The Truth About... s01e03 Episode Script


Doughnuts, ã1 each now.
Fat - it's in all the food we love to eat.
'There's nothing that tastes quite so good.
' I could ad-lib on cheese forever.
'But it's a love-hate relationship.
' It's naughty, cos it's all fried.
'We're terrified about what it does to our bodies and our health.
' Fat has a reputation of being public health enemy number one, but is it really as terrible as we've come to believe? 'I'm Saleyha Ahsan and I'm a doctor, 'but I've got more than a professional interest in fat, 'because I've discovered I'm carrying far more 'than is good for me.
' I'm nearly double what I should be.
'So I'm on a mission to find out 'whether fat is really the devil it seems.
'I'm going to look into the very latest science 'and uncover some surprises.
' That's pretty amazing.
'I'll find out which saturated fats might be good for us after all, 'reveal the shortcut to burning fat long after we stop exercising' Off you go.
and discover the strange fat that might be added 'to the food of the future to make us healthier.
' It's It's really salty.
I think we can be smarter about fat, both in our food and in our bodies.
It's time to discover the truth about fat.
'As a nation, we're utterly confused about fat.
'And I see that confusion wherever I go.
'Take the weird new fad hitting our coffee shops, 'where a nice hot brew 'now comes with a big lump of butter.
' When I first heard about this coffee, I couldn't believe it, BUT I won't judge it until I've actually tried it.
'It looks like a heart attack in a cup.
'Coffee, butter 'and a shot of palm and coconut oil, for good measure.
'The idea is it's supposed to keep your energy levels up for hours.
' I normally only ever have a weak white coffee, so I'm really interested to see the effects of this dollop of butter.
In fact, two dollops.
Thank you, thank you.
This just doesn't feel right.
For decades, we've been told to avoid saturated fat to stay healthy.
And in here, it's something like my entire day's allowance, so it better be worth it.
Let me give it a go.
Eurgh, right.
I'm meant to be a bit more diplomatic but I can't lie! Cos, I mean, it tastes like coffee .
but you've just got to be prepared for that funny, oily sensation on your lips.
I think the reason why people are throwing caution to the wind and dolloping their butter into their coffee is because of headlines like this.
'Over the last few years, we've seen reports that suggest 'we've got it wrong about fat, 'that it isn't as bad as we think, 'and that even the worst offender, 'saturated fat, 'might actually be good for us.
'So, what should we believe?' It's so complicated, and even for me as a doctor, I find it challenging.
'So, to clear up all this confusion, 'I'm going to dig into the very latest science about fat.
' 'First, I've come to Aberdeen.
'We've taken over a country house outside the city 'and brought in a group of volunteers.
'We're going to put them through a unique set of experiments 'all involving fat.
'They won't find it easy.
'In fact, they're in for a few shocks.
'But it will help us find out 'whether fat is really bad for us, 'or good for us.
' Hello.
'Like me, our volunteers are bamboozled 'by all the different things they hear about fat.
' I think it's confusing because there are so many different fats.
Yeah, definitely, cos you get stuff that's, like, reduced fat and low fat, and zero fat, and actually, something that's reduced fat still has a lot of fat in it.
You're nodding in agreement, Daisy, what do you think? I think we all want to be healthy, but there's a lot of mixed messages out there.
The best way would be to simplify things so people just know this is wrong, this is right.
I tend just to look at foods and not obsess about the fat content in them.
There's so much in magazines now about which latest celebrity is following which diet, no carbs, no fat.
It's really confusing.
Perhaps the confusion starts with the word "fat" itself.
It can mean more than one thing.
The fat on our plate or the fat in our bodies.
So the question is, when we eat fat, what happens inside us? 'To find out, we've served up four very different meals 'for four of our volunteers.
'A pizza topped with cheese that's full of dairy fat, 'a salad of avocado and salmon and oily fish, 'a greasy burger and chips, 'and a small bowl of nuts, 'rich in natural fats.
' Could you honestly eat pizza for your breakfast? No.
That's quite continental.
Burger and chips, though.
That's a good way to start the day.
'It's the first thing they've eaten in 12 hours.
' Right, guys.
ALL: Hi.
Lots of food in front of you all.
I know you've not eaten since last night because we're going to do some tests on you.
So, I'm not going to hold you up.
Tuck in, bon appetit.
ALL: Thank you.
I'm fair chuffed with my salmon, it's lovely.
'All these foods contain fat, but they're obviously different.
'So I want to know which of them puts the most fat into our bodies.
'To find out, we're taking a blood sample from each volunteer.
' Sharp scratch, there we go.
'Dr Emilie Combet is an expert in nutrition 'from Glasgow University.
'She's going to test how much fat is in their blood 'before and after they've eaten their meal.
' What we have here are your blood tests.
So, what we did, we took your blood before your meal and after the meal, so several time points.
And that's a normal sample of blood.
So, you see, it's red, it's healthy, and what we do with those blood tubes, we put them in the centrifuge and that's a machine that is going to spin those tubes very fast.
And what we obtain at the end is a sample like that.
And what we can see, at the bottom, we've got our red blood cells.
And on top, we've got this yellow, clear layer, which is plasma.
So, your blood would look like that in the morning when you haven't eaten, for example.
'Now to see how the different fatty meals 'have affected our volunteers' blood.
' So, which one of the meals did you think had the most fat in them? I think what I had, the burger and chips, might have been the most fatty.
Yours, yeah? Your burger and chips? I think it would be the burger and chips.
Let's have a look at the blood after having eaten a burger and chips.
Well, here it is.
What do you think, Dave? Well, it's a lot more cloudy, isn't it? Uh-huh, the cloudiness comes from that fat, the fat has gone into your blood.
So the actual cloudiness that we're seeing here is the fat that Dave ate.
That fat passed into his blood and creates the cloudiness, exactly.
It doesn't make me want to eat a burger and chips again, very soon.
'So after Dave's burger and chips, 'his blood is cloudy with fat.
'But how much fat did the others get 'from the healthier looking nuts or salmon? 'They're hoping their samples won't look so cloudy.
' I bet you're all dying to find out.
What do you think? They're not looking good.
But the big surprise is that all your samples are cloudy.
I think a lot of people would be quite shocked, actually, that the fat that you've eaten has gone so quickly and so directly into your bloodstream.
And in fact, when we eat the food, the fat is almost entirely absorbed by the blood.
95% goes into the blood.
'So, whether it's a healthy salmon salad 'or a greasy burger and chips, 'every bit of fat we eat ends up in our blood.
'Our bodies are built to squeeze all the fat 'from every different food we put in our mouth.
'But where it starts to get really interesting 'is what happens next.
' 'It's often said that fat goes straight from our lips to our hips, 'but the truth about what happens to the fat in our body 'is far more interesting.
'And to show you, I'm going to use myself.
' OK, so it's now time to talk about my weight.
Over the last few years, I've been getting fatter.
I used to do a lot of running, but I've now got an ankle injury, but I haven't changed the way that I'm eating.
So as a consequence, there's rather more of me here today than there was before.
'I want to see just how much fat is in my body and where it is, 'so I'm having an MRI scan.
' We scan you from the top of your head, all the way to your feet.
I think it's going to be a real "mirror, mirror on the wall" moment, "who's the fattest of them all?" Well, it'll be a good measurement of how much fat you have and the distribution of that fat.
So, all this white bit here is all your fat around your body.
It's quite something, actually, to see your own body right from the inside.
'The first kind of fat I can see is a thick layer all around my body, 'just under the skin.
' Oh, my God! Got it right around my hips.
'That's the stuff I can pinch 'and I can see I've got far too much of it.
' I'm really not doing myself any favours, at all.
'But that's not the only place we've got fat in our body.
'Now Jimmy shows me a different view from the scan.
' So, we're looking from the top 'Looking straight down from the top, this is my abdomen, 'where my organs are, and all that white stuff around themis fat.
' Oh, my God, that's pretty revolting.
As you can see, your organs are literally kind of surrounded, embedded within the internal fat.
It's like they are in a sea of fat.
I just find that, just really horrible.
Really awful.
OK, so your percentage body fat is 43%.
And what's the normal? Between 20% and 22%.
I'm nearly double what I should be? It is something that you have to be concerned about Yeah, absolutely.
I think it's the thought of having fat in my liver that just fills me with dread, actually, cos that's really not healthy at all.
'Too much fat within our tummies 'is more dangerous than too much under the skin.
'It can lead to diabetes and heart disease.
' Seeing the way that fat is coating nearly all of my organs This is a huge wake-up call for me.
It's almost enough to put me off eating fatty food ever again.
And yet, I also know that in a healthy diet around a third of the calories we eat should come from fat.
It's crucial stuff.
And to show you why it's so important, we're about to ask our volunteers to do something extraordinary.
So, what I'd really like to do is to ask you to step away from the fat, to give it up for a whole week.
So that's seven days, no fat.
Who's up for it? Yeah, that's OK.
Yeah, bring it on, I like a challenge.
As a scientist, I know that often the best way to understand what something is doing is to take it away.
So we're going to strip all the fat out of our volunteers' diet to see how it affects their body and mind.
It's a bold and challenging thing we're asking our volunteers to do.
Overdoing the fat's easy, as many of us know, but underdoing it, now that's another story.
Very few of us have experienced that.
They're going to find it tough.
I know I love crisps and I would eat six bags, one after the other, if I could.
I think it's going to be tough for me to not have that kind of go-to pick-me-up, but I think the hard part as well is going to be how to make a meal.
I'm obviously a girl who loves her food, so it's going to be interesting to see how having zero fat for a week is going to be.
I think it'll be hard.
I do think it will be hard.
Going to have to be quite strict with myself.
But what our volunteers don't yet realise is that this will be a test of far more than their willpower.
The latest science suggests that living without fat will affect their body and mind in unexpected ways - some of them weird, some of them frankly rather unpleasant.
So they've all had to have medical checks and be cleared to take part.
'The first question is - what CAN they eat? 'We need to hunt down the everyday foods with the least fat.
' OK, team, what I want you to do is arrange these foods in order of fat content with what you think is 0% at this end and what you think is over 50% at that end and then everything in between.
Ready? Off you go.
Shall we do the extremes first, the low-fat and high-fat? Yeah, it might be easier.
This'll be high They're going to be high, aren't they? Everything I want to eat is going to be up there.
Will we take the butter up here as well? That's the turkey, that probably needs to go down 'Keeping an eye on our volunteers is dietician Lucy Jones.
' No, I think it will be this lot.
Yeah, maybe sort of 5% or so So, Lucy, cutting out fat from your diet is actually easier said than done, isn't it? It really is and what we're about to find out is that fat is present in so many different foods, ones we don't even think about, so trying to adopt a diet that's basically fat-free is incredibly difficult in practice.
Between one and five? I think it will be lower than that.
Yeah, I think only maybe one, or 'Very few foods contain no fat at all.
'Almost everything is a mixture of protein, carbohydrate and fat - 'the three basic building blocks of a healthy diet.
'Even vegetables contain a bit of fat, 'so to make sure our volunteers have something to eat this week, 'we're allowing them anything with less than 1% fat.
' They're yummy sweeties.
They must be up here.
No, I don't think so, cos these are, like, just sugar-based.
It's all sugar, isn't it? If you cut out fat, what's going to happen to them? Well, that's going to be one of the really interesting things to watch Oh, what about this? .
because they're going to be quite restricted in terms of what they can eat, and I think that means through a day, they're going to end up eating less.
So it'll be quite interesting how hungry they get in the week.
Anything we need to change? Very little in the middle.
Looks about right for down there.
Last change? Last change.
Guys - confident, happy? ALL: Yeah.
No more changes? No.
Right, OK.
There are a couple of quite shocking surprises.
Now, these cream crackers are actually around here.
That's way down, that's past the 10%.
That's right, so they're about 13% fat, cream crackers.
Wow, even more than our Jaffas? Yes, actually, the Jaffa Cakes are in the wrong position.
They only need to move to about here, about 8%.
The nuts, which you guys have placed at around 10% - 50% fat.
What?! It's neck and neck with the butter.
It's not neck and neck with the butter.
Oh, is it not? So the butter should be actually over here! Off the table, off the table.
So, the butter's around 80%.
An avocado - super healthy, full of monounsaturated fats.
They're actually slightly higher in fat than the sausage rolls.
What about the cereals? Yeah, cornflakes actually have about 0.
9% fat, so they'd be right down here with the allowed foods Wow.
where the wheat-based cereal has about 2% because it is whole-wheat.
So, cornflakes is in, guys, tons of these.
Yeah, I'm quite happy about that.
Who wants one? ALL LAUGH I think the sweets being allowed in your week just help to clarify that this isn't necessarily about health, this is just about getting the fat out of your diet and seeing the effects of that.
So, now, our volunteers are off for their first fat-free shop.
They can choose what they want so long as it's below the magic 1% fat.
Those are 1.
7, so I can't have those.
Their weird regime for the week could include fat-free dairy, like yoghurt and skimmed milk, lentils, beans and pulses, or sweets and jelly.
Cornflakes are on the menu, but wholegrain cereal is not Oh, too much.
owing to the oily wheat germ in it.
No, not even them.
And surprisingly, bread is out too.
Chicken breast is off limits, as are most meats.
But some lean fish will be fine.
Actually, Quorn meatballs soundsOK.
The weekly shop has become a bit of a nightmare.
No meatballs for me.
Quite interesting to shop hungry and know that you couldn't buy any fatty foods at the same time.
I've got rice vermicelli.
A few onions, carrot, lentil and orange soup.
I went and I bought sweeties just because I knew I could! SHE GASPS "Fat - nil.
" I don't know how easy it's going to be to do this this week because I was really surprised there's fat in porridge.
We're going to monitor our volunteers through the week to see how cutting fat out completely affects their body and mind.
It would be fair to have described that as a joyless experience.
'One of their first surprises will be what happens in their mouth.
' 'Dr Andy Connelly is a chemist with a fascination for food.
' Hello, Andy.
'He wants to show me some of the hidden powers of fat.
' 'First up, two glasses of milk.
'One full-fat, one skimmed and fat-free.
'Add a dash of vanilla extract to each.
' Give 'em a bit of a stir just to mix it in.
We'll start with the skimmed milk.
It smells vanilla-y.
And it doesn't taste great at all.
It tastes like medicine.
Yuck! It doesn't taste like vanilla.
Try the full-fat one and see what the difference is.
That That tastes like vanilla.
That tastes like some sort of milkshake.
Yes, it's much more pleasant and it's all because the fats affect the transfer of flavour into your mouth.
'In the full-cream milk on the right, 'droplets of fat soak up the vanilla flavour like a sponge 'and release it quite gradually when I taste it.
'In the skimmed milk, where there's no fat, 'the flavour is released much more suddenly.
' So, in the warmth of your mouth, suddenly you've got this flavour that isn't quite right because it hits you so quickly.
Whereas when you've got the fat, it goes into your mouth and cos it's a sponge, it releases the flavour, but only slowly.
So it fills your mouth, it's much more pleasant.
And also, milk is very thick, so it coats the inside of your mouth and the flavours stay in your mouth much longer, and it's a much more pleasant experience.
That's just so unbelievable.
I would never have guessed that.
I can't believe how weird that tastes, it's gross! It's so gross.
So gross, I'm going to try it again.
HE CHUCKLES Rather you than me.
Cos it just, it's so bizarre.
Yuck! Isn't that clever? That's really clever.
Clever old milk.
It is, amazing, yeah, yeah.
'So, fat really affects the way food tastes, 'altering how flavours are released and linger in our mouth.
'But there's another way fat can change food.
' It's been absolutely ages since I've made chips.
Yeah, me too, me too.
But I'm tempted to start doing it again.
SHE LAUGHS 'When we fry food, we create a special kind of crispiness.
' They actually look ready.
They look lovely and brown, just ready to eat.
'A crispiness that's almost impossible to achieve 'any other way.
' OK, I'm going to go for That's quite a crispy one.
That's really nice.
So, they're quite brown and crispy-looking on the outside and on the inside fluffy and soft, why is that? Well, it's all down to the difference between fat and water.
When we cook with water, we cook at the boiling point, about 100 degrees.
In fact, we go up to 180, 190 degrees.
That's almost twice.
Exactly, yeah.
So when we lower it in, you can hear .
all that water boiling away from the surface of the potato.
So, that bubbling is actually water coming off the potato? Exactly, yeah.
It's the steam coming off the surface of the potato, drying it out and making it really nice and crisp.
'The hot oil dries out the surface of the potato in seconds, 'much quicker than any other way of cooking.
'And this creates the crispy coating around a soft, squishy inside, 'that makes the perfect chip.
'And there's something else the oil is doing.
' What's also happening at these really high temperatures is there's all sorts of reactions happening on the surface of the potato, making it brown, and creating loads of fantastic flavours that make chips taste so great.
'So the reason we love fat so much starts in our mouth, 'thanks to the textures and flavours it can create.
'But it's what happens next that shows just why fat 'has such a powerful hold over us.
' It has recently been discovered that from the instant we put something fatty in our mouth, surprising things begin to happen in our brain.
And our brain is where fat really exerts its hidden power over our lives.
To show me, Dr Fabian Grabenhorst has a bizarre-looking experiment.
What you have here is different types of milkshakes, which differ in their fat content.
So some are fatty, others are not so fatty, and these are computer-controlled juice pumps, which can pump the liquid through these tubes, straight into your mouth.
OK, and it's rigged up to this computer? Right.
Every time you taste a liquid, it can tell us how much you liked it and how fatty you thought the liquid was.
OK, cool.
Should we give it a go? I think so.
'Without knowing which is which, I have to score the milkshakes 'by how much I like them.
' Oh, I didn't like that one.
That tastes a bit like medicine.
Do you want to have another go? Yeah.
'And, you guessed it - it turns out I like the fattier ones most.
' 'Fabian ran this test on a bigger group of people 'and scanned their brains at the same time.
'And he saw something remarkable.
'Within half a second of the higher-fat milkshake 'touching their tongue, their brains reacted to it.
' So these signals come in from the tongue and this part of the brain detects whether there's fat in the mouth.
'Then, he saw a second response, 'this time in a deeper part of the brain that registers pleasure.
' It's an interesting part of the brain because it's often associated with emotional processing and sometimes it's also associated specifically with unconscious processing.
It seems we're "hard-wired" to love fat.
In prehistoric times, this could have helped us survive, driving us to hunt down fatty foods to keep us going when food was scarce.
Today, we still have an in-built urge to seek out fat and this makes it hard for us to resist.
When we give in to temptation, perhaps it's not so much a lack of willpower as a powerful, primitive impulse.
And if we're completely deprived of fat, we soon begin to struggle, as our volunteers are finding out.
Eating no fat I don't think it's annoying, but it's It's not exciting.
I've managed to have jelly and some fruit for breakfast, which certainly isn't a combination that I would normally choose to have for breakfast.
It's gooey, mushy The food's ratheruninspiring.
As the week goes on, will they find it easier as they get into the swing of it? I think they are going to find knowing what foods to eat easier because they'll get used to the types of foods that they are safe to consume in the first couple of days.
But aspects of it are just going to get more and more difficult as the week goes on.
They're going to start to feel hungrier, they're going to get bored, and also, because without fat in their diet, they're going to be eating more of things like carbohydrates, which could possibly be giving them peaks and troughs in their blood glucose levels, giving them surges of hunger and dips in energy levels.
When I eat loads of carbs, I end up feeling really bloated.
Will they have that as well? There is a group of carbohydrates that we don't break down very well and they actually ferment in our large bowel and produce gas, and that gives people sort of crampy, painful feelings.
So, things like beans, pulses, wheat lots of different fruits and vegetables, and if they suddenly start eating much more of those types of foods than they would normally, the chances are they could get some tummy symptoms.
I haven't felt hungry, but I have felt bloated today, which Ihaven't enjoyed in the slightest.
I've got a really, really sore tummy, I'm very bloated.
I do miss cooking with oil.
Congee noodle stir-fry.
I'm starving, so I'll eat it anyway, even if it is disgusting.
But, of course, most of the time, we're free to eat as much fat as we like and it's all too easy to overdo it.
What's not so easy is to burn the fat off again, as I know full well myself.
'Now, as a doctor and as someone who's overweight, 'I'm a bit obsessed by how we burn fat.
'Exercise is a key part of it, 'but there's some exciting research in this area that might offer 'the less keen amongst us a smarter way to do it.
'First, I need to find out how much fat my body is burning 'when I do something simple like walking.
' This mask is measuring what I breathe in and what I breathe out, and it's sending it all to a computer, and we'll analyse that later.
'Now, I've always thought sugar and other carbs 'are the first source of energy our body draws upon.
'So I'm not sure if my walk is really burning any fat that all.
'Sport scientist Dr Jacky Forsyth is crunching 'the numbers to find out.
' Well, it shows you've been using quite a lot of fat, so approximately 64% of your energy is coming from fat.
That's your proportion of fat you are using, so there was that much fat and the rest you are using of carbohydrate and we can convert that into grams for a whole hour.
Go on, then.
Tell me.
Approximately, you were using about 27 grams of fat, which is fairly substantial.
You know, you could eat a nice burger with that.
That's amazing! Quite good, isn't it? That's massive.
That is huge.
'So it's easier to burn fat than I thought.
'Trouble is, as soon as I stop walking, 'the fat-burn drops off too, so Jacky's going to show me 'a trick that'll keep it going - even when I'm not exercising.
'Lou and Dean are going to demonstrate how to turn your body 'into an amazing fat-burning machine in three simple steps.
' That's good.
This is excellent.
'Step one.
Exercise hard for just two minutes.
' Keep it going.
'Step two.
Rest for one minute.
'Step three.
Repeat seven times in total.
' Keep going.
You're doing really well.
Keep going.
'Just 20 minutes later, that's it.
'The idea is that this pattern of exercise 'and rest actually makes our body burn more fat for hours afterwards.
'To see if it worked, we've tested Lou and Dean before and after.
' Before they started exercising, they were burning this amount of fat and then afterwards, they almost double the amount of fat they were burning and this was two and a half hours after they'd stopped exercising.
It even can go on for 24 hours after you've finished exercising, so you'll carry on burning that fat.
That's actually a massive incentive.
So you keep having the effect of the exercise long after you've stopped? Yeah.
It's not always twice as much but from the short experiment we did, we saw that happen.
'I'm genuinely amazed it's possible to double the fat we're burning 'with just 20 minutes of exercise and rest.
'But could this ever work on someone less fit like me?' Do you have to be as fit as Lou and Dean to get same effect? No, I think as long as you push yourself proportionally to how you feel, then that's fine and what we tried to get Lou and Dean to work at was an exercise intensity that they could describe as being really hard.
Now you can get that same benefit if you're not so fit but you do have to be prepared to push yourself.
So whatever your fitness, the key is to push yourself to your own limits.
Even if you're a bit out of shape, a regular stride up a steep hill with a quick rest every two minutes could increase your fat-burn long after you've finished.
A lot of gain for not much pain.
So I've learned it's easier than I thought to burn fat.
I don't eat a huge amount of fatty food, yet I've still got way too much fat in my body, so I want to get to the bottom of why that is.
What exactly is it that makes us fat? To find out, I've come back to medical school to take a closer look at fat.
Right, James.
This looks familiar.
What I'm looking at is some body fat.
It is.
The almost bright yellow parts of this tissue - that's fat.
Fat is quite essential to us, actually, isn't it? Absolutely.
It cushions the vital organs from injury.
It makes sitting down comfortable.
If you were to sit down on a hard plastic chair without fat tissue around your bum, it would be very, very painful.
But most importantly, our body fat acts as a store of energy.
So as long as you've had water and vitamins, you could keep going on the energy that's stored inside your body for around 60 days.
60 days with no food? Up to 60 days for a normal person.
And how many Mars Bars is that? That's well over 600 Mars Bars.
Crikey! If that sounds like a lot, anyone who's overweight is carrying even more body fat.
And to find out why, I'm going to look deeper into the secret world of fat.
So, James, we're looking at fat under the microscope.
We are.
This is a slide of human fat cells and within that fat cell, you can see a collection of droplets of oil.
Gosh! So each one of these cells is like a little fuel tank of energy.
Yes, that's quite a good analogy.
It provides us with energy for periods when you're not eating any food.
So if you eat too much fat, you will grow fat? You certainly can grow fat from eating too much.
But if you eat too much carbohydrates as well, then you will grow fat.
So what you're saying, sugar Yeah.
Carbohydrates Becomes fat.
Become fat.
And they end up looking like that? Looking just like that.
So our own bodies actually make fat.
If we eat too much of anything, like sugar and other carbs, it gets changed into fat and stored in cells like these.
And what's really astonishing is that these fat cells do something no other cell in our body can.
The more we eat, the bigger they grow.
If you take the average fat cell, it can increase in volume by a thousandfold.
So it can go from being relatively small to being 1,000 times bigger.
It's like a party balloon.
Oh! So more obese people have bigger cells of fat.
They generally have larger fat cells.
So the truth is, simply EATING fat isn't the true reason we get fat.
The real problem is eating too much, whether that's fat, sugar or anything else.
For our volunteers, the effects of living without fat are getting harder to bear by the day.
All day I've wanted to eat something that I'm not allowed.
I am definitely hungry.
I don't have a lot of energy.
Today so far, just sleepy and bad-tempered.
I'm quite sad to know today that turmeric has fat in it.
I'm hungry when I go to bed, I'm hungry when I get up.
My tummy is just constantly rumbling.
I feel like I could eat a scabby horse right now.
My bowels are not working properly, so I'm a bit, um It's been a long time since I went, just let's say.
Going fat-free, they are tired, hungry, moody, and having some rather unpleasant tummy symptoms.
I'm beginning to appreciate just why we need fat.
But exactly which fats are good for us and which are bad? Of all the questions about fat, I think it's the one that causes most confusion.
Look at all of these oils and fats.
There are so many and I want to get to the truth.
So we've collected some of the bewildering array of fats we Brits load into our shopping baskets.
Some of them come in liquid form as oils.
Our supermarkets sell nearly 60 million litres of basic vegetable oil a year, then there's the solid fats like lard.
We buy over 15 million kilos of the stuff.
Why are some fats good and some fats bad? Well, as with anything in nutrition, it's never quite as black and white as we'd like it to be but we do know that in the UK, people tend to have too much saturated fat in their diet.
So the ones that are at the front that are solid at room temperature have a higher proportion of saturates.
So all these ones at the front, the solid fats, are not as good for us as liquid ones? Generally speaking, that's the case and there is a link with having too much saturated fats and a rise in your blood cholesterol.
Unhealthy levels of cholesterol are bad news because they've been linked to an increased risk of heart disease.
That's why, over the years, we've seen so much bad press about saturated fat, but is unsaturated fat really any better? Unsaturated fat almost has the reverse happen, whereby it helps to lower your bad cholesterol in your blood and actually can be cardioprotective and help to protect your heart against heart disease.
So, used in moderation, some oils can be good for our hearts.
Extra virgin olive oil is the one most of us know about.
Rapeseed oil is another popular choice.
And you can often save a bit of money by buying it as a bog-standard vegetable oil.
Check the label, but it's often rapeseed, and costs a lot less.
People get really confused about what oil they should pick, but actually, most of these have the majority of their fats as unsaturates which, generally speaking, are better for our heart health and cholesterol.
So there does seem to be a general rule that unsaturated fat is better for us than saturated.
Broadly speaking, that may be true, but recently, the picture has become far more confusing.
For decades, saturated fat has been thought of as the ultimate baddie, the fat we should cut back on.
But recent headlines have suggested it might not be as bad for us as we think.
Sensational stories like this seem to contradict decades of health advice, telling us to avoid saturates.
And they claim to be based on the latest science.
No wonder we're baffled.
So, to get to the truth, I've got a rare chance to speak to one of the scientists whose work has inspired some of the headlines, Dr Nita Forouhi.
This hi-tech lab is on the front line in identifying the good, the bad and the ugly of the fat world.
And the results are exciting.
We are now beginning to understand that, actually, saturated fat may not be all the same.
We tend to think of all saturated fat as one homogenous lump.
But actually, saturated fats are made up of lots and lots of different saturated fatty acids.
Different foods contain a rich mixture of many types of saturated fatty acids, and they could have different health effects.
So different foods contain different saturated fatty acids.
To try and find out which is good and bad for us, Nita's team have done some scientific time travel.
12 years ago, blood samples were taken from thousands of people and frozen.
Now, the team can identify which fatty acids were in that blood and look at the health of the same people today.
That's quite remarkable.
So that's like a snapshot of someone 12 years ago, their diet and what was going on in their body at that time, and we fast-forward to today and we see where that person is now, what diseases they have, look at the blood samples and see what their links are.
Yes, you've got it absolutely right.
What Nita wanted to investigate was the link between saturated fatty acids and diabetes.
It's early days, but her results are a bit of a shock.
What we found is that there were some individual saturated fatty acids that were related with a higher risk of diabetes.
But there were other fatty acids that were associated with a reduced risk of diabetes.
So, depending on the type of saturated fatty acids people had in their blood, they are at differing risks of developing diabetes.
Yes, so the two particular fatty acids that were related with a reduced risk of diabetes are well known to come from dairy products.
Nita's study isn't the only one to suggest a link between some of the fatty acids in dairy and benefits to our health.
Other studies have linked one of the fatty acids to a lower risk of heart disease.
Could it be that dairy fat is about to redeem its reputation? Well, there's a lot of consistent research coming out that dairy products, in fact, have beneficial health effects.
And processed meats have adverse affects for health.
So the picture isn't black and white.
Saturated fats don't appear to be all bad or good, as the health headlines sometimes claim.
The latest science suggests that some fatty acids in dairy might be good for us, whilst those in processed meats like sausage, bacon and pies might be bad for us.
It's early days for this research.
Finding promising links isn't the same as proving a direct cause and effect.
And that's the next stage for Nita.
We cannot prove a causal cause-effect relationship here.
But that's the next step and we certainly have plans to investigate that further.
This is fascinating.
But I'm not ready to change my advice or do anything radically different myself.
But a bit of cheese or yoghurt might turn out to be good for us in ways we didn't realise.
There is one sort of fat that really does have star status.
You've probably heard of it, although you might not have realised it was a fat at all - omega-3.
Omega-3 helps build the cells of our body and it's a key component of the grey matter of our brains.
There's evidence it protects against heart disease and even possibly stroke and dementia.
Omega-3 definitely sits in the good fat category.
One food gives us more of it than anything else.
And to show you, I'm at London's Billingsgate fish market.
There's some really amazing fish down here.
Fish is famously the best source of omega-3, and Professor Doug Tocher, a marine biologist from Stirling University, is going to show me which fish gives me the biggest helping.
Explain these test tubes for me then, Doug.
These test tubes show the amount of oil you get in a portion of salmon or sardines, compared to tuna and cod.
So that represents the salmon and that one is the cod.
That's correct.
What's really surprising is the salmon looks like it's almost got 20 times more oil in it than the cod.
Yes, that's correct.
There's a lot more oil in the salmon, but remember, that oil's good oil.
It contains a high concentration of omega-3 and delivers a high dose of that to us.
The cod and tuna are still very good for us, but they don't deliver the same high dose that you get with the oily fish.
So oily fish are the best source of omega-3.
This is like an omega-3 corridor.
So we've got Mackerel, this side, salmon, this side.
Just one portion per week gives us all we need.
So why do some fish have more oil in them than others? It's just because some fish store their fat in their livers, like cod, hence we get cod-liver oil that's rich in omega-3.
Oh, yeah! And other fish store their fat within the flesh, and they're the so-called oily fish.
So when we eat these fish, we get the biggest dose of omega-3.
But what if you don't like fish? Well, what's really exciting is that the food of the future could soon be packed with omega-3, thanks to some ground-breaking new science.
And, amazingly, the place we'll get all this extra healthy fat from is water.
We've got some live seaweed down here, look.
That's a pool there, isn't there? 'Dr Carol Llewellyn from Swansea University 'is an expert in marine algae or seaweed.
'We're all familiar with it on the beach, 'but Carol's more interested in algae so tiny, 'we can't even see them.
'They're in the seawater itself.
' And here it comes, right on cue, the sea! So, all this is full of algae that we actually can't see? Yes, they're microscopic living cells, and these actually do contain high levels of omega-3 oil.
Wow, OK.
Shall we collect some and have a look at some under the microscope? Yep.
This water looks crystal clear, but it contains tiny, invisible algae with a hidden bounty of omega-3.
Magnified hundreds of times, a whole secret world of tiny algae.
So there they are.
And they're all different shapes and sizes and colours.
We can see three or four different varieties, but actually, in the ocean, there are thousands of different microalgae.
They look really, really pretty.
Like pieces of jewellery.
They're stunning, actually.
Amazingly, minuscule algae cells can contain up to 50% oil, so they're a massive potential source of omega-3.
Trouble is it could take tonnes of seawater to end up with just a few spoonfuls of oil.
So this is the greenhouse.
Come on in! 'So Carol is trying to grow her own, on an industrial scale.
' This looks like some giant sunbed.
Well, I suppose it is, for the algae that are growing in it, because the algae actually need light to grow and multiply.
Inside these pipes, the algae are concentrated up to a million times more than in the seawater, and this makes it possible to get our hands on their precious cargo of omega-3.
We can then take the algae out and dry it, and I actually have a sample here of the dried biomass.
So that is dry microalgae? Absolutely.
You've got it in one.
Suddenly, we've got microalgae that we can see.
Yes, and you could actually eat this as it is and it's very rich in nutrients and in the omega oils.
Always up for a go.
It's really salty! It's just like taking a concentrated tablespoon of salt! We can go one step further and extract the oils from that to actually produce a pure algal omega oil.
So it's cutting out the middleman Or the middle fish! Yes, you could say that.
You can buy algal products in health food shops, currently, and I'm sure that, as years go by, it will become a more mainstream source of food.
So it's a future food? It's a food for the future, and it's also very sustainable.
But eating this stuff ourselves isn't the big idea.
What could really transform our food in the future is feeding it to animals.
On this farm in Shropshire, Professor Liam Sinclair has tried feeding microalgae to sheep.
And now he's about to start giving it to cattle.
The aim is to produce meat and milk that's rich in omega-3.
We're looking at feeding the microalgae to dairy cows and to beef animals and trying to see if we can get it into the milk and then, subsequently, into products such as cheese.
If this works, Liam predicts that we could get about 15% of our omega-3 from dairy products.
Our aim is that people can increase their intake of omega-3 without necessarily having to eat fish because a lot of people don't like fish and fish sales are decreasing and the overall objective is to improve people's health without them necessarily having to alter their diet.
So we may be looking at a future where we can get our omega-3 from a whole host of everyday foods, from beef and lamb, to milk and cheese.
Right now, we haven't quite cracked how to make it on a big enough scale to be commercially viable.
So in the meantime, it might be worthwhile learning to like fish.
After a whole week of going fat-free, our volunteers are back.
Welcome back, everyone and first of all, a huge well done.
What was it like? It has been a really difficult journey, really difficult to make food taste nice.
I found it really hard, mainly because a lack of energy.
I ate plenty, but I planned everything, I had to plan everything I had to eat.
Glad to hear some people planned, but I didn't, and that was really tough.
First morning, I had salad with fat-free yoghurt.
Strawberry flavoured.
LAUGHTER You put strawberry yoghurt on your salad? I wanted a bit of taste so the strawberry I didn't know what else to eat.
How was it? Horrible.
So you haven't discovered something, then? No, not at all.
How do you feel about stopping today? ALL: Yay! None of you were tempted to carry it on? ALL: No! That's all right.
Wouldn't recommend it, anyway.
Of course, this was a really extreme thing to ask you to do, to completely take fat out of your diet and it's not something, in general practice, we would advise people to do to try and lose weight, for example.
It's not a healthy way to do that.
So I'm glad none of you want to carry it on because we wouldn't recommend it.
In their seven days without fat, our volunteers felt hungry, bloated, constipated, and lacking energy.
To measure some of the effects the week has had, Professor Jane Ogden is running some tests.
Tell me the colour of the ink and not the word, OK? And go.
Blue, red, green, red, blue, blue, green, red One dramatic finding is how their levels of tiredness changed.
Pretty much everybody felt more fatigued and tired and everybody had much less energy.
Jane also tested to see if cutting out fat had created unconscious desires in our volunteers' brains.
Using an eye tracking device and pictures of different foods we can see what they were most drawn to before and after the week.
What we find at the beginning of the week is that really, they just look all over the place and you can see the results are mixed.
They are looking a bit at the salad, a bit at the cheesecake, they're looking a bit at the bread, but they are looking all over the place.
This is a typical response from the beginning of the week.
The green colour shows a low intensity of eye contact pretty evenly spread across the foods.
Now let's look at the same volunteers' responses at the end of the week.
After a week of no fat, the chocolate brownie gets much more eye contact, as does the burger and chips.
The fruit salad gets less eye contact after the fat-free week.
And look how this volunteer focuses on the vegetable plate.
Even on the vegetables, but not really on the vegetables, on the dip.
I think that one is fantastic.
They have bypassed the cucumbers and carrots and gone for a bull's-eye straight onto the dip.
So whose is that one then? That is Rashmi's.
I was thinking about the dip cos I just love avocado.
I was really craving.
That's why.
What's nice about the eye tracker, I think, is that even if you're not consciously aware that that's what you're drawn to your eyes are still going there and that's what this can pick up.
The zero fat challenge has altered the thoughts, behaviour and emotions of all our volunteers.
Larger scientific studies have shown that in the long-term, extreme fat reduction may affect our mood and can even increase anger and hostility.
For our volunteers, zero fat week is over.
So we've laid on a healthy spread that should satisfy their cravings.
This is nice.
They obviously look really pleased.
Yes, I think it just shows what a massive role fat plays in our everyday eating.
They've been so restricted with the amounts and types of foods that they can eat when trying to follow an eating plan free of fat.
Fat is one of our three main nutrients and if you suddenly take that out, you have to eat a lot more of the other nutrients, which can have symptoms in itself.
And also, fat gets a really bad rep, but it plays an important role in our health.
And as these guys have noted you get symptoms if you don't eat it.
There's so much choice These foods are good ways to eat the right kinds of fats.
Unsaturated olive oil, avocados, oily fish, nuts and seeds, together with a moderate amount of dairy, lean meat and plenty of veg, we won't go far wrong.
As a doctor, I know that fat belongs in our diet and in our bodies.
But it is really difficult to shake off that sense of fat somehow being the enemy.
But these guys have shown that fat really does play an important role in the food that we eat and that life without it is unpleasant and difficult.
The idea that fat is bad is wrong.
We've just got to make sure that we eat the right amounts and the right kinds.
Next time, the truth about Britain's top-selling over-the-counter medicines.
You don't often visualise what's happening to medicines once you put them in your body.
From painkillers to cough syrups, are these common cures all they're cracked up to be? This leg now feels like it is on fire.