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 diaries 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 effect 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 the effect of these 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 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.