you're on the end.

Come on. Come on down.
What's your name?

Zavi. Zavi?

Come on down, Zavi.

Big round of applause for Zavi.
Come in the middle.

APPLAUSE

Zavi, are you up for trying a bit
of Prue Leith Christmas dinner?

Yes, definitely. Brilliant stuff!

OK. Actually we're going to get Zavi
to try this one, is that right?

Yeah. This one, yes.
This one, I've doctored a bit.

You've doctored it a little bit.
Yes. OK. Zavi, this is the meal

we want you to try,
or contemplate trying.

OK? There we go.

MURMURING

Now, a little bit of wincing
from around the room.

Doesn't look quite right, Prue,
I've got to say.

Well, it's... Are these potatoes
that are blood red?

Yes, they're potatoes,

and that's turkey,
and that's carrots.

The black stuff is carrots.

And the brown stuff is sprouts.

And the bright green stuff
is turkey.

OK. You like...
Zavi, you like turkey?

Yes. There you go,
there's a knife and fork.

Are you brave enough to try that?

I would definitely rather eat...
You'd rather eat that?

OK, well, why don't you try
the green stuff anyway?

So, Zavi's a bit disgusted,

but he is able to overcome
that sense of disgust

using other bits of his brain.

Well, I think he is. Are you going
to be able to do it? Go on!

How is it?

Mm. It's OK. Once you...

What does it taste like?

It tastes like turkey.
Turkey and gravy.

Right. Once you get past the eyes,

the fact that Prue has coloured
the turkey bright green

is neither here nor there.

But it really, really puts
you off, doesn't it?

OK, Prue, do you want to serve...?

Do you want to do a bit of gravy
on the veg and see if Zavi wants...

I've got a bit of gravy on the veg.
Maybe a sprout? Put a bit more.

Um...

I want you to taste...

Can I just pick up this carrot
and put it in your mouth?

Would you...?
Would that be all right?

Open wide. Excuse fingers!

Zavi? What do you make of that?

It's very sweet.
It's very sweet.

Is it a carrot? No.

What is it, Prue?
What have you done?

It's cake. It's cake.

Is it all cake?

That's cake, and this is cake.
Look.

Oh, the sprouts are cake, too?

AUDIENCE GASPS

Oh, they're very convincing.

Can I try a... Can I try
a Prue Leith cake sprout?

Is it sprout-flavoured?

No, it's very sweet.

Hold on.

Let's cut one in half.
I just want to have a look.

I just want to show the camera
how beautiful these are.

The little leaves.

But if we cut them in half...

Zavi, do you want half a sprout?

The only slightly discomfiting thing

is that they are covered
in savoury gravy... Yes!

...which is not really what
you were expecting.

And this is sort of pink... pink
cake.

So, food exists on a knife edge
between desire and disgust,

and you can flick quite quickly
between those two states.

Prue and Zavi, thank you very much
for being such a good sport.

You can head back to your seat.

So, tiny alterations in our ideas
about food, or in the food ourselves

can shift them from being desirable
to disgusting.

So, we are going to investigate.

Do we learn to be disgusted?

Or is it something
that we're born with?

And to help me with this,
I've enlisted a real expert.

She would be with us today,
but it is well past her bedtime.

So instead we filmed her earlier
today in the RA.

This is my baby daughter, Indigo,

and she is nine months old.

We can see her there.

And Indigo is great
for doing this experiment with,

because she's hardly
tried any foods ever.

So we're going to put some foods
that you would all be disgusted by,

that none of you would want to eat,

and see if she's yet... If she has
an in-built sense of disgust.

So, the first thing
we're going to try

is some live earthworms in dirt.

So, there we go.

That's my wife, Dinah.

We've got two very severe
RI scientists

standing behind her,
collecting the data.

And so, Indigo, not...
No sign of disgust.

She's not pulling a face.
She's not distressed.

She's enthusiastically engaging
with the worms.

She's picking them up.

Now, the question is,
is she going to...

Is she going to put one
in her mouth?

Um, she's definitely not disgusted.

Now, we did do another experiment

where we gave her a hospital bowl...

...with a very convincing
large human poo in it.

Now, of course,
this is a cake made of dates.

It doesn't smell bad, but she has
no aversive reaction at all.

She's got no intellectual knowledge
about poo, about pathogens,

about infection.

To build up the memories of food
that allow us to desire them

or be disgusted by them,

for the most part,
we need to experience them,

and we need to use our senses,

and particularly our sense of taste.

There are some smells that we seem
to have an in-built dislike of,

even if we can learn
to love them eventually,

and there are some tastes
that we don't like as well.

So now, for the next demonstration,

I want to have a volunteer
with a sense of taste.

There's a young person there
in a blue top.

Yes, you.

Round of applause!

APPLAUSE

That's a good giveaway.

Now, what's your name? Abel.

Abel. Great to meet you, Abel.

Come here. Are you happy
to try some stuff?

Um, sure. We're going to
go through the five tastes, OK?

The five common tastes.
There's no tricks here.

I just want you to tell me
what you're tasting. OK?

Stick your tongue out.

I'm going to put it carefully
on your tongue.

That's good. Don't let it fall
on your top. How's that?

Salty.

Oh, it's very salty!

Was that not too salty for you?

Er, no, not that salty.
You didn't mind it.

OK, it's very interesting.

People experience tastes
in very different ways.

So for me, that was almost
as salty as sea water.

For Abel, that was just fine.

OK. And salt taste...

Let's have a go at that.

Kind of sweet. Kind of sweet?

Yeah. Not... not very sweet,
but kind of sweet.

Not very sweet. Have another go.

I didn't touch my tongue.
I'm being careful.

No double dipping here.

Yeah, it's sweet.
It's sweet, isn't it?

That's sweet taste. So salt -

very, very important to get
your salt taste right.

Too much salt, you die.
Too little salt, you also die.

Salt is one of... Sodium - one of
the molecules that keeps you alive.

Sweet. Was it nicer than the salt,
or about the same?

I mean, I have a sweet tooth,
so I'd say this sweet, sweet liquid.

Did you love the sweet liquid?

Um, not love, but I liked it, yeah.
It was fine. OK.

Good. OK. Try this one now.

Tongue right out.

OK, see what you make of this one.
Lean back a bit.

Open your mouth up. I'm going to get
it on your top... There you go.

Oh, that's sour.

Yeah, that's sour. Oh.

How would you describe that?

Extremely sour. Sour.

Very good. So, do you know
what sourness is?

Er...

It's acidity.

That's what you're measuring.

You're checking the pH of a food.

Now, almost all animals
hate sourness,

but humans are one
of the few that like it,

and it's probably because
we need vitamin C in our diet,

and vitamin C is ascorbic acid,

so it gives us a sense that
the acids can be quite nice.

And it's not that unpleasant, is it?

It's sour, but it's somewhat
refreshing.

Yes, it's not unbearable.

Stick your tongue out, Abel.
That's very good.

Now, get that right
to the back of your tongue.

Now, how was that?

Hold on. I feel like I'd better
have some, too.

This is the one I was dodging.

Particularly if you get
it at the back of your mouth -

it's very bad at the back
of your mouth. Yeah.

So, this is denatonium benzoate.

OK? It's intensely bitter.

It's probably the most bitter
molecule known.

And you can detect five molecules of
this in 100 million other molecules,

OK, in 100 million parts of water.

You have a huge number of bitter
receptors in your mouth.

Toxins are classically bitter.

Caffeine, quinine, lots of
medicines - very, very bitter.

So that's a line of defence,
the bitterness.

This is the fifth one. We've done
salt, sweet, sour, bitter.

Do you know the fifth one?
Er, umami.

Umami, amazing!

This is a Royal Institution
audience,

of course you knew it was umami!

Stick your tongue out and tell me
what this tastes of.

So this is monosodium glutamate,

and there are a few
different molecules

that can be put together to give
umami, which is savoury flavour.

Are you getting that?

Yeah, I'm getting a hint of savoury.

Yes. OK, now, look, let's mix
together a splash of all these.

Let's add a little bit
of bitterness. Not too much.

OK. Pour in some of that.

I'll add a bit of the salt.

A bit of sweet.

Pour in some umami.
Bit of sour here.

Now, have a swig of that,

and see what you make of that.

You're very up for this, Abel.

Is it nice?
No, it tastes like vinegar.

No. It just tastes sort of bad,
doesn't it? Yeah.

People think there are maybe
other tastes as well,

so there might be an oily taste.

You might be able to taste calcium.

You might be able to taste
some starches,

so other tastes may emerge,

but I can tell you what, Abel and I,
we could stand here all evening

fiddling around with this,

we would never make
anything delicious

because something crucial
is missing.

And I'm going to do an experiment
and show you what.

In the meantime,
big round of applause for Abel.

Great work.

So, we talk about delicious taste.

But actually, when we isolate
those tastes or mix them together,

it doesn't quite work.

Now, you have all been given
nose pegs, I believe.

Could you now put on your nose pegs?

Great work. Is it on tightly?

These are professional grade
nose pegs.

Now, the demo team are going to hand
out little beans to all of you.

They're going to pass them on,

so take just one bean and don't do
anything with it yet.

Just hold it in your hand,
pass them on as quick as you can.

And no-one's eating their bean yet.

And police the people around you!

OK, so everyone's got
their nose pegs on now.

OK. And I'm going to do
this with my fingers.

Keep your nose pegs on,

and take a breath,
put the bean in your mouth,

and chew, and...

Keep the nose pegs on.

You won't be tasting
much of anything.

When I say,
on the count of three,

you're going to take
the nose pegs off...

One, two, three!

...you will all just have
experienced a burst of flavour

and say the name of the fruit
you can taste together now.

Pear!

No! These are banana flavoured
jelly beans!

LAUGHTER

That was just underlining
Prue Leith's point earlier

that we eat with our eyes.

The point is, you all experienced
a burst of taste

when you took the nose pegs off,
didn't you?

There was a change in the room.

So, what was going on?

Taste, in simple scientific terms,

it's what happens in your mouth.

When you took the nose peg off,

what you experienced was flavour,

and flavour, that banana flavour
that you all thought was pear,

the banana flavour is smell.

But where exactly
are you smelling it?

Are molecules coming out
your mouth and going up your nose?

To show you, can we bring back on
Associate Professor of Public Health

at University College London,
and my twin brother, Dr Xand!

APPLAUSE

And you've really dressed
for dinner. OK, good.

Right. Well, we have a meal...
I'm getting a little hungry now.

We have a meal coming up. Great.

So, Xand is now...
Use the endoscope.

Xand's now going to show you a view

of the human body that
is extremely difficult to get

if you aren't the patient.

In order to understand

what we're looking at...

to show you the anatomy,
I have here a real human skull.

This is a skull from someone
who died more than 100 years ago.

They were a woman.

We don't know much else about them,

but skulls like this are
really, really important

for medical training.

So, Phil, can I... I'm going to come
and stand with my back to you

so I can show the screen.

And what we're having a look at here
is you can see the nose in the body.

Your nose doesn't go up.

It goes straight back
into your face.

Now, if I tilt the skull back
and you look right up the nose,

can you see up in there little holes

in the bone
at the very top of the nose?

Those holes are in
the cribriform plate,

and they are where the olfactory
nerves, the smelling nerves,

come through the bone
into the nose.

And that is where the molecules
from the banana-flavoured jelly bean

were getting to.

This is what Xand's
going to show you.

So I've now turned the skull around,
that's the back of the head.

And he's going to look here.

That's the nasal septum, the bone
that divides the nose in two.

Those holes go out the nostrils
and you can see the ridges of bone,

the turbinates inside.

So that's where we're going
to have a look now.

So he's now looking upwards,

and he's going to see... This is
really, really difficult to do.

We're going to see if we can get
a view of the back of the nose.

And there is a spectacular view.

This is the bone. The nasal septum
that divides the nose in two.

If you went out either of these
holes, you'd come out his nostrils.

There's a little nasal polyp there.

Many of you will have these polyps,
and they can cause problems.

Xand's already had one removed.

And just up here, that is
where those smell molecules

are going in order that
they integrate with your taste.

So, human smell is amazingly
sophisticated.

Humans can tell the difference
between five, maybe six different

tastes, but we can detect
the difference

between more than a trillion
different smells

and we're very good at it.

Xand, thanks for an amazing view
of the back of your nose.

Not...

Not easy to do that.

Now, just stay there, because...

Actually, get ready for the next
view.

Because by the time
that you've integrated

all the taste chemical
information from your mouth

with the resistance to chewing

from your jaw muscles,

the vibrations of crunch going
through the bones of your jaws,

with the smell,

you build up an incredibly complex
picture of everything

you put in your mouth,

and some scientists called
the whole thing flavour.

So there is even a debate in science

about whether we just mean,
when we say flavour,

do we mean the whole
package of experience,

or do we just mean the smell?

Now, what we want to now see
is we've arrived at the moment

of swallowing, and Xand is going to
now see if he can show us

a live swallow.

But to get this view,
he's going to go down his nostril.

Now, the entrance to the nostril's
also guarded by hairs there,

and Xand's going to very carefully
go directly back into his head.

OK? So he's going to get
to the back of his throat.

This is the path...
HE SNIFFS

...when you snort back snot, OK, this
is the path that snot follows.

So we're now going along
the base of his right nostril...

...and it's very difficult, this.

He's got to sort of
slightly push it...

We're now at the back of the throat.

That's a scar from when Xand
had his tonsils, his adenoids out.

And now Xand's going to look
down his throat,

and we're going
to see if we can get a view.

That's the back of the tongue,
the furry back of the tongue there.

And what we're looking at there,
we've got a beautiful view

of Xand's epiglottis there,

and we're looking down his windpipe,
his trachea,

and those V-shaped
folds of tissue there,

those are the vocal cords.
That's his larynx.

So, Xand, can you do a hum for us?

M-m-m-m. And you can see
he does a low hum.

Do a high scale. Do a high hum.
Mmm! That's nice.

XAND CHUCKLES

And when you laugh, your vocal
cords move in and out.

Now, most of the time, of course,
your vocal cords are apart.

You spend most of your life
breathing, not talking,

laughing or swallowing.

But the thing you can't see here

is the tube that the food
must go down.

It's folded flat,
and it's just back there.

It's behind the trachea.

And so when you swallow, the most
important thing is we don't get food

down into the lungs,

And that's what the epiglottis
is going to do.

Xand, thank you.
That was a brilliant demonstration.

APPLAUSE

Now, to understand
just how hazardous swallowing is,

I want to play a little game of
Operation Epiglottis.

What the demo team have built here

is a highly
anatomically accurate model

of Xand's oesophagus, trachea
and epiglottis.

So, this is Xand's mouth.

And you've got to imagine
Xand's throat here.

So, Xand's sitting on the stairs.

Xand's facing this way.

OK?

The trachea is in front
of the oesophagus.

So I need a volunteer to come and
play a game of Operation Epiglottis.

Er... Just here. Come on down.

APPLAUSE

Come on here. Now, what was your
name? Ethan. Ethan. Here you are.

Now, you are going to operate
Xand's epiglottis.

Do you want to have a go?
Just give it a pull. That's great.

So you can see, you pull it this
way, you block the trachea

and food can go down the oesophagus.

Release it, air can now go
down the trachea.

So we're going to play a game
with three levels.

Level one is just breathing and
swallowing the odd bit of saliva.

OK? So we're going to breathe,

so you want the air
to go down the trachea,

which it is doing very nicely.

OK?

And I might, once in a while,

I'll get you to swallow
a ball of saliva.

OK. So, are you ready?

You want to send the saliva
not into the lungs.

You ready, Ethan? OK, great.

And the saliva has gone
down into the stomach.

Beautiful job. And now we're
back to breathing.

That can go down there.

Now, Ethan, sometimes during a meal
we start doing...

We start breathing,
and talking and eating all at once.

And sometimes we start laughing
whilst we're eating and, um...

I've got to say, Ethan,
you're very good at this!

Hold on. Don't be too good at this!

So sometimes, Ethan,
we do a load of laughing

and we actually open our oesophagus.

Open our... Oh!

Ethan!

It is now game over, Ethan,

and it's going to be game over
for Dr Xand pretty soon

if we don't do something.

Ethan, what do you want to do
about the food

trapped just above Dr Xand's
vocal cords here?

Cough? Brilliant! Yes.
Could we have on...

Let's bring on the cough device
and see if we can make it cough.

Perfect. Now, Ethan, the cough
device is, it's fair to say,

a bit temperamental, so I'm going
to... Come and stand back.

Ready? Three, two, one...

Go! Whoa!

Very nice work. Ethan, bravo!

What a relief. Back to your seat.

Great job.

And if that hadn't worked,
we could have done some

abdominal thrusts
and moved to the next level.

But luckily, Ethan, you got
us out of the hole. Brilliant.

Brilliant work.

Now, Xand, we have prepared
a very, very, very

expensive, sophisticated
meal for you.

That is why I've dressed up.

I'm looking forward to it, Chris.

Is it lobster thermidor?

Is it lobster thermidor
with cheese and chocolate?

It's more expensive than that, actually.

This meal that we've prepared
for Xand

would be many, many hundreds
of pounds. Wow!

And it is, I would suggest,
the most sophisticated meal

you could possibly eat.

Xand, what we have prepared
is a capsule endoscope.

Oh, wow.
Now... Thank you very much.

In fact, I'll take the water.

Xand, show everyone what this is.

So these are...
Endoscopes we talked about

as those fibre optic cameras.

This is an endoscope that's just
a little capsule.

And it's incredible - it's got
a camera at both ends,

it's got a flashing light source,
as you can see.

It's got a battery inside it,
and it has a radio transmitter.

So, when Xand eats it, we will get
images from inside his body.

Swallows it, not eats it.
Swallows it, yes.

That's true. You shouldn't eat them.

Yes. Don't chew it!

OK... Xand, have a big, big
gulp of water.

What you are now going to see
is what we pre-recorded.

Now, the pill is in your stomach.

The pill endoscope. Yeah.

Now, Xand, how did that pill
get into your stomach?

Did it just fall down
by the force of gravity?

Well, yes... No, it didn't!
You know this, you're a doctor.

OK, so my oesophagus
is smooth muscle,

and those rings of smooth
muscles squeezed it down

through a process
called peristalsis.

So it got pushed... Very good.

Right, so it squeezed
down there deliberately,

and that means that we can eat in
all kinds of situations, can't we?

In space, upside down,

and that is why, Xand, for the
next course of your meal,

I'm going to invite you to
a very fine dining establishment

with some quirks.
Come with me, Xand.

AIR HISSES

Xand, welcome
to the Wheel of Doom!

What?! Why's it called
The Wheel of Doom?

I mean, it's the
oesophageal inversion device.

I must stop calling it that.

Now, stand on the Wheel of... on the
oesophageal inversion device

and strap yourself in.

Great. Now, Xand, for the second
course of your meal,

we're going to turn you upside down,

and get you to drink some cream.
Are you ready?

Invert the oesophagus!

Here he goes. Whoa!

Great work. OK. Now you're upside
down, how are you feeling?

OK. Not nice, is it?

Now, have a big gulp of cream.

Are you swallowing it?

The cream is not pouring
out your eyes,

your nose or your mouth. No, I
thought it would, but it hasn't.

Brilliant. OK, let's flip
him the right way up.

And that has worked
spectacularly well.

You can see, not only is the food
squeezed down the oesophagus

or up the oesophagus
in this case very actively,

but there are valves along the way
that keep it in place.

Xand, brilliant work.

And I guess the team... Can you just
spin him round again

and get them to finish the meal?
Wait, no!

Chris! Good luck, we'll see you
later on. I'm still on the wheel!

No! Chris! Thank you.

I'm keeping turning!

To better understand the stomach,

which is where that pill is now,

I want you to welcome
a very special guest.

She is an anatomist.

In fact, she's one of the authors
of the current edition

of the famous medical textbook
Grey's Anatomy.

She's our official anatomist
on Operation Ouch.

And there is no-one better to
explain

to us stomach anatomy and function
that I can think of.

Welcome, please,
Professor Claire Smith.

APPLAUSE

Hiya! Ah!

Hi, Chris. Claire, you've brought
some stuff with you, haven't you?

I have. So, I've brought
with me a pig's stomach.

OK, so this is a pig stomach
that we're going to look at,

and what's important is we have to
say this is not for the squeamish.

Actually, on three,
can we all do a gross alert?

Are you ready? Everyone just shout,
"Gross alert!"

One, two, three!

Gross alert!

So, if you don't like looking at
bits of anatomy, then look away now.

OK. Claire, show us.

So, by a quirk of nature,

human stomachs and pig stomachs
are very similar.

But pig stomachs are quite
a bit bigger than ours.

And it's folded in the same way,
so it's in a C shape.

OK. Can we pick it? Yeah!

Pick it up. That's the oesophagus.
That's the oesophagus.

Yep, and it goes into an area
really close to the heart.

So the stomach, when we talk about
stomachs we often think

about, we sort of talk about the
stomach and we mean the abdomen.

The stomach, the organ,
is near the heart.

Yeah, so it's sitting
just underneath your lower ribs.

So, just about here, and heading
towards the middle of the body.

And it's got this dome shape
on the top,

called the fundus,
and this is where air sits.

So this is where burps come from.

It's the burp factory. Yeah.

It's the burp factory.
I love that. The fundus.

OK, there you go.
It was not me, it was my fundus.

Then we have the main body of the
stomach,

and this is where the process of
digestion is going to be happening.

And then it leads
into the gatekeeper of the stomach,

the pylorus,

which controls food going from the
stomach into the small intestines.

And that's a sphincter.

Yes. A ring of muscle. Yeah.

And that can clamp down tight,
so the stomach can be a sort of

sealed container. Yeah. OK.

What is the function of the stomach?

Why don't we just have a tube
going all the way through?

So, it's more than just a bag.

It's got a special arrangement
of muscle.

Throughout the rest of the tube,
you've got circular muscle

and longitudinal muscle, which
helps push the food along.

And in the stomach you've got
this extra oblique layer,

and that helps with the mixing.

And I'm going to cut
into it and have a look.

So do look away
now if you are squeamish.

And all of the fibres of muscle
run in different directions.

And that really helps with
the mixing of the contents.

What we're going to see now...

Just extend that down a little bit.

...is the lining of the stomach

is thrown into lots of folds,

and these folds are called rugae.

And if I turn the stomach inside
out a little bit... Oh, wow.

...we can see those rugae
really beautifully.

And they're there to help
increase the surface area.

If we were to zoom in lots and lots
onto the cells that we can see here,

we would see cells
that are making acid,

we would see cells
that are making enzymes,

some that are making hormones,

and some that are creating
this mucus.

So the stomach is storing food,

and I always think of it
as like cleaning food

with the fairly strong acid
that's in there. Yeah.

Does it have any connections
to the rest of the body?

Is it more intelligent than just
a sort of muscular bag?

It is, and I thought
you might ask that,

so I've got another stomach.

Here we go.

I'm going to empty that one.

So, our stomach
holds about 1.5 litres,

and it can be stretched more to be
about three to four litres.

So I've already made
some vegetable soup,

and I have already filled that
into our stomach.

OK. If we want to lift
the stomach out,

we can see how big
and how filled it is.

So if you want to hold that there,
and I'm going to release the clamps.

Brilliant.

And let's lift it up nice and high.

So it is really, really stretched.
Amazing!

So we've got huge capacity. Yeah.

Um... So this is now filled
with far more vegetable soup

than any of us would ever drink.

What happens when you put
this amount of food or fluid

in the stomach?

If we have a look on the surface
of the stomach,

we can see these white and
sometimes red wiggly lines.

And these are the arteries, veins
and nerves that supply the stomach.

And one of the key things
is these nerves are communicating

from our brain, and back up as well.

So these are branches of a nerve
called the vagus nerve,

which starts in the brain,

goes through our neck,

through our thorax,

and then goes to our stomach
to tell our stomach

to start those muscles
moving and mixing.

But when it gets really full,

this nerve also says
back up to the brain,

"I'm getting quite full. Please
don't..."

So, the vagus nerve...

Those of you doing biology,
or if you become health care

professionals, it's one
of those sort of key nerves

in the body that
you have to learn about. Yeah.

OK. And amazing to see it
shown there.

Claire, that's an incredible
demonstration. Thank you so much.

Big round of applause
for Professor Claire Smith.

So it will then be time
for food to leave the stomach,

and, Claire, remind me,
where are we heading to next?

The food will now go into
the duodenum,

which is part of the
small intestine.

The small intestine. It's not that
small! That's how I remember it.

The large intestine is very wide.

Small intestine, very, very long.

And I'm going to show you
where it is here...

Now, this is a perfect scale model
of my gastrointestinal tract.

You can see my lungs, trachea here.

And I will pull out my oesophagus,
my stomach.

Let's pull the colon off.

We're going to leave
the pancreas behind.

The liver's there and we're going
to pull off my small intestine.

Now, Claire, do you mind
just holding the oesophagus? Yep.

In fact, give it to a young... maybe
a young person there. Yep.

And I'm going
to go across here,

and I'm going to pass
this back to you.

Do you mind holding the...?

This is not the nicest bit!

LAUGHTER

I'm not going to say it.

Hold the distal end of the colon.

There we go. Beautiful work.

And what you can see here,
this pink tube, starting at

the pyloric sphincter and going all
the way to the ileocecal junction,

where it goes into the colon,
the large intestine,

this is the small intestine.

It's five metres of our
seven-metre journey tonight.

And the mechanical bit
of digestion is done now.

What's going to happen in here
is chemical digestion.

Powerful enzymes secreted
by the gut and by the pancreas

are released into here,

and they start chemically
breaking down the food,

into its individual molecules
that can then be absorbed.

And why is it so long, do you think?

What's important? Who thinks
they know why is it so long?

What do you think,
in the Christmas jumper?

Um, I think that, because, like,
it needs to make sure

that all of the substances
are properly processed

and that they get all of
the nutrients from them.

Very good, I love that.

So everything's properly processed
and you get all your nutrients.

It's long cos it needs
to have a big surface area

to absorb those nutrients.
Brilliant answer.

Let me show you what the actual
surface area of the small intestine

really is, because it's more than
50 square metres.

So the back row
have an exact scale model

of the true internal surface area of
this small intestine,

and you can see it's enormous.

It's as if this tube, instead of
having a three-centimetre diameter,

had a ten-metre diameter.

So the big question is,

how do we get that much surface area

into a tube with this small
a diameter?

And the answer,
we are about to reveal,

Claire, can you say the word for us?

What do we call them?

Microvilli! The microvilli -
the finger-like projections.

And Dan, if you're ready to
whip away... Take it away now!

So, tiny finger-like projections
in here.

Far too small to be seen
with the naked eye.

These increase the surface area
and allow you to absorb

all the breakdown products
after your enzymes

have gone to work on food.

Brilliant!

Brilliant work, all of you there
with your pink gloves on.

And it's really important,
like the stomach, you saw,

there's a rich set of nerves
connecting the stomach

back to the brain,
sending signals back.

The same is even more true
of the small intestine.

It's sending information
back to your brain

about the nutrients
that were in the food,

so that you can then link that
smell, the experience in your mouth,

with the actual reward
you get from the food.

Did it contain lots of useful
sugars and fats and proteins?

So information goes back and it also
says when you've had enough to eat.

So fullness signals
come from the small bowel.

It's part of that sensory apparatus

that helps you learn which foods
you are disgusted by,

and which foods you desire.

And by the time we get down here,
almost all of the nutrients in food

have been absorbed.

The only thing you can't digest
is the fibre in your food.

And it's left here
in a liquid slurry.

There's hardly any nutrition
left in it.

It's just the fibre
and a few digestive juices,

and it's going to go into the colon.

And here is the weird thing
about fibre.

As I say, we all know
that fibre is good for us.

Yes, we're constantly told
to eat fibre.

You don't produce an enzyme...

Your bodies don't make an enzyme
that can digest it.

So, in order to make use of it,

we have to employ a few friends
to give us a help.

And those friends are some bugs
that live in this bit of the colon.

And In order to understand...
I'll take that back from you.

In order to understand
just how those bugs work,

I want to welcome an expert in
our internal microbiome,

an expert in microbiology -

she's a medical doctor
and an incredibly eminent scientist.

Please welcome
Professor Louise Kenny!

APPLAUSE

Hi, Louise. Hello, Chris.

I thought for a second
you had turned into a goat.

You've brought a goat with you?
I have. What's the goat's name?

The goat is called Juniper.

Juniper. Hi, Juniper.

What are you up to? Do you want a
scritch behind the ears?

Well, let's give her a little bit of
beet. Do you want a beet? Hey...

There we go.
GOAT BLEATS

There you go.

Do you want that?

I think she might want... No!

Juniper! Juniper!
Hold on, hold on.

Have a bit of... Have a bit of beet
leaf. There you go.

There you go. How are you doing?

How are you doing?

So, why have you brought a goat,
Louise?

Well, goats are really interesting.

They've got a very different
digestive system to humans.

And they demonstrate the importance
of something called

the microbiome perfectly.

So you can see that juniper
is eating lots of plants. Right.

Goats have a completely
plant-based diet.

Juniper, look up here.
We've got a picture

of your gastrointestinal tract.

I don't think Juniper is interested
in her gastrointestinal tract!

Oh, Juniper!

Does Juniper's handler
want to come out?

Can we get your name?

Jenny. Hi, Jenny.

How are you doing?

So, Juniper... Only eats plants.

...makes a living out of eating
all of that fibre

that we're told we need
to eat constantly. Yup.

Talk me through her guts,
compared to ours.

So, they're known as ruminants,
because how they eat

is that they eat, um,
cellulose-based plants.

They swallow them into the
first part of their stomach

and then regurgitate it.
It's called chewing the cud.

And they do that lots of times
to help break up the cellulose.

So more mechanical breakdown
of food. Exactly, yes.

And you can see Juniper
doing that right now.

She's sort of munching away
on those greens.

She will swallow it down...

So she swallows it down, and it goes
into this part of her stomach.

So you can see
that her foregut is huge.

And we've heard, many of us,
that cows have four stomachs.

Is that also the case with Juniper?

So Juniper has four components
to her stomach,

including this really important one,
the rumen,

which is where they get
their name "ruminants".

So she'll swallow the cellulose,

and within this
big fermentation chamber

are literally trillions
and trillions of microbiota.

So, bacteria, fungus and viruses

sitting in this fermentation chamber
ready to break down the cellulose.

So, do goats...

I guess most of us would assume
that herbivores make an enzyme

to break down cellulose, in the
same way we make enzymes

that break down proteins
and fats and carbohydrates?

That's the key difference.
They don't. They don't?

Most of their digestion occurs
because of these microbiota.

Without them, they would not be able
to break down their food

and they'd actually die
of starvation. Really?

And how much of their calories can a
goat get from the fibre in plants?

About 70% to 80% of their energy
comes from the microbiota

digesting the cellulose in plants.

Right, they'll also get a bit of
energy from some protein and fat

in the plants, but it's mainly
the bugs digesting the cellulose.

The cellulose, exactly.
Amazing.

So, just like us,
they can't do it...

How much energy can we get
from plants by contrast?

Well, a typical adult human
on a typical varied diet

would get about 10%.

So it's a huge difference.
OK.

So, the bugs are doing the same
basic function in Juniper and us.

Exactly. Just helping digest
the food.

It's just that in ruminants
they're mainly in the foregut,

and in humans,
they're mainly in the colon. OK.

And what then did
the bugs do for Juniper?

So, when the bugs eat the fibre,
what then happens?

Well, they break the cellulose
down into far more simpler compounds

that Juniper can then absorb
and extract energy from.

OK. So without that,
she wouldn't be able to extract

energy from her food, and she'd
be a very, very thin goat.

And she's definitely not.
She's not a thin goat.

She seems to be happy.
Is Juniper happy? Yes.

OK, good.

Goats and humans - do we have
a similar microbiome?

We do.

But your microbiome changes
over the course of your life.

And even over the course of the day,
it's far from static.

Really? What kind of things
change it?

It's a really dynamic environment,

and it's changed
mainly by the environment,

and most particularly of all, food.

Your diet is the most... by far and
away the most influential factor

in determining your microbiome.

The soil, if you like, we put in
that the bugs grow on. Yup.

The food that we eat.

Every gram of food has literally
millions of bacteria within it.

OK. That's amazing.

I think we could do a very quiet
round of applause for Juniper.

We don't want to scare her.

And for Juniper's helper,
thank you so much.

OK. You've got another demo here,
Louise. Talk us through this.

I have. So we were talking about
the difference between

microbiome in goats and in humans.

So these two tubes represent
the microbiome of a human

here on the left,
and a goat here on the right,

and you can see
that they're really different.

Instantly, you can see
that the microbiome of a goat

is far more copious and diverse
than it is in the human.

They've got more bugs
and different bugs.

Exactly. There are about 11,000
species of microbiota

in the gut microbiome.
Is it just bacteria?

No, it's predominantly bacteria,

but it also includes things
like fungi and viruses.

Whereas in the human microbiome,
we're far less diverse,

so far we've counted about
3,000 types of bacteria.

But there are these commonalities,
the blue bugs and the yellow bugs,

in this model. Yes.

So in humans,
about 90% of our microbiome

is made up of just
two species of bacteria -

bacteria called
Firmicutes and Bacteroides.

And you can see that exactly
the same bacteria exist in goats.

You'd also find them in other
mammals as well.

But then you have this big bunch
of things that we don't have.

And within this
bunch of the microbiome

are the critical bacteria
that help break down the cellulose.

Do all humans
have a similar microbiome,

if we got the bugs
out of everyone in the room?

No, it's really diverse,
even within species.

So there are some similarities.

But your microbiome changes
over the course of the day

and it changes drastically
over the course of your life.

It's very simple at birth,
and then it becomes

very complex as you grow up.

And then there's some evidence
that towards the end of life

it becomes very simple again.

But it's always changing.

It's a constantly evolving
environment.

I've got an identical twin brother,

and you will all know,

identical twins are
genetically the same person.

We come from a single sperm
and a single egg.

Here we are.

Now, I'm guessing
at this stage of our life,

when we used to poo together,

we did share
quite a bit of our microbiome.

Probably, because not only
are you pooing together,

but you're living
in very close proximity,

and you're almost
certainly sharing meals.

You will be eating exactly the same
thing in the same environment.

So your microbiome at this
stage is likely very similar.

And these days, while Xand
and I have the same microbiome,

we haven't lived together
for 20 years.

Despite the fact that you're
genetically identical,

there's no chance that your
microbiome will be the same any more

because you don't live
in the same house,

you don't share the same meals.

Your microbiome will look
far more like your partner's

and your children, even your pets.

Really?

So my kids I get, because my...

I think I can say -
they're not here -

but I think even my kids would
admit children, broadly,

younger than you, are not always
the most hygienic. No.

I mean, I know I swap
microbiome with my kids,

cos once every six months
I get worm infections from them.

So, we must be eating
a certain amount of faeces.

So, I get it with the kids,
but what about the pets?

Well, do you have a dog? No, we're
a cat family through and through.

Here we go.
This is my cat, Winston.

A long-haired moggie.

It's a very handsome cat.

It's very likely
that you and Winston

have a co-dependent microbiome.

You probably share elements
of your microbiome with Winston.

So that I don't understand,

because cats kind of keep
themselves to themselves.

My cat is not sleeping in bed
with me. It doesn't...

It's not like a dog.
It's not licking my face.

What else does it lick, though?

Well, it licks... It spends a lot of
time licking its own bum. Yes.

And does it lick anything else?

Well, I think we do have
a video of Winston.

This... Winston really likes...

Winston will only drink
from the kitchen tap.

So now Louise is
kind of pointing this out,

I'm guessing it is possible
that some bum bugs...

It's not possible,
it's almost a certainty.

So if Winston was licking his bum
and then has licked your tap,

and then you've had a glass
of water,

you will have bugs that have
come from Winston's bum.

I'm going to get a second...
I'm going to get a second tap.

I mean, looking at this tap, it's
not the cleanest tap anyway, is it?

No! I think we're going to become
a dog family from now on.

And is that a bad thing, sharing
a few bugs with our pets?

No, not at all.

There's a lot of evidence
that if you have pets,

you have a much more diverse
microbiome,

and everything we know about the
microbiome,

and we're still learning - there's
still so much to this science

we don't understand,

but what we do think is that
a very diverse microbiome

is associated with robust health.

If you want to keep
your microbiome healthy,

you just need to have
a healthy diet.

So, lots of fresh fruit
and vegetables,

whether they're cooked or raw.

Things like whole grains,
pulses, lentils.

A nice, varied diet will result
in a really varied microbiome.

No need for any fancy tests.

And anyway, there's a very simple,
cheap and readily available way

to tell whether your microbiome
is healthy.

FARTING

Excuse me! Is farting
a sign of good gut health?

Absolutely.

Farts are normal,
and they're very healthy.

OK. I'm absolutely delighted
to hear that!

Big round of applause
for Louise Kenny.

So, farts tell us a little bit
about our bowel health,

but it's also really important
to look at our poo,

because our poo can tell us a lot
about how healthy we are.

And it is worth glancing at it
once in a while,

and to have a look at
some more solid evidence,

it is time to call on
the variable poo machine.

Big round of applause!

APPLAUSE

Now, obviously I'm going to need
a volunteer to run the poo machine.

Everyone wants to run
the poo machine!

Now, I feel...
Now you, with the snow top...

The grey top with the snowman
on it.

You were very quick with your hand.

A big round of applause.

What's your name?

Ejay. Ejay. Yes.

Great to meet you, Ejay.

So, what we have here
is four model colons.

Now, do you know what the main
function of your colon is?

It's got two functions.

It's the home of your microbiome -

the bugs we've been talking
about with Louise.

So they digest the fibre,

but it also absorbs water
from your poo.

So we're going to make three
different poos here.

You're really wishing you hadn't
had that hand up so quickly!

So what we've got now...
What are the elements...?

First of all, Ejay
is going to make a healthy poo.

OK? So what are the two things we
need for a really healthy poo?

Vegetables? Vegetables! Great.

So, fibre - fresh fruit,
vegetables, pulses.

Things like lentils.

Really good stuff.

So, this is what we've got -
some fibre in this bowl.

And I want you to pour some water...

Let's add a bit more fibre
to the bowl.

Great stuff. A bit more fibre.
Great.

And then we're going to pour
in quite a bit of water.

Pour in that thing of water.

And what I want you to do, Ejay,
is to mould a nice poo shape

out of the fibre.

Great stuff.

Now, this is what would be
happening in your gut.

The fibre is all
that's left in your colon,

and what would happen in your colon

is the gut would absorb the water

so you're left with a moist,
but fairly firm,

sausage at the end of the gut.

So you're going to sit
down on the toilet,

it's going to make
its way into the rectum,

and you can see how easy this is
to pass into the toilet below.

Are you ready?

OK, just go. And it passes easily.

You relax,
and it goes into the toilet.

Now, if you don't eat lots of fibre,

OK, what arrives at the rectum,

which is the storage bit at the end
of your gut, is more like this.

OK? It's just a dried out
clump of bugs,

so you can mould that a little bit.

There might be a little bit
of fibre in it,

and if you don't drink enough water,
it will end up being really dry.

The colon will suck all the water
out of it.

So these are the elements
for a healthy, easy to pass poo.

Fibre and water is important,

and what we're going to see here...

So, Ejay, let's come along here

and see if you can get it
to go down into the toilet.

Now, we may have to give
it a bit of a hand.

Can everyone go...

Remember when you were very little
and you'd get constipated?

Can everyone, on the count of three,
strain together?

One, two, three... U-h-h-h-h!

EVERYONE STRAINS

LAUGHTER
It's really... Hold on.

Sometimes in hospital you do have
to give people a hand with this.

So, there we go.

You can eventually push it out,

but poos should obviously not
be this hard to push out,

and if you pass lots of dry, hard
poos like this,

it can damage the lining
of the anus.

You can get fissures, haemorrhoids.

You can ask your grown-ups about
these things after the lectures.

Almost all grown-ups have experience
of these things.

So, fibre and water - really
important for having an easy poo.

You shouldn't have to do
all that straining and pushing.

So, brilliant work.

We've had a healthy poo,
a constipated poo.

Now time for some diarrhoea.

Are you ready?

So, diarrhoea.

Maybe we've eaten some fibre, maybe
we haven't. It doesn't matter.

Pour the water into there
and bring it over here.

The bugs... There are lots of things
that cause diarrhoea,

but the common bugs that do it

either stop your colon
absorbing water,

or sometimes they actually
make your colon produce water,

and so they make your poo,
your stool, really, really runny.

So, this would be
a bacteria like cholera.

Cholera makes water go
into your stool,

and it can be really,
really dangerous,

cos you dehydrate very quickly.

So pour the cholera poo
through there.

And, in this case, of course,

Ejay, we didn't even make it
to the toilet.

LAUGHTER

We've all been there.

A close call,

but great, great work.

So, Ejay, you've been
a brilliant sport.

Thank you so much for demonstrating.

There is a final scenario
I want to demonstrate.

You will remember that what should
arrive at the beginning of the colon

from the small intestine
should really just be your fibre.

Almost all of the protein
and the fat and the sugar,

the nutrients, have been absorbed
into the body.

So the fibre goes in there.

But there are some infections
which damage the villi,

the finger-like projections
in the small intestine,

infections like giardiasis.

When those villi go away,
the surface area shrinks

and you're left not being able
to absorb your sugar, salt

and protein, so they go into
the large bowel

and, Louise, what then happens
when it gets into the colon, Louise?

Well, the bacteria in the colon
don't normally see sugar and fat,

and when they do,
really bad things happen.

Really? OK. Very bad.

And they're quite good
at eating that stuff.

It's an easier meal for them.

Oh, they absolutely love it,

but it has some quite disastrous
consequences for the host.

So what I'm going to do now
in our final colon

is put in a little bit of sugar
and fat and protein into this gut,

because the villi here
have been flattened,

and this gut is malabsorbing -
it hasn't absorbed them.

So we're going to see what happens.

Are you ready? OK...

GROANING

Oh!

GASPS AND CHATTER

There we go!

Yep.

And that...

And that, and Louise
will confirm this,

that is why we call conditions
like giardiasis

"two bucket diseases",

cos you need a bucket
at both ends to deal with them.

Norovirus is another one.

Now, that poo that you get when
you're not absorbing your nutrients,

it's foul and it floats,

because it's full of fat,

and a healthy poo contains almost
no real nutrients at all.

Your gut, your digestive tract,

is incredibly good at absorbing
everything you need from your food.

And what happens to those
nutrients, their destiny,

that is the subject
of my next lecture.

Thank you very much!

CHEERING AND APPLAUSE