Guts: The Strange and Mysterious World of the Human Stomach

The Science Museum in London

is being prepared for a most peculiar event.

Here, live, in front of hundreds of people,

an alien world is about to be explored.

-Urgh, God!

-SQUELCHING

Keep going and keep going...

'It will be scrutinised

'and probed.'

PEOPLE WINCE

Our guts.

A mysterious organ.

Writhing tubes,

corrosive acid

and home to its own unique ecosystem.

Mmm!

'Its dirty work, normally invisible,

'is about to be laid bare in all its gruesome detail.'

Oh, God! That is horrible.

'And the guinea pig for this?

'Well, that'll be me.'

During my medical training

and more recently, as a television presenter,

I have taken part in some pretty bizarre and painful experiments,

but nothing quite like this.

'There's a new attraction at the Science Museum today.

'My stomach is going on display

'to be experimented on.

'I want to explore just how strange our digestive system is.

'Outside our conscious control,

'what's going on in this unfamiliar, weird world?

'Guiding me through is gut expert Dr Mark McAlindon.'

-Hi, Mark.

-Hi, Michael. Nice to meet you.

-And you.

-It's a very theatrical setting, isn't it?

-It is.

It's not a conventional medical environment, but there we go.

-I think we'll have some fun today.

-I think so too.

-Right, so what happens next?

-OK,

-so first of all, stick this one in.

-Ooh, cold.

'Mark is going to monitor me as I eat a typical day's food.

'And we'll all watch what happens as it goes on its merry way.'

These lucky visitors

will see parts of me that have never been seen before.

-Perhaps I could ask you to put that over your head.

-Sure.

'We're using the very latest technology,

'a miniature camera inside a pill.'

It will, hopefully, travel through me

and transmit live pictures from the depths of my guts.

'And as it goes, I'm going to take part in a number of tests.

'It's a leap into the unknown.

'We'll be trying things today that few have tried before.'

Lie down, we'll just do your pulse and blood pressure.

Ooh, elegant chaise longue here.

There is one, which is just as well,

which means you're as fit as a fiddle, fit to go.

Marvellous. Fit to swallow pills.

Once swallowed, I'll have no control of the camera.

The murky world of my intestines is a law unto itself

and how long it will take the camera to work its way through

is anybody's guess.

Um...

-Um...

-Hmm...

-Uh...

16 hours.

-30 hours?

-Two days?

-Depends what you've eaten, really, doesn't it?

-24 hours?

-12 hours.

-A few days.

-One day.

-Two days?

Two hours?

Food can take up to three days to travel through the gut,

but last night, I drank four litres of laxative to clear the way,

so I'm expecting my camera to travel rather more quickly than that.

OK, Michael, well, I'd give you the pill camera.

And if you'd like to take it out of its holder,

-if I can actually manage that.

-Right, OK.

'This pill houses a mini film crew,

'complete with lights and camera.

'It will take pictures three times a second

'and transmit them to screens here in the Science Museum

'via sensors on my body.'

-So, Michael, ready when you are.

-OK.

Pop that into your mouth, a few gentle sips of water.

-Ah! That's it...

-That's it gone?

It's gone! It's gone on its long journey.

I can't get it back, it's too late.

'My first feeling is one of relief.

'The camera is clearly working

'as it slides down the back of my throat

'and heads towards my stomach.'

It's very funny!

HE LAUGHS

Propelling the camera down

are powerful muscles that lie in my gullet or oesophagus.

Any time you swallow food,

the oesophagus will be able to tell that there's a force on its wall

and that initiates the process of contraction of the muscle

to try and push it further down.

It's really quite magical.

So this black hole here,

soon you'll see the capsule passing into the stomach.

-Here it goes.

-Ooh, there it goes.

Down here, it's a cavernous, alien landscape.

And you can see some white blobs of porridge I ate for breakfast.

But what's really striking

is there is so much pulsing and throbbing movement going on.

It's something we're normally completely unaware of

but it's happening all the time and throughout our digestive system.

Our guts are a tireless machine

and I spent a morning in the run-up to this exhibition

having some scans to find out

just how the different parts work together.

I've seen my heart beating...

my brain buzzing...

but I have never seen my guts in action.

Well, lucky me. Today, I get that chance.

Here at University College Hospital,

radiologist Stuart Taylor and his team

are using a stop-motion technique

to capture the unconscious movement

involved in a journey through our guts.

'To get the best-possible images,

'I'm knocking back a rather disgusting drink.'

This liquid's got a special sugar in which isn't absorbed by your body,

so when we do the scan, I'll be able to see

the inside of the bowel very well and how the bowel works and moves.

-It's an acquired taste!

-It is, probably not something

you'd to choose drink every day, but hopefully not too bad.

Michael, I'm going to start a few scans now, OK?

Breathe in. And hold your breath.

As I hold my breath, the team takes a series of high-speed images.

This is the last scan.

These will be stitched together

to form a 20-second film of my guts in action.

All finished. Well done.

'This technique is normally used

'to diagnose disorders affecting movement in the gut.'

That's absolutely fascinating.

What surprises me is just how much movement there is in here.

It really is a dance.

I was lying completely still in the scanner,

but this slice through my guts shows they were anything but.

Any food passing through my digestive system

takes the same route,

through this pulsating, writhing, continuous tube...

Down my gullet and into my stomach,

then into my small intestine, or small bowel.

Next stop, it's the large intestine,

otherwise known as the colon.

And then it's out the other end.

It's this constant movement throughout our guts

that enables our bodies to transform food

into the nutrients that keep us alive.

'Back here at the Science Museum,

'the camera has travelled down my gullet and into my stomach,

'where it's transmitting live pictures to an enthralled audience.

'Now it's time for some food to start its journey through my guts.

'And Mark's got something else to view it with.'

The pill camera is still down in my stomach

but we're about to stick another camera in,

which is slightly intimidating-looking.

It's got a nice...tip there and it's going to go down through my nose,

which should be fairly unpleasant

and when it's down there, we'll get a much better look at the stomach

and then I get to eat a little bit,

so we can sort of see more of the stomach action.

-This is going to be a bit uncomfortable, isn't it?

-Little bit.

Urgh, God! Brings tears to your eyes.

-Ooh, that is uncomfortable.

-There we go, there we go.

-Oh, dear.

Although this camera will only go as far as my stomach,

it is steerable and should give higher-resolution pictures.

Oh, that was so uncomfortable!

And there we are into the stomach.

And there's some porridge from earlier.

-You OK, Michael?

-Yes.

Ah. Thank you.

The food has arrived.

Chicken noodle soup and brightly-coloured veg,

so we can pick them out when they're inside.

-I know it's not the perfect position for dining.

-No, I can't even see it.

But would you like to try a little bit of something?

How about if we go for something with colour?

OK, something red?

That sounds good. A few bits.

-A few bits of yellow?

-Yep.

So we should see it passing by in a minute.

-Ah, there we go.

-Yep, something green went past.

There might be a little bit of chicken.

-Oh, there we go. It's coming now.

-There it is.

You can see the way the food is being churned up

by muscles in my stomach wall.

As well as this mashing action,

my stomach is also releasing gastric juices

and began doing so long before I started eating.

Gastric juices are released

at the sight, smell or even thought of food

and the powerful chemicals they contain

will help turn these lumps of food into a creamy mush known as chyme.

Oh, nice.

But I don't think I can bear having this camera down here any longer.

Coming back.

Oh, that's horrible!

-Back of your nose.

-Oh, horrible, horrible, horrible.

Oh, God! Bloody hell.

That was horrible. Ah!

MICHAEL GROANS

To see my food sloshing around in my gastric juices

was a novel experience.

But it wasn't a camera that gave us the first insights

into the workings of the stomach.

It was actually a gunshot wound

that revolutionised our understanding of human digestion.

Our story starts in June, 1822,

when a young man is accidentally shot in the chest.

GUNSHOT ECHOES

The victim was Canadian boatman Alexis St Martin,

working on the shores of Lake Michigan.

The blast ripped through his ribs,

his lungs and the front wall of his stomach.

First on the scene was young army doctor William Beaumont.

He dressed the wound, but really didn't expect his patient to live.

'But survive he did,

'and I've come to meet medical historian Lindsey Fitzharris

'to find out how this unfortunate accident

'went on to lay the foundations of modern gastroenterology.'

-Hi.

-Hi, Lindsey.

So this is an actual diagram of the original wound

and you can see the outline of it. It was really big.

When St Martin was shot,

it was about the size of a man's palm, essentially.

-Wow. That big?

-Very big, yes.

It was on the left side of the chest, right about there.

We tend to think of the stomach being low

but it's actually much higher up, right below the diaphragm.

When he was shot, parts of his undigested breakfast

began pouring out, along with bits and pieces of his torn stomach,

but Beaumont's called to the scene

and over a course of a year, he's able to nurse Alexis back to health

and what happens to this giant hole is that it shrinks

and it forms this 2.5-centimetre-diameter fistula.

Right, so you've got the original hole, size of my palm,

-and it's shrunk right down.

-Yes.

-But it's still open?

-It's still open

and through that fistula, he can see directly into the stomach.

It was an incredible opportunity

for Beaumont to study the living digestive system in a way

that no other surgeon or physician had been able to do until that point.

Beaumont certainly made the most of this opportunity.

Once his patient had recovered,

he employed him as a handyman

and studied his stomach for the next ten years.

He subjects St Martin to a series of experiments.

And he takes little bags like this

and he wraps pieces of food in these bags,

cabbage, meat, all kinds of things,

and he sticks it directly into that fistula.

Very nice. So he just pops it into this convenient hole?

-Pops it into the stomach, yes.

-Leaves it there to brew for a while?

-Exactly.

-Like a cup of tea, and then brings it out, inspects it.

He was very interested

in how different conditions affected the digestive system -

for instance, if it was cloudy, if it was sunny, if it was cold.

As well as putting things into St Martin's stomach,

Beaumont also sucked out the juices that were produced there.

And it was these previously-inaccessible bodily fluids

that were to turn popular beliefs about digestion on their head.

Did he know what that juice was?

He didn't at first, but he had it analysed

and they discovered, of course, what we know today,

that a lot of it is hydrochloric acid, which is highly corrosive.

As well as acid, the juices contained digestive enzymes

and Beaumont discovered he could break down food outside the body

simply by mixing it with this juice.

Until then, it was widely believed

that digestion was purely mechanical.

But Beaumont showed that the gastric juices

also had a vital role to play.

This was a big revelation, presumably?

Oh, it was a huge paradigm shift.

I mean, you're going from the mechanical view to the chemical view

and he was criticised for it back home in America.

He really achieves his fame afterwards, and today, of course,

he is known as the father of gastric physiology.

This is a wonderful story, an extraordinary story.

It is an extraordinary story

and one that really changed how we understand the body today.

Here at the Science Museum,

I want to demonstrate the power of gastric juices.

Now we made up a solution here,

which contains the right balance of acid and also enzymes

you would find in typical stomach secretions.

Now, let's check the pH of this one.

A neutral solution is pH 7.

Anything less is considered acidic.

I'm guessing it's going to be around 2.

I'm expecting something quite acid.

-Ooh, right. Really incredibly red, isn't it?

-Very much so.

-So that's a 1?

-It's a 1, so...

-Battery acid?

Battery acid it would be, absolutely, it's really quite powerful.

In fact, powerful enough to kill most harmful bacteria

that might come down into your stomach with your food.

And take a look at this.

One of the tests I've always wanted to do,

I read about this when I was a kid,

was that if you could drop a coin down into your stomach,

it would kind of clean it.

Let's try it and see.

What I'm surprised by

is just how robust the lining of your stomach has got to be

because it's got to put up with acid with a pH of 1.

Yeah, well, there's a millimetre thick mucus all round the stomach,

in which there are bicarbonate ions

which keep it slightly more alkaline,

so it protects the stomach lining

from damage from the gastric acid.

Right. Let's have a look.

Ooh, yes! Cool!

I think we see a clear change there.

So, clearly, the degree of acidity,

the hydrochloric acid has reacted

with the compounds on that metal and dissolved them off.

'That demo has sharpened my appetite.

'Apart from a small appetiser,

'it's been a while since I last ate.

'It's time to test the digestive powers of my own gastric juices

'with a substantial meal.'

OK, bring on the food!

Hooray!

I have been waiting a long time for this! Thank you.

So this is the first green thing I've seen for about three days.

Mmm!

'It's not the most relaxing place to eat.

'But that doesn't stop me polishing this off in no time at all.'

Ah!

And over the next few hours, my stomach gets to work.

So this is my stomach having eaten,

and the picture is very different to when it was empty, isn't it?

Yeah, it shows what a fantastic job the stomach can do.

It's really done a blenderiser's job here.

I think I saw something which was

probably the beetroot going past as well.

A sort of red thing. Ooh, there is a great big leaf!

-There's a leaf there.

-And it looks like beetroot there on the top.

-A bit of pinky stuff.

-A bit pinky there.

-Yeah.

The leaves will be a lot of fibrous material,

which is much more difficult to digest.

So that may stay that way for a little bit longer,

whereas the white bits are probably the chips,

so they're now dissolving in the gastric acid.

So that's more of a mash of stuff.

What happened to the steak, then?

It's interesting that we don't see lumps of meat.

You would think that that would be the case.

But the meat will be broken down into fibrous material

by the action of chewing,

And then will be acted on by gastric enzymes and gastric acid

to such an extent

that you can't actually recognise the meat in the stomach.

You can recognise the plant material, and some of the carbohydrate,

the starchy material, but no lumps of meat there.

With a big meal of steak and chips inside me, my stomach has expanded.

But by how much?

What, in size, yeah?

You answer, darling. I haven't a clue.

I think it can get REALLY big.

Probably double in size?

That much?

Like this?

This size?

This big?

-HE LAUGHS

-No, that's too big!

-My fist.

-A small rugby ball.

A medium-sized melon.

I reckon a good...

I think two litres.

She's right.

The average human stomach can expand

from the size of a small apple when it's empty

to about two litres when full.

That's a 40-fold increase.

And it's now clear that this expandable bag of muscle

has more subtle and powerful ways to influence how and when we eat

than was ever previously imagined.

Father-of-four Bob Laquenpaal rarely feels full,

no matter what he eats.

No, I don't want salad.

'About nine, ten o'clock, I have my first breakfast.

'A couple of toasts, bowl of cornflakes.

'Lunchtime is normally a couple chapattis

'with some chicken or vegetables.

'After my lunch, if I'm feeling more hungry,

'I just get a bowl of cornflakes, or Weetabix.'

In the evening, I'll get some chips, a burger...

and later on, a chapatti.

If I'm feeling a bit peckish, I'll buy a big crisp bag,

-and just munch away.

-HE LAUGHS

I just can't get full.

-I want to eat everything!

-HE LAUGHS

Bob is almost 20 stone.

And being so overweight has had serious consequences.

Six years ago, he had a major health scare.

I was at home.

I was lying down, and next minute,

I'm getting pain in my jaw and in my arm.

So I thought, "Something's wrong.

"Let me just drive to the hospital."

So I drove there, and they said, "You're having a heart attack."

I was about 28 at the time.

You're young, I mean, getting a heart attack,

I was just devastated, yeah.

Bob tried going on a diet, but couldn't lose enough weight.

He and his doctors have decided to take more drastic action.

Bob is about to have a gastric bypass operation.

The size of his stomach will be radically reduced.

Now, what are you going to dream about today?

-BOB CHUCKLES

-Mmm?

BOB CHUCKLES

His doctors expect the operation

to have a dramatic effect on his appetite.

For Bob and his family, it's the best hope

of bringing about the health changes that he desperately needs.

-OK, dizzy coming?

-Yeah.

OK. Take three, slow, deep breaths.

At the end of the third one, things will be much better.

You're drifting gently off to sleep. Good.

I'm here at Charing Cross Hospital to watch Bob's surgery.

His surgeon is leading bariatric consultant Mr Ahmed Ahmed.

All right. John, are we ready to start?

He will operate on Bob

using the latest techniques in keyhole surgery.

So, I've gone through the skin and the yellow stuff there is fat.

We have to go through the fat,

and then through the abdominal wall muscle there.

The first quick peek inside,

we're going to see that all the yellow stuff here you see is fat.

The first stage of the operation is to shrink the size of the stomach.

That little, pale pink organ coming up,

that's your stomach, right there.

And you're essentially going to reduce the size of that?

-Yes, absolutely.

-By what sort of amount?

We'll probably make it about a tenth of its normal size.

10% of what it has at the moment?

-Wow. That's quite radical, isn't it?

-Yes.

The total volume is going to be about 20ml,

which is about three or four tablespoons.

So 90% of the stomach will just be kind of left there, inactive?

Exactly.

It's still going to have its blood supply,

and it's still going to make gastric juices,

but it will never see food again.

'And, surprisingly enough,

'it's not just Bob's stomach they're affecting.'

Now, you might think that just by reducing the size of the stomach,

that's how he's going to sort out Bob's problems,

because a smaller stomach, you eat less...

it's sort of straightforward.

But actually, the mechanism by which it works is completely different.

And it's only relatively recently that they discovered WHY

doing gastric bypass is so effective.

The modern thinking actually is that by making a smaller stomach,

you're actually inducing the changes

in various chemical messengers,

which in turn affect hunger levels and fullness levels,

which in turn cause the weight loss.

Mmm.

'So, as well as reducing the size of Bob's stomach,

'the point of the operation

'is to change the levels of certain gut hormones.

'These chemical messengers

'are released by the gut in response to food,

'and tell the brain when to eat, or stop eating.

'One of the hormones, ghrelin, makes you feel hungry.'

We think that ghrelin is actually being produced

from this part of the stomach up here. This fundus.

This is called the fundus of the stomach,

and this is where all the cells that produce ghrelin are sort of based.

Now what we think we're doing

is we're actually separating that part of the stomach completely

from ever seeing food.

So the food will never touch those cells that make the ghrelin.

'Once they're isolated, the ghrelin cells no longer function normally.

'Hormone production will be reduced, and Bob should feel less hungry.'

It's extraordinary, isn't it?

That little area of the stomach can be responsible

for how hungry you feel?

The next stage of the operation

is to re-attach Bob's smaller stomach back to his intestine.

Good, thanks.

'From now on, it will be right next to the part of his intestines

'that produces the gut hormone, PYY, that makes him feel full.'

How long does food normally take to get there?

-Uh, probably about 20-30 minutes, I would imagine.

-Right.

So instead of taking, say, 20 minutes for your brain

to get the message, "You're full, stop eating,"

-it might take five minutes?

-Yeah, about five minutes.

Mr Ahmed believes the operation

will have an immediate impact on Bob's appetite.

Patients who would normally eat three-to-four meals throughout a day

eat maybe just one or two meals after surgery.

And when they do eat, they eat really small portions.

Through side plates, or children's portions,

because they just don't feel like eating the same amounts

as they were before.

And they're happy.

It's not like something that's imposed on them.

They actually are very satisfied.

What I find really astonishing about this operation

is that the effects are so profound and widespread.

Because, in essence, what he is doing

is just sort of making the stomach smaller and connecting the bits,

and yet, the effect on Bob will be enormous.

We think that the brain rules our decision-making process,

but it's pretty clear from this

that our stomach has a very, very profound effect

on how we behave.

Six weeks after surgery, Bob is certainly slimmer than he once was.

Since the operation, I have lost three stone.

I was 20 stone.

Yeah, I've been losing weight, and all my clothes are all loose.

Crucially, Bob's urge to eat lots of fatty foods has gone.

I had a bite of a burger. I couldn't swallow it.

So I'm keeping to my diet.

I only drink a Cup-a-Soup and I'm full.

I'm happy with that, and I can stick with that.

Dad!

It's just great. The family is happy, I'm happy.

I can't wait to lose more weight.

CHILDREN GIGGLE AND SHOUT

The camera has now been travelling inside me for over four hours.

It's made its way through

the acidic and forbidding world of my stomach,

and embarked on the longest part of its journey.

The small intestine, or small bowel.

Over the next few hours, as it travels along this tube,

my steak and chips will be broken down, absorbed,

and transformed into the energy needed to run my body.

As for me, I'm taking it easy.

Ooh, it's amazing how contented you feel after a nice big meal.

Also how tired and slothful.

STOMACH GURGLES

And I suppose it's no surprise I'm tired.

There's a frenzy of digestion going on inside me.

As I snooze, the tight folds on the wall of the small intestine

and mixing and churning my mushed-up food in a corkscrew motion.

Digestive enzymes from the pancreas and gall bladder flood the area.

These enzymes induce chemical reactions,

which break the food down into nutrients

that my body can readily absorb.

The walls of my small intestine look a bit like a fluffy towel.

And they are there to aid absorption.

So, on the folds here, on the folds of the small bowel,

you can see the finger-like projections

of the small bowel lining, which are called villi.

What they do is increase the surface area of the small bowel hugely.

What sort of surface area are we talking about?

About a tennis-court size, if you strip it all out.

So it's really huge.

There is a huge amount of work that goes on in there.

And all this work requires a healthy blood supply.

As I'm lying here, digesting my steak and chips,

a third of my body's blood is being diverted

away from my extremities and towards the action in my guts.

There's active noises down there!

And as this blood rushes through the vessels

in the wall of my small intestinal,

it's picking up digested nutrients,

and transporting them all over my body.

But this could take another three or four hours.

So there's time for me to get more hands-on

with another digestive system.

-Ooh, yes!

-Here we go!

-That's a treat, isn't it?!

'Surgeon and gut specialist James Kinross

'has brought along the intestine of an animal

'that was destined for the food chain.'

So what we have here, this is a pig,

from mouth down to the anus at this end here.

Right.

'Although we don't look much like pigs on the outside,

'their intestines are remarkably similar to ours.'

And what you can see is that

the gastrointestinal tract is basically a tube,

and it runs from your mouth all the way down to your bottom.

-OK.

-So what you have is the oesophagus at the top end,

and we can actually trace all of this bowel, the whole way down.

'The walls of the small intestines feel surprisingly delicate,

'and they are threaded with tiny capillaries.'

-What you'll see is there's a layer of connective tissue.

-Oh, yes.

So the bowel has this connective tissue which takes the blood supply.

And you can see the blood supply here.

So when you absorb a meal, obviously the nutrition you take out of it

has to get into the blood supply.

That's what's happening to me.

So let's see how long this is.

'The human small intestine is roughly four metres.

'The length of this table.

'A pig's is much longer.'

Return journey!

Keep going and keep going.

'Our intestines absorb about seven litres of food, fluid,

'and gut secretions every day.'

-Isn't that majestic?!

-Yeah!

'But perhaps the most extraordinary thing about the intestine

'is that, buried deep inside its tissue,

'is a very thin layer of brain.'

When you think about your brain,

normally you think about the thing up there in your skull.

But you actually have a second brain deep down in the gut.

It's made up of cells like neurons,

which you also find in your main brain.

And, in fact, there are over 100 million of them.

As many as you would find in the brain of a cat.

The neurons are spread out in a thin mesh

that extends all the way from the throat to the rectum.

This brain in our gut orchestrates our digestion.

It's also involved in gut pain.

And surprisingly enough,

the way we respond to pain seems to be linked to our personality type.

I've got a personality test here which I've got to fill in,

which could be dangerously revealing.

It says a number of characteristics here may or may not apply to you.

I've got to score between one and five

for each of these particular characteristics,

where one means disagree strongly,

and five means agree strongly.

So, first up - "Is talkative."

I think...I do like talking.

I'll give myself a four. Agree a little.

"Tends to find fault with others." No. Two on that.

'This test is designed to analyse

'the broad traits that make up the human personality.'

"Is original."

I'm going to give myself a five on that one!

'Of these traits, two have been strongly linked to the gut.

'Being extrovert and being neurotic.

'Extroverts tend to be the life and soul of the party,

'whereas neurotics are quieter, more anxious,

'and often put a negative spin on events.'

Nope. No, I don't like quarrelling.

"Can be tense." Yes, I can be tense.

Er...sometimes, sometimes not.

'Most people are predominantly one or the other.'

I think I'll give myself a four on that.

Three. Five. One. Four. Not overly so.

OK, that's complete. I'm going to send it off for analysis.

It'll be interesting to see what they make of it.

My test will be analysed at the Wingate Institute in London,

by gastroenterologist Dr Adam Farmer.

So what we're trying to do in this study

is to relate personality to pain responses

and to try and link the two together.

'Adam reckons that my personality

'will influence the way the neurons in my gut

'respond to pain he's about to inflict.'

Just rest your arm there. Just so you're nice and comfortable.

'These findings are important

'because they could change the way doctors treat chronic gut pain.

'The test involves once again, sticking a tube

'down my nose and into my gullet.'

So once it's down and sat in your gullet,

-around about there.

-Yeah.

Then we'll inflate the balloon to cause pain.

Oh, God!

OK, here we go. Slight tickling at the back of your nose there.

'Adam has found that the guts of extroverts and neurotics

'respond to pain in very different ways.'

Well done. So the tube's down.

-You're quite safe now.

-HE COUGHS

'I may be safe, but I fear the worst is yet to come.'

HE COUGHS

We're going to give you a series of seven painful stimuli.

I'm going to inflate the balloon up to your pain-tolerance level.

And what I mean by that is to the point

where you can't tolerate any more.

Where you've had enough.

-Are you ready?

-I'm ready. And you're ready?

-I'm just about ready.

-OK.

Ooh, yeah!

OK!

Unpleasantness is seven to eight,

and absolute pain, about an eight.

Uh!

Bloody horrible!

'To see how my body responds to pain,

'Adam monitors my heart rate and blood pressure.

'I'm expecting them both to rise,

'because that's what the textbooks say.'

So the pain's coming now.

Oow! Yeah!

I am keen for you to remove this thing now.

So, the results.

'If Adam is right,

'my pain response will be determined

'by my personality type.'

Your psychological results

-were extremely interesting!

-HE LAUGHS

In terms of...what do you feel your personality traits are?

Because it's often a good suggestion...

Yeah, I think I'm probably...

inclined towards the neurotic.

People when they meet me, they assume I'm more extrovert,

but actually,

I suspect I'm a neurotic posing as an extrovert.

And absolutely!

They were very much the results from your personality questionnaires.

That out of a possible 100 on the neuroticism scale,

-you scored 75.

-OK!

'And as a neurotic, the changes in my heart rate

'and blood pressure were exactly what Adam expected.'

So we can see that, in response to the balloon,

you actually dropped your blood pressure

and slowed your heart rate down

for a transient couple of seconds.

I find that really, really surprising, I must admit.

Because I would absolutely have expected them to go up.

I've always been taught pain, basically,

your heart rate goes up, your blood pressure goes up.

Your body doesn't like it.

'It seems, however, that when neurotics are hurt, the vagus nerve,

'a nerve that connects your brain to your gut, becomes more active.

'This causes heart rate and blood pressure to drop.

'Which in turn, is believed to have a calming effect,

'reducing the amount of pain that's felt.'

-And you don't find that in extroverts?

-No.

Extroverts tend to have the more classic, heart rate goes up,

blood pressure goes up.

'For Adam, the results mean that neurotics and extroverts

'could be treated for gut pain in very different ways.'

For instance, those who have high neuroticism scores,

we would use psychological techniques

such as cognitive behavioural therapy.

Whereas the more extrovert ones,

we may well use pharmaceutical or drug therapy in these patients.

Brilliant. I have to say, I rarely go in for an experiment in some form

where I'm genuinely surprised at the end.

But I was genuinely, genuinely surprised by this one.

Great! Well, you were an excellent subject and you did extremely well!

Thank you!

Ooh, yeah!

It's been almost nine hours since I swallowed the camera

and began life as a museum exhibit.

During that time,

the camera has travelled over five metres through my guts.

But from now, things will really slow down,

and move along at an even more leisurely pace.

We're at the outer reaches of this alien world.

The large intestine, or colon.

You can see that the lining of the colon

is very much flatter and whiter than the small bowel.

And you can see the little blood vessels running through

very, very clearly in the colon.

Right.

It's very weird, isn't it?

It's a big organ, so you can often see a big hole,

whereas the small bowel is very long, but very small in diameter.

COLON GURGLES AND RUMBLES

Through the flatter, wider surfaces of the colon,

water is being drawn out from what remains of my food.

We have some slightly more formed material in there.

HE LAUGHS

That's Mark's polite way of saying

that what we're looking at is faeces.

But it's not just leftover food.

A third of the weight of my faeces is actually bacteria.

There are trillions of them, and they form their own mini-ecosystem.

They feed on the food that my small intestine wasn't able to digest.

Helpfully breaking it down into nutrients, and also making vitamins.

From their dark, dank home in the colon,

these bacteria play a critical role in keeping us healthy.

Most of us don't want to think too hard about faeces.

But I'm off to meet a scientist who is absolutely fascinated by it.

And she claims that you can learn an awful lot about somebody

simply by examining their excrement.

Well, I've sent her a sample of my own,

and I'm off now to discover just what she has learned about me.

Microbiologist Dr Gemma Walton spends her professional life

investigating the different bacteria that colonise our guts.

It's important work,

but her research does give her laboratory a very distinctive odour.

Eurgh! God!

-HE COUGHS

-Oh, that is... Hello, Gemma!

-SHE LAUGHS

-Hi, there! Nice to meet you!

I'm not sure I should shake hands!

That is...that is a truly revolting smell!

It's..erm...a lovely lab smell!

It's not a lab smell!

It's the worst bathroom, pooey smell!

'Inside these flasks,

'Gemma has recreated the conditions found in the human colon.

'She uses this to study some of the huge variety of bacteria

'that live there.

'Each of us has our own unique mix of different strains.

'And Gemma has been looking at mine.

'First up, lactobacillus.'

So, lactobacillus is a big group of bacteria

associated with some quite beneficial effects.

'As well as helping break down food, lactobacillus excrete acid

'which fights off other more harmful bacteria.'

So these are good guys?

So, yes. These are your own good guys.

'But she's also find some species that don't sound so friendly.'

If you have a look at that plate there for me.

-Do you see some pink colonies on there?

-Yes.

Now, those pink colonies are likely to be E. coli.

Right. E. coli, I think of

as food poisoning, infections of the urinary tract...

Well, E. coli are often associated with those events.

However, there are many, many different strains of E. coli.

So it is not necessarily something negative.

In fact, I would be more surprised

if I couldn't find any within your sample.

-So they're a perfectly normal part of the gut balance.

-OK.

'Gemma reckons I have over 1,000 different strains

'of bacteria in my faeces.

'And fortunately, I have a healthy mix.

'But that balance can become upset,

'leading to diarrhoea and irritable bowels.

'If that happens, the good guys may need help.'

So there's two ways that you can do that.

It's the prebiotic way,

so the prebiotic is the food you eat

that then is a food for your bacteria.

So that can help increase numbers of your beneficial bacteria.

The other way you can top up the good bacteria

is by consuming probiotic products

that actually have their own live bacteria in.

And you're introducing them into your gut by consuming them.

In some cases, that's not enough.

Another lab, and more faeces.

This time, St Mark's Hospital in London.

Gastroenterologist Dr Ailsa Hart

is working with colleagues from Imperial College

on novel approaches to rebalancing gut bacteria.

The most drastic of which involves performing a faecal transplant.

-Hello, there!

-Hello!

-Michael. So what's happening in here?

We're just in the process of preparing a sample

for a faecal transplant that we're doing as part of a research trial.

'In this pilot study, faeces from a healthy donor

'are transplanted into the guts of patients

'suffering from a condition called pouchitis.'

Pouchitis is a form of inflammatory bowel disease,

and normally that's treated very simply with antibiotics,

but in a small group of patients, when the antibiotics haven't worked,

the next line of therapy becomes a little bit trickier.

And it's in that group that we're going to try this technique.

They are hoping to replace the unhealthy mix of bacteria

in the patient's guts with a healthy mix of someone else's.

First, the donor faeces are blended with salt water...

..and then filtered.

It sounds, I must admit, slightly revolting!

It does sound revolting! It sounds disgusting!

But this is for a group of patients

who have had a lot of therapies beforehand,

troubled by lots of diarrhoea, awful incontinence,

and really dreadful quality of life, actually.

The next stage is to put the faecal solution into the patient.

We take a nasogastric tube.

-Down the nose, presumably?

-Down the nose, into the patient's stomach.

And then it's simply the syringe goes on to there

and you put it into the patient's stomach.

-And it just goes straight in?

-Straight to the stomach.

Dr Hart is looking for signs that this radical approach

will improve her patients' symptoms.

So by giving this transplant, are we able to alter the bacteria

in the guts of these patients,

and is it having a clinical benefit in them as well?

It's early days, and so far,

only a handful of patients have taken part in the study.

It's the most densely-populated ecosystem on the Earth.

So to try and understand it is a very tall order.

To try and modulate it...you know, you do ask the question,

-"Are we, as human beings, clever enough to do this?"

-Mmm.

Back at the Science Museum, my food has been digested and absorbed.

What's left has been chewed over by my gut bacteria

and is now nearing the end of its journey.

But faeces are not the only thing

that the bacteria in your gut produce.

Flatulence. All of us produce gas.

I guess the question is, how much do we produce? Any guesses?

I would say about seven times a day.

Ooh, about 12 to 15.

100 times?

25-30.

I always thought it was 13.

I haven't farted so far today! THEY GIGGLE

-You farted on the way here, in the coach!

-No, I didn't!

-A few hundred.

-20 or 30.

Five?

-Five times a day?!

-Yep.

-No, it's a lot more.

5,000.

There could be ones that you don't even notice. You know, involuntary.

'In fact, we're letting out an average of 12 to 15 every day.

'Typically releasing about two litres of gas.'

I was looking to see what he had going on!

'Fortunately, according to Gemma, not all of them are smelly.'

Well, there's two types of flatulence.

Some people have very odorous flatulence and some people less so.

HE GIGGLES

'If you have particularly unpleasant flatulence,

'blame the mix of bacteria in your colon.'

'Some produce pungent hydrogen sulphide gas,

'others the less odorous but more flammable methane.

'And just as diet can affect the balance of good and bad bacteria,

'so it can alter the balance of sulphur to methane producers.'

By changing your diet,

you might actually increase the amount

of hydrogen sulphide produced.

If you're eating quite a sulphate-rich diet.

Which are the foods that actually produce the worst flatus?

It would be things like beer and wine,

breads, vegetables.

Vegetables? This is a reason not to eat vegetables!

No, not at all!

Flatus is actually a really, really healthy side effect

of eating fibre in the diet.

So it's something you really want to be doing!

HE GIGGLES

Right, I thought I'd share with you, this is the essence, if you like, of really horrible flatulence.

It's a sulphide group,

and I thought that you would be keen to have a little smell.

-CROWD GROANS

-No, thanks!

-It's fine!

What do you think?

-HE LAUGHS

-Does anyone recognise the smell?

These are sulphides.

No? Not for you?

HE COUGHS AND SPLUTTERS

That's really, really revolting, isn't it?

Maybe it was the smell that put them off.

But it's late, and the Science Museum is about to close.

The day has certainly been eventful.

And this alien world in my guts is a bit more familiar now.

There's still quite a lot of gunge around there, isn't there?

'Time for one more peek at what's going on inside me.

'And there's one last question on my mind.

'When's the camera going to come out?

'I know it will work its way out of my system,

'and that could happen sooner rather than later.'

I think I need to go urgently to the loo! I will be back!

I'll see you shortly.

That's good.

It might come out yet!

Urgh!

Mmm!

Mmm!

'Over the last 12 hours, as I've digested my food,

'my guts have been under intense scrutiny.

'They've been poked and prodded in more ways

'than I could have possibly imagined.'

Brings tears to your eyes!

Oww!

'Along the way, I've discovered

'that what goes on inside this mess of tubing

'not only profoundly affects our health and wellbeing,

'but our behaviour too.

'My experience as a museum exhibit

'has left me with a huge respect for my gut and its inhabitants.

'They are working together

'with an intelligence and complexity

'that we're only just beginning to understand.

'And as for the camera,

'it did eventually find its way out.

'But that's one part of this process that I'm going to keep private.'

Subtitles by Red Bee Media Ltd