Horizon (1964–…): Season 50, Episode 6 - Sugar v Fat - full transcript

We're doctors, brothers, and twins,
and we both love to eat,

but which is worse for us -
fat or sugar?

It's the hottest question
in nutrition right now,

with sugar in particular
being targeted as public enemy no 1.

Sugar is the thing that's making you
specifically sick.

We're going to find out
if too much sugar or too much fat

can make you sick
or pile on the pounds.

You're a quarter fat!

One of us is going
on an extreme high fat diet.

This is Tiger.
Tiger is basically on my diet.

The other, on an extreme
high sugar one.



None of these foods have any fat,
do they?

It's a high-carb, sugary diet.

During these month-long diets,
we'll be testing how our minds...

I bought loads of them!

..and our bodies
cope with just eating fat or sugar.

I feel like I'm out of juice.

And what we discover is really
surprising and really unsettling.

It overturns my entire way
of how I think about my body.

I'm not well!

But after meeting this scientist

and some cheesecake-eating rats,
we found that the latest

scientific research changed what we
thought we knew about fat and sugar.

Total opposite of I think
what we would expect,

what most doctors would expect,



what most people in the street
would expect.

And it has the potential
to do the same for you.

I'm Dr Chris van Tulleken,

and I'm a specialist
in infectious disease.

Here in Britain, fat's traditionally
been seen as the major problem.

When I trained as a doctor it was
clear that fat was the enemy

because it raises your cholesterol

and it blocks up your arteries,
causing strokes and heart attacks.

Over in America, it's sugar
that's under attack.

I'm Dr Xand van Tulleken and my
speciality is in tropical medicine.

Now, in the States, sugar
isn't just regarded as unhealthy -

some people are even
calling it toxic.

So, who's right?

It's a question that's fascinated us
as doctors, and by a quirk

of birth, we have a head start
in getting to grips with it.

Chris and I are identical twins,

which means we're genetically
the same,

so we're in a really nice position
to do an experiment on each other.

Now, I live in New York
so I get constant messages

in the media about how fat
is good for you and sugar is

really the enemy, so I'm going to
go on a high fat, low sugar diet.

And although in Britain
we do get this message,

it's not as pervasive, and I'm
convinced if I go on a low fat,

high sugar diet,
I will stay healthy.

So who's right? The Americans
who think that sugar is really toxic?

Or the British, who think that fat
is the deadly ingredient?

We're going on extreme diets
based on the sort of techniques used

in scientific research,

although we are a rather
unscientific sample of just two.

We want to know what they do
to your weight and how

they affect lifestyle diseases
like heart problems and diabetes.

Nutritionist Amanda Ursell
is on hand to make sure

we get it right,
and that it's edible.

If we kick off with Chris.

Chris, you are on the high sugar
diet. Yeah. I can see that.

People tend to
think of sugar as this,

the white stuff in the bowl,
but actually all of this food

ultimately gets broken down
into blood sugar.

So, you are allowed bread
and bagels, pasta, rice,

potatoes, any description
of breakfast cereals.

And what's this?
That's, er, a fizzy drink.

And you can have some fruit and veg.

Well, you can have
unlimited fruit and veg.

And they've all got sugar
and none of these...
these foods have any fat, do they?

It's designed to be very low fat
and it's a high carb sugary diet,

and that's what you can live on
for the next month.

For Xand, this is your bit here.

Basically, you can have cheese,
you can have meat, you can

have steak, you can have burgers,
it's chicken with the skin on,

you can have double cream in your
coffee, you can have mayonnaise...

The kind of thing you would do.
But you're not allowed any fruit,

and you're not allowed very much
of this veggie stuff at all.

My problem is that I'm not going
to have a poo for a month, am I?

Well, there are disadvantages.

Firstly, your girlfriend
doesn't want to kiss you

because you have bad breath.

Constipation, yes, you're right.

I'm getting almost
no fibre in any of this, am I?

Very limited fibre.

I think I'm going to be craving
a bowl of fresh greens

by the end of a few days.

I'm sure you are.

What do you think, Xand? I mean,
I feel like you got the better deal.

It's difficult
cos I'm going to have bad breath

and I'm not going to poo. Mm.

But I get to have bacon
and eggs for breakfast.

Just to be absolutely clear,
we can both eat as much as we want

of the things on our bit
of the table?

Yeah. That's what we want you to do.

These diets are going to be
quite hard to stick to,

so we're going to film them.

We're going to make video diaries
using our phones.

So at least for the duration of the
video diaries, Xand won't be able

to be shovelling
carbohydrate into his mouth.

Just woken up, and what I feel
like is a massive stack of pancakes,

with maple syrup.

The point is, if I have to tell
into my phone every day

what the experience is, I can't lie.

Keeps us honest. Yeah.
That's the plan.

What we're going to do now is sample
how much oxygen your body consumes.

Food is, of course,
the fuel that powers our bodies.

But just how it does that is subject
to complex metabolic processes.

Dr Richard MacKenzie studies
how these processes influence

diseases like diabetes.

It's long been thought that eating
too much fat can make us fatter,

and that saturated fat
can raise our cholesterol.

High amounts of cholesterol
are quite bad for us.

They block our arteries
and that blocks blood supply

to the brain and heart,

so that's quite dangerous.

Eating or drinking sugar,
on the other hand, releases insulin,

a hormone that
regulates our blood sugar.

Eating too much sugar
can make us fat,

and could potentially
lead to diabetes.

We're going to be checking to see if
our cholesterol and insulin levels

go up or down over the next month.

What's nice about this experiment,
it's not a big experiment,

but we're well-controlled,

and so we really should get
a robust answer from this. Yeah.

OK, gentlemen, what I need you to
do is to pop behind the curtains

and strip down into
your boxer shorts, please.

We're expecting these diets
to have an impact on our bodies.

And one thing we're focusing
on are changes not to just to fat,

but also to muscle.

Shifting fat is good,
but losing muscle isn't healthy.

You do look very different
to when I last saw you,

and I must look different as well.

Yeah,
you've got a little bit fatter.

The first time in a few years
we look a bit like twins.

OK, gents,
we'll just go for the bod pod now,

I can see you're both a little cold.

It's freezing in here.

I feel a bit underdressed.

MACHINE: It is important
to remove any jewellery,

shoes or eyeglasses before weighing.

Here we go.

Enter the bod pod,
then close the door to begin test.

This machine measures
the ratio of fat to muscle.

So Richard, we know that being fat
isn't good for you, but why do

we need all this fancy equipment
to measure it so precisely?

It's to help improve
our understanding of exactly what

increased body fat is doing,
and we know that it's

linked to a number of diseases
that reduce our life expectancy.

So things like cancer, diabetes,
heart disease, strokes,

hypertension, to name just a few,

all are related to
an increase in body fat.

It's the same noise as the Batmobile
canopy coming out. Mm.

Close the door to begin test.

And now we freeze him
and send him into outer space.

Yeah, that's the plan.

So we've got the results
from the body composition test.

So can we try and guess? Before you
tell us, can we try and guess?

Please do. I think I'm 25%.

I feel like someone who almost
a quarter of their body is fat,

that's how I feel.

You're pretty much spot-on,
you're 26.7% body fat.

Spot-on,
but slightly more than spot-on.

Good news for Chris is,
he's 22% body fat.

Oh, so we're pretty similar.
Oh, that's quite good, actually.

I mean I think, you know,
there is going...you know, he...

So am I overweight? Um, well, we'd
have to look at your BMI for that.

Don't pull the punch. Yes.

A little. You're a quarter fat!

Look, Richard's being
so nice about it! "A little,

"I mean, we couldn't -
we'd need to look at the chart."

All right, all right, I get
the message, I get the message.

And he's OK, is he? A fraction over,

um, but certainly on the healthier
side of 20, 22.6%.

I'm letting you down.

You're letting your genes down.

Yeah, sorry about that.

I'm eating a little piece of turkey
rolled up in a piece of cheese.

I'm eating everything
with my fingers now!

We're two weeks into the diets,
and we now want to start

measuring how fat and sugar
are affecting our bodies.

And the place we want to start is
with our brains.

Everything goes through your brain,
every decision you make,

every action you take.

So it'd be pretty important to know

if cutting out fat or sugar
affected how well your brain worked.

At some point, we've all felt
the pressure of mental stress

and tension, but how does what you
eat affect how you deal with it?

And there are fewer more cognitively
demanding environments

than a city day trading room.

So, we're going to put our diets
to an extreme mental test

by becoming stock traders
for the day.

Chris, on his high sugar diet,
is in London,

and I'm on my high fat diet
in New York.

So Chris, do you have any sense that
you're going to be any good at this?

It is like the Matrix.

I'm looking at a financial
horror show, this is just a mess.

I mean, no wonder
the economy collapsed.

How could anyone understand?

OK, so that we have a bit of help,
JJ is going to give us a hand, OK?

JJ. Hey, Chris, you've got to have
a better attitude going in, buddy,

you're a smart guy,
it's not that hard.

X axis, Y axis, it's...

It's buy high, sell low, yeah?

Er, buy low, sell high.

The other way.

OK, trade,
and right there you see a bid.

After a quick lesson with JJ,
we're let loose on US-based

TD Ameritrade's paper money
application, and we've got

100,000 dollars of pretend
money to play with.

Yeah.

It was a pleasure, guys.
Chris, good luck. Xand, good luck.

May the best twin win.

Right. And thank you very much,
fellas.

I can buy a bit of that.

I'm going to buy some more
companies now.

I'm into it now.

Ten of oil, light sweet crude.

If the oil comes up then
I will have made a bunch of money.

OK, so now the pressure's on
cos I've spent all my money.

'Watching closely in the background
is Professor Robin Kanarek.

'She studies the effects
of diet on cognition,

'and she thinks
I might be in for a hard time.'

Don't know what any of this means.

This is an extraordinarily difficult
task because there's many

different aspects of cognition
that have to be involved.

He has to first pay attention, then
he has to remember what he's done.

What I can't remember is how many
I bought and how many I sold.

And then he has to make decisions,

what we call executive processing,

he has to decide whether to buy
or sell.

So he's got multiple things
that are going on at the same time.

Oh, no, I bought loads of them.

See, now I've got negative money,

and no way of getting back
out of the hole.

My problem is that being on
a high fat diet could limit

the fuel for my brain.

I'm really stuck on this now.

Glucose is the primary fuel
of the brain

and the best fuel for the brain.

Since he's been on
a low carbohydrate diet,

almost eating no carbohydrates,

his stores of glucose in the body
are going to be very low.

Um, and therefore I think
as time goes on, he may be having

more difficulty with the task.

And I'm short of glucose
on my extreme high fat diet.

But the body has a back-up plan.

It can turn fat into energy
compounds called ketones,

but they aren't as efficient.

In normal everyday life,
that's not a problem.

But when you need to think
really hard, it can be.

I've got the initials in head and I
can't remember what they stand for.

Then I've got to try and remember
something about the companies.

The professor's research indicates
that without enough carbohydrate

in your diet, your memory can be
significantly compromised.

There are certain parts of the brain
that use carbohydrates,

particularly for memory,

and if they're aren't getting enough
glucose, then they can not function properly.

Getting Exile at 97 dollars 29.

Over in London,
things are markedly different.

Chris on his high sugar diet
is more alert, has more energy,

and has a significantly
better memory.

When I'm thinking hard I can
really feel inside my head

brainwork going on,
and this is very brain-heavy,

it's remembering loads of numbers,
remembering loads of initials,

and learning a whole new
language of bidding and asking.

So this screen means
everything's going green

so everything's going up, so you
just have to hope that continues.

I think I might be doing OK
on my high sugar diet,

because the brain consumes 60%
of the sugars in your blood.

For people who are on diets
that have complex carbohydrates,

er, whole grains,
fruits and vegetables,

there's a lot of studies that
show at least on a short-term basis

that having a high carbohydrate diet
will facilitate memory.

It's such fun.

I can see why these guys
get really into it.

It's the end of the test,
so who won?

I can't remember what I wanted to do,

let alone the numbers and letters
I needed to do it.

I'm not cut out for this.

Maybe Chris'll have done better.

So Xand made...Xand made
essentially 300 dollars profit

and I've made over 800 dollars
profit.

So I absolutely thrashed him,

and I tell you what, I could not
have done that if I'd been

feeling hungry or wanting something
I couldn't have, like some sugar,

and a big carb breakfast
is what meant I could do that.

Scientists are now beginning
to understand how certain parts

of our memory
are affected by carbohydrates.

On my high sugar diet I'm eating
all kinds of carbs from starches

to grains, vegetables to fruit.

But no matter what form
the carbohydrates come in,

it's all broken down in my gut

into single sugar molecules,
like fructose or glucose.

And it's the effect of these
single molecules on our bodies

that's at the core
of why some scientists,

particularly in America,
argue that sugar's bad for you.

So Xand's in San Francisco,

to meet one of the researchers
who's led the charge against sugar.

He's seeing Dr Robert Lustig, who's
convinced that the way fructose

and glucose work in our bodies leads
to all kinds of health problems.

Robert, do you want to pause
in the doughnut store

and get a bucket full?
I...I... We'll talk about it later.

For him, glucose and fructose
are dangerous for different reasons.

First of all, fructose.

Turns out, only the liver
can metabolise fructose,

and you have a limit to how much you
can metabolise, just like any drug.

You have a threshold.

If you go over that threshold,
your liver has no choice

but to take that extra energy
that's been delivered to it

and turn it into liver fat,

because that's the way the way
the liver gets rid of extra energy.

So you drink a bottle of soda,
some of it you can metabolise,

but the rest of it
has to become liver fat?

That's right.

And that liver fat can have damaging
consequences for your health.

It can make you more liable to
heart disease, strokes, or diabetes.

But according to Dr Lustig, that's
just half the problem with sugar.

The glucose molecule
activates insulin,

the hormone that controls
blood sugar.

But Lustig believes insulin
does a whole lot more.

Insulin shunts sugar to fat.
The more insulin, the more fat.

Well, guess what? The more insulin,
the more disease, too.

OK. And insulin is really
the lynchpin in this whole story,

because whether you gain weight
and whether you get sick

has everything to do with
what your insulin does,

and if you can keep your insulin
level down,

then you won't drive
energy into fat,

you have a chance to lose weight,

you won't be
making your arteries thicker,

you have a chance for your
blood pressure to come down,

and this is what we've seen,

is, "it's the insulin, stupid."

It's known as the
hormone hypothesis,

because fat cells respond to
the release of insulin by holding

onto fat, and making more of it.

In general, the studies that support
the theory about fructose

only looked at diets with unrealistically
high levels of fructose.

Much more than
the average person consumes.

So I'm not yet convinced
about fructose.

And as for the insulin hypothesis,

the comprehensive study
hasn't been done yet.

So like most scientists in Britain,

I'm pretty sceptical
about these claims.

I'm three weeks into
my high fat diet

and I'm really starting
to miss carbohydrates.

I've got on the plane very early,

which means I can try and eat
my burger quickly

before anyone sits next to me.

It's really hard not to eat
the French fries.

So I'm all done.

This is what remains.

But even though I couldn't
eat the carbs,

I wasn't ravenous after my meal.

What I really want to know is

if that has anything to do
with the amount of fat in my diet?

To try and understand
what's happening,

Xand has to fly back to Britain...

Right, boys. We want you to do
something...

..where Amanda Ursell
has set up what she calls

a hunger experiment.

We start the day eating the same
amount of calories for breakfast.

Xand has a plateful of fat calories,
but mine is chock full of sugar.

Three hours later,
we're offered lunch.

And this is where
it gets really interesting.

Because now, Amanda can test
whether or not eating fat or sugar

has had any effect
on how hungry we were.

Well, I'm jotting down
what you're having,

so I'm going to count all
the calories that you're going

to have, so I know exactly what's
on the plate, so, there we are.

So will we eat the same number of
calories like we did at breakfast?

I'm going to start
with this soup. OK, the soup.

Come on, come on. Go on, then -
off you go.

Start eating. I'm going to
work all this out for you.

We both start hungry,
but that doesn't last for long.

Do you think I'm going to be
able to eat all that?

No, no. Delicious though this all
looks, I'm not really enjoying it.

All right, what else can I have?

We've got some pasta.

Pasta. Yeah.

But is how hungry we feel just
down to the calories we consume?

It's like I just don't want
any more of that.

My brain has just said, "No,
that's it, that's all you need."

Can I take that? I need to measure
what you've left. Absolutely.

Or could it be the macronutrients
in the meals, fat or sugar,

that are governing
how hungry we feel?

On this diet I can still eat
to shame. Really?

To the moment at which I hate myself
more than I want to keep eating.

Can you get that whole meringue
in your mouth at once?

So we've got the results now.

Later, Amanda gets busy
with her calculator

and tots up the final calorie count.

OK, Xand, you're on the high fat
diet, you had 825 calories.

That's quite a lot.
Yes, that's a big meal.

Yeah, but you, Chris, on your carb
blowout, you had, er 1,250 calories.

Whoa! That's...that's half your
calories for the day right there.

That's half my whole day's
calories in a single sitting. Yeah.

For me, the interesting thing is,
I ate more food than you,

so calories do not necessarily
make you feel full,

and I was then hungrier quicker,

so this really simple idea

that we kind of learn that
if you feel hungry

you eat a meal
and then you stop feeling hungry,

even that is not really true.

You can eat an enormous meal and end
up being hungrier than the person

who ate...you know, you ate
almost half the number of calories I did.

What's going on there, then?
Why is that?

There's quite a big body of research
that suggests that

high protein diets
make you feel fuller.

It's the protein
that's making me feel full?

You don't really eat high fat
on its own,

you don't eat butter on its own
or glug down olive oil on its own.

Xand might.

It comes with protein and makes you
feel fuller than the carbohydrates.

That's probably number 1.

But it's more than that.

Protein and sugar have very
different effects on ghrelin -

the hunger hormone.

The more ghrelin you have in your
body, the hungrier you'll feel.

Protein suppresses ghrelin
for longer than sugar.

The problem with sugar is that
it's an easy source of calories,

and that can make you fat.

But you can end up eating
fewer calories on a high fat diet

because of the interaction
with ghrelin.

Not all fats are the same,

and fortunately on my diet
I'm mostly on the good stuff.

I'm eating lots of monosaturated
and polyunsaturated fats,

the kind of thing you find in eggs,
olive oil, and oily fish.

And that's all good for you.

Now, I'm also eating quite
a lot of saturated fat,

which is the kind of thing you
find in foods like meat and cheese.

Now this stuff you're not
recommended to have more

than 30 grams a day
because it raises your LDL,

your bad cholesterol,
but recently an increasing

number of scientists are saying this
may not actually be true.

But there is no debate
about trans fats.

Now, trans fats are found in a wide
range of manufactured foods

like cakes and cookies, things like
this, and they're not good for you.

And what they do is
they not only raise your LDL,

your bad cholesterol, but they lower
your HDL, your good cholesterol.

Fortunately, on my diet I'm not
allowed to have any of them.

A gram of fat also has over twice
as many calories as a gram of sugar.

And our bodies turn dietary fats
into body fat more easily

than it does with sugar.

Ultimately, of course,
fat and sugar are sources of energy.

So what we really want to know
is how they work to fuel our bodies.

It's now going to get personal
and painful.

What we're going to do is we'll have
five minutes steady peddling away,

I'm going to talk to you, I want to
keep a nice conversation going,

and then we're just going to start
ramping it up a little bit.

We set up another test,
this time on a bike.

This is very fun,
I haven't used one of these before.

Have you not? Oh, you're going
to hate it soon.

We've recruited Nigel Mitchell

from the first ever British
Tour de France winning cycling team

to help us.

Perfect, perfect, perfect.
Just nice. Keeping up so far.

This is the first exercise
of any kind we've done in our diet,

and we've not eaten for 12 hours.

Your cadence looks nice.
Drop a gear.

We're 15 minutes into
an hour-long session.

Nigel wants to completely
exhaust us.

Ramp this up a little bit to 18mph
now. Drop a gear? Drop a gear.

Yeah, we're starting to work
a bit more now.

It's the first step in a
particularly sadistic experiment,

to see if fat or sugar is the best
macronutrient for exercise.

So, how much difference does
the kind of nutrition science

you're doing make to a team?

I want to use foods to fuel them,

I want to use foods for them
to recover.

So the foods that we give the guys

is a mixture of bars and gels
and protein.

Breakfast, we use a lot of porridge.

Now you can't get porridge
on the continent,

so for the Tour de France
and all this we actually buy

the porridge oats in this country
and we take them out there.

And last year it were about
three weeks before the tour

and I go around my local supermarket

and I've got all my Sky kit on
cos I'm working, and I've

got a trolley full of porridge oats,
I've got about 80kg of trolley oats.

I put them on the conveyor belt
and we take them through,

and the woman on the conveyor belt,

woman on the till just brings you
down to Earth, she says,

said to me, "So do you work in
a care home or something, you know,

"all this porridge oats
that you've got?"

45 minutes in,
Nigel takes a blood sample.

'The blood test confirm just how bad
we feel.

'Chris is burning sugar like crazy
and his blood sugar levels

'plummet from 4.7, where they were
at the start of the test, to 2.7.

'I'm faring better. My blood sugar
has fallen by only about 25%.'

This is doing exactly what
we wanted it to do.

Last minute, then, boys.
Just keep it like this.

'An hour of punishing exercise
without food has pushed us to the

'edge of our physical capabilities.'

Yeah, I feel like I'm out of juice.

'We're now both exhausted and empty,

'which allows Nigel to test how
fat and sugar fuel the body.'

OK, boys, so we've done the hour
on the turbo trainers at the top,

we've pushed your blood sugars down,
so you're just mild hypo...

Get off! What we're going to do now
is race up the hill.

Now, we've got some food,
so for Xander, we've got butter,

so it's one pack of butter,
please. Just one.

And then I want you to take
one in your pocket for eating

on the way up,
and then we've got a gel for you.

The same number of calories
in the gel. Roughly.

We've got the same number of
calories in the gel as the butter.

But the gel is sugar.

'There's nothing special about
either the butter or the gel.

'They're basically fat and sugar.'

So, right,
I want you to ride at my pace.

I want us to control this,
as we're going up there.

A little bit easier on the gears.
That's it, perfect.

You're in the same gear.

'Now it's time for the race up
the hill, between fat in red

'and sugar in blue.'

When we turn right, we're going to
start just lifting it slightly.

Are you OK? Yeah, I'm all right.
Just push on a bit more, then.

'We're climbing the iconic
and steep Box Hill in Surrey.'

'And in the next few seconds,

'it's going to turn into a fat versus
sugar race to the summit.'

What's your heart rates now,
boys? 177.

154.

Just keep next to each other,
if you can.

OK? Right, are you ready,
both of you? Go!

Keep it going. Keep it going.

'In the race to the top,
Chris soon speeds away from me.'

He just keeps getting further away

and I cannot make
my legs go any faster.

It's like I'm stuck in one gear.

'With my heart rate
pumping at 200 beats per minute,

I just manage to get to the top.'

Just looking at you two,
you've got a big smile on your face.

You won the King of the Mountains
there, Chris.

Xander, you bunked out.
But this is the thing.

This is what we're trying to show.

When you're really trying to push
it, your body needs the sugar.

It needs the carbohydrates.
I want to measure the sugars again.

7.1, your blood sugar now. 7.1.

'Chris's blood sugars are so high
because the sugar gel

'he consumed half an hour ago is
still pulsing through his body.

'And that gave him the fuel to
power his muscles up the hill.

'But what about my
blood sugar levels?'

5.1, now that's interesting.

All we've given you to eat is fat
and we can't convert fat into sugar.

'Completely deprived of glucose,

'our bodies have a dramatic
way of making sugar.

'Protein in the form of muscle
converts into amino acids,

'which are then turned into glucose

'and that's pumped into the blood,
raising blood sugar levels.

'So there's no question you can
power your body without sugar,

'but there is a price to pay.'

Your blood sugars going up has got
to be coming from the protein.

He's burning muscle to make sugar.

He's burning muscle to make sugar
now. I feel quite rubbish.

This is the last state you'd want
one of your athletes to be in.

If we'd got one of our riders
and they were in your state in the

Tour de France then I'd be
looking for a new job.

So we had identical turbos,
we've got identical bikes, we've got

the same tyre pressure,
so you're doing the same work...

We've got effectively
the same person.

Effectively the same person
genetically.

The big difference is the diet
that you've been following.

What's amazing about that is
I haven't eaten any carbohydrate

in weeks and my body can still make
enough sugar to get me up that hill.

How have you done this?

How have you turned your dreadful
performance up that

hill into a kind of victory for fat?
I got here, didn't I?

And... Yes, you did have normal
carbohydrate, which is...

It's a point for me
because your body needs

carbohydrates to exercise like that.

And where are you getting
the carbohydrate? From your muscles.

So you do exercise like that all
day, you'll actually lose muscle

and keep your little belly cos you're

not turning that into carbs,
are you? All right.

I'll beat you on the way down.

Yeah cos you're still fat!
HE CHUCKLES

This meal, it should be so good...

It's missing one essential
ingredient.

And that's fat.

So it's totally joyless.

It's just a rubbish end to my day.

At last, the diets are over.

And we're back at the lab
to find out what effect fat

and sugar have had on our weight
and health.

OK, chaps. What I need you to do is
get stripped off like before.

'We're with our old friend Richard
McKenzie to be weighed and measured.'

OK, no talking, no moving.

'Starting, of course,
with the machine that measures

'the percentage of fat
and muscle in our bodies.'

OK, and you're up next.

'..Then close the door
to begin tests.'

'And he's got some good news and
unfortunately, some bad news for us,

'beginning with the results
for the high sugar diet.'

Chris, OK, you've lost 1kg of body
mass. Is that good?

You've been eating as much as you
want of junk for a month

and you've lost a kilo.

Yeah, it's not bad.

Half of that has come from body fat

and the other half has
come from muscle mass.

Oh, really? So I have lost
muscle as well? Yes. What about him?

I feel like I've lost weight.
You have.

You've lost around 4kg of body mass.

'On the high fat diet,
Xand has lost more weight.

'To be more accurate,
3.5 kilos in a month.'

So, where has that weight
loss come from?

2kg has come from muscle mass,
1.5 has come from fat mass.

I've lost weight, which is great,

and I've lost
a legitimate 1.5 kilos of fat.

In four weeks, that's really good.

On the face of it, that's very good.

Yeah, on the face of it,

but you've lost 1.5 kilos of fat
and you've lost 2 kilos of muscle.

Your brother's right. We have to
look at it in a bit more detail

and losing body weight is an ideal
goal in some circumstances,

but you've lost 2kg of muscle mass
and that isn't healthy.

Why is it so bad to have lost
these 2 kilos of muscle?

If you lose muscle mass,
with disease or ageing,

you are more likely to visit
the hospital more often

and have a poor life expectancy.

Really? Yes. That bad? Yes.

That's a really important
counterintuitive thing,

I think, that we're going to lose
weight, go on a diet, we don't

think too much about exercise,
and it can be really bad for you.

'Nervously, we went through the same
battery of tests as we did

'a month ago.
First, we checked our cholesterol.'

'We thought that because Xand was
eating so much fat on his diet,

'his levels would be much higher.

'What was amazing is that they
were nearly exactly

'the same as they were
at the start of our diets.

'In fact, there was little or no
change for either of us.'

One minute to finish.

'Finally, we tested our insulin,

'the hormone that regulates
the level of sugar in your blood.'

Urgh!

'Naturally enough, on the high sugar
diet, I went first.'

Your body's ability to produce
insulin improved.

That is the opposite...
Totally the opposite

of I think what we would expect,
most doctors would expect,

what most people
in the street would expect.

Probably just got used to
dealing with the sugar,

the glucose intake and therefore,
responding by producing insulin.

A bit like if I'd been drinking
a lot for the month,

my liver would up-regulate the
enzymes to deal with the alcohol.

It's almost the same thing.

Because I've been eating
loads of sugar,

I've become better at managing it.
You're better at producing insulin.

Is that good or not?

Um...

In the short term, it is good,
but long term,

it might produce a problem.

'An unexpected result for me.

'But what about Xand
on the high fat diet?'

What is worrying is your body
is not responding to

insulin as well as it did.

If you eat too much fat, that can
stop your body responding to

insulin and it also can tell
your body to produce more glucose.

So how serious is this? It's only a month.
Is this a big difference that you're seeing?

Actually, it is a big difference.

What we've seen is your blood
glucose has climbed from 5.1,

which it was before the diet,
which wasn't great to start with,

but still in a healthy range,
to 5.9.

You're only 0.2 away from being
pre-diabetic.

Wow!

In a month,
I've done myself some proper damage.

This isn't good for me at all.
It's not good for you.

That's the first thing.
You should stop that diet.

Eventually, your body will stop
producing insulin

if you carry on down this path.

I've been on a no-sugar diet

and I just would have thought
I'd be making less insulin

and needing less insulin. You're
saying I'm making more insulin,

my body isn't reacting to it as well

and I'm well down the road
to diabetes,

which is, which is bad news.

It's bad news, you're heading
that way.

So I thought if you eat
lots of sugar,

you make lots of insulin
and that's bad,

but it turns out me eating lots of
fat makes my body insulin-resistant

so I make more insulin
and that's worse.

So I'm...I'm doing really...

Like, I'm close to being diabetic
now, I'm not...I'm not well!

I mean, was wrong too. Like I...so I
thought, "Well, I'm having coffee,

"I can't have my cream in it,
so I'll put in lots of sugar,"

so I ate so much more sugar
that I normally would...

And I'd have thought that would
make you diabetic or close to it.
That's...that's, I think we all,

that's the received wisdom
of becoming diabetic is about
eating sugar.

When are we ever going to learn that
if you...it's never about one thing.

We say, "Oh, it must be fat
or it must be sugar..."

No, it is ALWAYS more complicated
than that. Always

It's like a really basic rule in
life, isn't it? If someone

is selling you one simple solution
to a problem that everyone has,

it probably isn't going to work. No.

As doctors, we know we have got
to be careful

about extrapolating too much
from our own experience.

Human physiology can be
extremely complicated.

Being on a low-fat or a low-carb
diet yourself, you learn all kinds

of things that you could never get
from reading about it in a paper.

You learn about the experience
of being on it,

whether or not it's fun, whether
or not it's nasty, how it feels.

But the numbers that you get
from an experiment

with just two people
aren't definitive.

They're interesting,
but they don't tell you enough.

To get definitive information
from those numbers,

you have to look at the experiments

that are being done
on thousands of people.

Over the last few years,

as the world's got fatter
and more unhealthy,

finding an answer to the
fat-versus-sugar question

has become even more pressing.

One of Britain's leading
nutritionists, Professor Susan Jebb,

has been researching this
for more than a decade.

And she started with
a simple observation.

We've been looking at this for...for
many years

and I guess what I struggle with
is the idea that,

you know, people start off thin,
or lean...

Uh-huh. ..and at some point
during their lives,

many people end up
gaining weight, becoming fat...

This is me at the moment.

And a proportion of those go on
to become sick and they develop

illnesses, like cardiovascular
disease or...or diabetes.

We're in no doubt about this link,
that being fat makes

a lot of people, not everyone,
but a lot of people ill.

Absolutely, increases your risk
of heart disease,

of cancer and of diabetes.

OK. So is it something about their
diet which alters that risk?

We looked at um...at the amount
of fat or carbs or indeed protein...

'So she set up a series of
long-running, comprehensive studies

'to see what effects
feeding people fat,

'sugar and protein had on
their health and well-being.'

And more than that,
we've tried to study the differences

in these groups, so we've been
interested in saturated fat...

'She fed them bad fats -
saturated fats,

'and good fats -
monounsaturated fats.

'She did the same
with carbohydrates,

'feeding people low and high GI,
whole grains and refined grains.'

Maybe is about the fibre in the food
or maybe is about sugar.

'For ten years,

'she conducted a series of detailed
scientific studies

'into which was worst -
fat or sugar.'

So I'm on tenterhooks, like,
so what did you find?

You know, the changes
that we got were important,

but they were quite modest.

They were surprisingly small, much
smaller than I was anticipating.

And there are clear benefits

of a little bit more
monounsaturated fats,

some benefits of low GI,
some of more fibre,

but I really don't think
we could say that a diet

which had some extreme composition
was really a revolutionary answer.

What her study showed was that
changing fat or sugar on their own

had a very small effect.

Especially when compared to the
effect of losing or gaining weight.

So what is it that we're eating

that's making us fatter
and unhealthier?

Unlikely as it may seem, the first
clue in solving that puzzle

might lie in this tempting
tray of doughnuts.

What I want you to do is look
at this tray of doughnuts

and think about which one you'd
choose if you could have any of them.

Got it?

Now, this is like a card trick,

I want you to remember the doughnut
you chose and we're going to see

if the people in New York
choose the same one as you.

All you have to do
is choose a doughnut.

Ah, it's easy.

I'm going to find out
if people in London

have the same taste in doughnuts
as people in New York.

Right, do you want a free doughnut?

Er...I would like this one.

The same one. Yeah, yeah, yeah.

So can I offer you a doughnut?

Yeah, go for it, go for it, yes!

I'm on a diet.

XAND LAUGHS

Is that good? Yeah, it's good.

Everyone pick a doughnut.

That's my favourite one. Is it?
It's my favourite one as well.

You said that was your
favourite one, why?

Just cos I've tried practically
all of them

and I just like this one.

Guys, thank you very much.
Thank you! Enjoy your day!

So it's really interesting -
all the glazed doughnuts have gone,

only one person picked
the chocolate one.

Everyone seems to be going
for the glazed ring.

Let's see if that continues.

'So why is that? What's so special
about this particular doughnut?

'The doughnut preferences
of Londoners and New Yorkers

'is in fact a clue to what we think
is some of the most intriguing

'new science in nutrition.

'The real work is being done with
rats and what they like eating.

'Everyday rodents who work
with Professor Paul Kenny,

'a world-renowned researcher
in the neurobiology of obesity

'and, rather interestingly,
addiction.

'He devised a series of elegant
experiments to work out

'what foods we like and why.

'The first thing he did
was feed his rats sugar.

'And they could have as much
as they wanted.'

The animals, of course, enjoy
them and they'll consume vigorously,

but they tend not to gain weight,
because what they do is

they adjust the consumption of other
macronutrients to compensate.

So, on average, animals with access
to high-sugar solutions

consumed the same amount of calories
each day as they would

if they weren't having access
to those solutions.

Really? So if you let a rat drink
all the soda it wants to,

or you let it have unlimited access
to sugar, it doesn't get fat?

Typically, no.

'Then, he gave them as much fatty
food as they wanted.'

If you just give them access to fat,

they will gain some weight,
but really not that much,

and what you find is they don't eat
as much, physically eat as much

food as they would've before,
the reason being

that they know that the fat
is high in calories

and their body is quick
to deal with that.

They have signals that tell them,
"You've had enough, stop eating."

'And there's something simple
you can do at home to get

'a sense of what Professor Kenny's
been studying.'

This is double cream and it's thick,

it's luxurious, it's rich,

it's creamy...

..and it's really boring.

This is sugar.

After even with one mouthful,
it's overpowering.

BUT if we mix them together...

Now, that stuff I could eat all day,

and in fact, we do eat this
all the time,

cos basically, what we've just made
is ice cream.

Now, this ice cream is absolutely
delicious and the reason it tastes

so good is because the combination
of fat and sugar is unbelievable.

Mm.

So, Professor Kenny
took this simple insight

and fed his rats foods that were
high in fat and sugar.

So what happened when
you fed cheesecake to rats?

They practically stopped eating
the regular, healthy food that

was there, but they didn't binge
on the high fat, high sugar stuff,

they grazed on it, but that
was their main source of calories.

This is the going to the fridge
and just having a spoonful

of ice cream every 20 minutes.
Precisely, yeah.

You know, you get up and you eat,
but if you're going to eat

it's for that type of food and you
tend to eat much more frequently.

You're not gorging on it, but
that's what you eat continuously.

And those animals gained
a massive amount of weight,

they really gained a lot of weight,
and they became sedentary.

They slept a lot,
didn't move around,

but that was where they got
their calories from.

What Professor Kenny's
discovered is that,

unlike fat and sugar on their own,

the rats had no off switch when it
came to fat and sugar combined.

The combination of fat and sugar
is completely different

than either macronutrient alone,
and it tastes remarkably good.

And so what you have are these
systems in the brain that are there

to respond to not whether
you need food to live,

but whether you like using food,

and they're engaged,
they're called hedonic systems.

It's much like what happens
with drug addiction.

You don't need heroin,
you don't need cocaine,

it's got no nutrient value,
it's got no caloric value,

it doesn't do anything for you
except make you feel good.

And it's exactly those hedonic
systems in the brain that we think

are being impacted far more
when you consume food

that's rich in fat and sugar, than
consuming either sugar or fat alone.

When you think about it,
we all know we need to eat to live.

But what Professor Kenny's
discovered is that the combination

of fat and sugar supercharges
the brain's reward system,

overpowering its ability
to tell us to stop eating.

And it's a manufactured combination,

you can't find it
anywhere else in nature.

But here's what's
even more remarkable.

He's discovered that his rats
didn't just like

a mixture of fat and sugar,

the ratio of fat to sugar was
crucial to how much they liked it.

When I looked at the composition
of cheesecake and I was surprised.

It had a highest percentage of fat
of any food item

that we looked at
that wasn't actually pure fat,

and it had remarkably
high levels of sugar. So it was

the combination... What's the ratio
of fat and sugar in cheesecake?

It's pretty much 50/50. Really?

It's about a half fat
and the rest of it sugar

with various other things to keep
the whole product together.

OK. So it's basically
half fat and half sugar.

Chaps, can I offer you doughnuts?

OK, there you go, go for it.

I like these ones.
Tuck in, there's no trick.

Now remember, the most popular
doughnut was this one,

the glazed ring,

and there's something really
special about this doughnut,

it's got an exactly 50/50
mixture of fat and sugar.

The pink one,
that's got extra sugar on the top,

and this one is filled with cream.

So there's no question,

we absolutely love this
combination of fat and sugar.

It's no surprise that people
liked this doughnut.

It tends to be the bestseller
on both sides of the Atlantic.

The fact that the world is getting
fatter is a new phenomenon,

and what seems to be driving it,

at least according to Professor
Kenny, is processed food,

because that's where you find
this deadly combination

of fat and sugar that you don't
find anywhere else in nature.

And what this does
is it fundamentally interferes

with our mechanisms
of self-regulation and reward.

It seems that it's
fat and sugar together,

not fat or sugar alone,
that's the real problem.

And Chris wanted to find out
from Professor Jebb what
we could do about it.

When people tell me
they crave sugar,

I say, "What, sugar
out of the sugar bowl?

"Oh, no, no, no." Or fat,
pats of butter? Generally not.

What people really seem to desire,
whether that's physiological

or whether it's a learnt behaviour
is these fat/sugar combinations.

They are very energy dense,
so they pack the calories in,

and they are unbelievably
pleasurable and attractive.

Are these temptations
for you as well?

Oh, I think they're
temptations for most of us.

One of the things that I often say

is it's astonishing
that any of us stay slim.

In a world like this
where in Britain we are surrounded

by pretty delicious, relatively
affordable, palatable foods,

actually you have to exert quite
a level of dietary restraint

if you're not going to effectively
just sleep-walk into obesity.

So I want your top tip,

a basic rule, like my go to
thing when I'm feeling weak.

By making some pretty modest
changes, but right across your diet.

Certainly cutting out some of those
kind of discretionary

treat type foods
which are no longer really treats,

they've become everyday items.
Yes.

If you take those out
you can cut calories

and you can cut lots of those
other nutrients of concern.

So you end up with a healthier diet

and one on which you can also
lose some weight.

And I think that really is
the secret to developing

a much more
holistic attitude to food,

which doesn't sort of believe
that any one item is a saviour

or a sinner, it is about
the overall balance of the diet.

We've all heard that before

but the difference is
that we now know our enemy.

It's not fat.

And it's not sugar.

But the deadly, addictive,

delicious mixture
of fat and sugar combined.

What's amazing to me
about all this is that

I've been a doctor for ten years,

I've spent six years
at medical school,

and I thought I knew a lot of
this stuff and I just didn't,

like I was wrong about
a lot of stuff.

So basically what
I get out of this is

I have to avoid the processed food,
the doughnuts, the ice cream,

the cheesecake, that sort of 50/50
fat/sugar mixture

I cannot stop eating, and it's...
and that's the problem.

So I'm going to cut those out
completely.

So that where I end up
is going all faddish diets,

all faddish diets,
are wrong and misguided,

all of them. Yeah.

And doing exercise
is really important.

You need to keep the muscle
because muscle is an endocrine organ

that affects your whole metabolism.

So, in the end, as doctors,
we'd love to be able to give

one simple rule or give you a pill
that would fix all this,

but in the end we can't.

It's up to you.
It's up to YOU.

All right, it's up to...
It's up to you too.