Why Five a Day?

What's the evidence for 5 portions of fruit and vegetables per day? And do 5 apples add up to the same health benefit as mixed greens?
28 January 2014

Interview with 

Nita Forouhi, MRC Epidemiology Unit, Cambridge


Bowl of fruit


What's the evidence for 5 portions of fruit and vegetables per day? And do 5 apples add up to the same health benefit as mixed greens...?

Chris - Nita, keen on exercise?

Nita -   Sure, but keen on the other side of the energy balance equation too, which is the diet, which I think Dan just started talking about there.

Chris -   So, you're an epidemiologist.

Nita -   Yes.

Chris -   What is one of those when it's at home?

Nita -   In simplest terms, everyone knows what a doctor does.  You have a medical problem, you go along to a doctor, your GP.  An epidemiologist is somebody who deals with similar things, but on a population level, rather than on a one-to-one.  So, I would be interested in, why is it that hundreds of thousands of people get diabetes, or get heart disease, rather than focusing on the patient in front of me.

Chris -   What are you finding when you do these studies?

Nita -   It's really important to have this population perspective because the end of one as we would say which is anecdotal, which is things like, we have enough evidence that smoking is bad for us, but individuals may say, "But my grandfather smoke 80 cigarettes a day and he lived until he was 100, so what's wrong with that?"  so, the population perspective is really important for us to form credible research. And what we have been doing, the group the I lead, is specifically interested in understanding how diet and nutrition, and foods can influence the risk of developing diabetes. 

Now, for decades, the focus has been on, once you have diabetes, how can you control that well. 

It's common sort of folklore what diet should people eat to have better diabetes control. But, increasingly, what we now know is that to prevent the disease in the first place there are lots of things we could do.  So, with these big studies that we have setup - and when I say big, we mean studies that - for example - one that I will name, EPIC Norfolk - is 25,000 people around this area.  We have another study which is about half a million people.  So, we're talking big studies.  We asked people, people who don't yet have diabetes, what foods they're eating, what their regular habitual diets are like, and then we follow them up to see who develops diabetes and who doesn't. And we look at other disease end-points too.  From that, we can work out, what are the big things that can influence the risk of diabetes?

Chris -   So, you can find out what a balanced diet is and a balanced diet isn't perhaps an ice cream in both hands?

Nita -   So, you'll say, "okay, so you've got all these big studies.  What are your key findings?"  well, some of our very recent research has shown that for instance, eating high amounts of red and processed meat and also, drinking habitually one or more portions or cans if you like of these fizzy drinks or soft drinks can significantly increase your risk of diabetes over time.  We've also found things which can reduce risk of diabetes because we don't want to be only giving the messages of, "Well, if you eat this, this will up your risk of diabetes or of other diseases."  We also want to generate positive messages of what can you eat more of to reduce that risk.  I think, probably, no major prize's for guessing, we've found that fruit and vegetable intake is really important, but a particular nuance to that, recently that we wrote up a nice article about was that eating lots of variety of different fruits and vegetables is really important.  So, I think most of you know about the 5-a-day message which

is to eat 5 portions of fruits and vegetables a day for good health.  But we've recently worked out that, actually, if you are partial to say, apples, and you just eat 5 apples a day, that's actually not as good as going across a range of things, trying new types of fruits and vegetables, experimenting a bit.

Chris -   What do you think that 5 apples are not as good 1 apple, 1 tomato, a banana, and a cucumber and perhaps some lettuce then?

Nita -   Sure, really good question.  It's to do with the different types of content that you would get within the different fruits and vegetables.  Fruits and vegetables are full of thousands of what we call phytochemicals and they contain different proportions of vitamins, anti-oxidants, minerals, fibre content, the natural sugar content.  So, fruits and vegetables really vary in the amount of all these different hundreds and thousands of components.  So, by having a greater variety, you're taking the best of different types basically.

Ginny -   I've got a question that's come in on Twitter from Wayne Jemell, and he asks, "Which diet is better, a high protein - so I assume he means low carb diet - or a high carb, low protein diet?"

 Nita -   So, there's a lot out there about people favouring particular diets and there's a whole host of diets that are becoming very popular - high protein, low fat, and so on.  The distilled information from the research is, it has to be a balance of food components within the diet.  The foods have more to them than only protein and carbohydrates that present what we call macronutrients.  But there's a whole host of other things that we eat in foods that matter.  So, a healthy balanced diet - one, that will help you to maintain a healthy weight is the important things.  Different things work for different people.  Sustaining a particular diet is the hardest thing to do.  So, if you identify a diet that worked for you, that is the thing to hold on to.  There's quite a lot of research that it's the endpoint of maintaining good weight or losing weight if you're obese that matters.  Almost, whichever way you get to it, is not the critical thing.

Ginny -   Dan, I wonder if you want to come on in on that.  people are thin, they're trying to bulk up and perhaps put a muscle, think that they need lots and lots of protein.  Is that the case?

Dan -   Simple answer is no.  There's a couple of things on this that fascinate me with this.  There's a lovely saying that came from an American physiologist which is "fat burns in a carbohydrate flame".  So, to metabolise fat, you actually have to have carbohydrates.  So the idea of having a really low carbohydrate diet actually may well preclude you from burning fat and losing weight.  The second thing is, if we're talking about a balanced approach to life, we're talking about putting exercise in, then the currency that you need is carbohydrates.  So, if you're asking somebody to say, "Well, I actually want this balanced approach.  Go and exercise."  But actually, the approach is a low carb diet and then go and exercise.  You've all I'm sure experienced it where you get this idea of a sugar low.  It's the same equivalent.  It's like trying to make your car go on empty.  And then we come to the question of, bulking up on protein.  There's a lot of pros and cons to this, but the simple answer really is, that if you just ingest protein, you don't actually get it into the place you need it.  Again, carbohydrate is the currency that's needed to enable the protein to be actually taken into the cell.  So, if we go for a really low carb, high protein diet, the protein is not actually serving the role that you want for.

Chris -   So, watch what you eat on that restaurant menu.  What's your name?

Mark -   I'm Mark from Cambridge surprisingly, same as everybody else.  I was just wondering. You mentioned, lots of people have the processed food and processed meats in particular are quite a high risk factor.  I just wondered whether it's the food itself that's the main risk factor or something that gets done within the processing that's causing that to sort of keep coming up?

Nita -   The whole story is not known.  It's likely to be the things that are done to the processed meat itself such as preservatives added.  There are nitrites that are added and also, it could be the very high salt content of some of these preserved meats because salt is a great preservative.  So, it's a combination of both of those things that you mentioned.  In terms of the processed meat, the quality of it itself.  As I was saying earlier, there is the issue of saturated fat within it as well.  So, I think it's the saturated fat, plus, the things that you do to the meat to preserve it, together, that have the detrimental effect.

Victoria -   Hi.  I'm Victoria from Cambridge. It's a question relating to your suggestion that increasing your fruit and vegetables content will help prevent diabetes.  I'm just wondering why eating more fruits specifically will help prevent diabetes when you're trying to maintain a diet that's got a constant sugar level when fruit contains so much sucrose. I know it doesn't contain glucose, but in terms of how the body metabolises sucrose, why is that so much better for us than glucose from carbohydrates?

 Nita -   The main sugar in fruits is in fact fructose and fruits have a whole host of things within them, fructose being only one component.  So, what happens with eating fruit is that you get the combination of these benefits together, things like the fibre, the antioxidants, the phytochemicals, the carotenoids.  There's literally over a thousand components and beneficial chemical compounds within fruits.  That's why they're beneficial.  Now, in regard to your question about, or the worry about, the sugar content?  Taken together, the benefits of all these other factors outweigh any potential harm of the relatively small amounts of natural sugar that you will get from a portion of fruit.  However, if you were to have a glass of juice of the same fruit, you would actually then have a whole larger number of fruit to make that one glass of juice.  So there, proportionately, you would get a larger load of sugar coming into your body within acute response physiologically within the body.  But, eating fruits is actually a really great and healthy way to protect against diabetes, obesity and a whole host of other things because of those other components that go along with the sugar.

Chris -   What's your question?

Julian -   It's Julian.  I want to ask a question about diabetes.  There's a huge ticking time bomb we're told of about type 2 or late onset diabetes, but there were reports in the press to say that you can reverse type 2 diabetes by putting people on a very low - I think it was about 800-calorie a day diet for 6 to 8 weeks.  Do you have any further information on that?

Nita -   Yes, sure.  So, that is very promising and there are small scale studies of those research group that have come up with that idea where they have shown that indeed, that is the case if you put people on very drastically low calorie diets.  In fact, they were even lower than 800 calories, down to 600, even 500 calories, can lead to what we call a remission of diabetes if people have it.  And there are claims that it may even cause reversal of diabetes.  There are some big studies by those groups now planned, so that those experiments if you like can be done on larger numbers.  And also, to see the feasibility of whether people can sustain those diets for those 6, 8, 10-week periods of times, and how much input will be needed from, say, NHS staff to maintain people on those diets versus how much can be done independently.  So, a whole host of things to be worked out about feasibility and scope, but really promising.  And if that is the case, then even if it was remission rather than reversal, it is important to follow through on that. 

Chris -   One person said to me that these low-calorie diets, these extreme low-calorie diets, regardless of whether or not they add years onto your life, they sure is hell make it feel like you're living forever because it's so boring.  It's so hard to do.

Nita -   It makes you work hard!

Chris -   Ladies and gentlemen, Nita Forouhi.  Please show your appreciation.

Chris -   You're listening on the Naked Scientists with me, Chris Smith, Dave Ansell, Ginny Smith, and our esteemed panel of guests this evening, Dan Gordon, Nita Forouhi, and David Ogilvie.  We're talking about lifestyle and lifestyle choices, and how the world we live in can affect your health.  Nita, we've actually got a little experiment for you to take part in.

Nita -   Sounds fun.

Ginny -   So, we've been hearing a lot about how good for you, fruits and vegetables are and of course, one of the reasons they're good for you is because they contain vitamin C, but we were wondering whether, how you cooked your vegetables affected how much vitamin C was in them.  So, we've come up with a little experiment to find out.

Dave -   So, the first thing we've done is we've got three sets of carrots.  We took a set of carrots.  We put it into a blender.

Ginny -   So, we cut up some raw carrot, we mixed it with a bit of water and we popped it into a blender, and then we have to filter out all the sort of big blocky bits of carrot that hadn't blended up properly.  So, we put it through a coffee filter, just a normal one, and we came out with some rather delicious looking carrot juice.  Then we did the same thing for the same amount carrot that we had boiled - and we boiled it quite efficiently.

Dave -   To the point that where we actually boiled all the water away because we weren't paying attention.

Ginny -   So, this is kind of school dinners, carrot boiled until it barely resembles carrot. We also did some in the microwave.  So, we thought we would see how much vitamin C is contained in each of these types of carrot juice.  Nita, could you come and give us a hand for a second?

Nita -   Yes.  So, what am I doing?

Dave -   Now, we've got some carrot juice.  We're going to use a reaction between starch and iodine for this and...

Nita -   Takes me back GCSE Science.

Dave -   Very much so.  So first of all, we're going to add about 10 ml of...

Nita -   So, this is the raw, not boiled, not microwave carrot here.

Ginny -   Yes.  So, we're going to add some of these carrot juice to a cup that's already got a starch solution in it.  So, we just dissolved some corn flower in water.

Nita -   We're just pipetting this in?

Ginny -   Okay, so we've got some starch solution and some carrot juice in that cup and we also made up the same solutions with our boiled carrot juice and our microwave carrot juice.  Three orange

cups of carrot juice.  They don't look too appealing.  They're sort of slightly watery orange colour like maybe a very fake-looking orange squash.  Now Dave, what are we going to do to see how much vitamin C is in here?

Dave -   What we've got here is iodine solution and iodine can exist in two types - there's iodide and iodine and it's only the iodine which will react with starch and that gives you a really dark colour.

Ginny -   You might remember that from school, the sort of blue black colour you get if you drip some iodine on a potato or things like that.  Most people have seen that.  So, that's what we're looking for and, if we see that colour, that means that it's reacted and what does that tell us?

Dave -   The vitamin C will react with the iodine and keep it in the iodide state so it doesn't react.  So, the more vitamin C there is there, more iodine we can add before it will react.

Ginny -   Okay, so we're looking for different shades of blue.  The darker the blue, the less vitamin C is in our juice.  The lighter blue will mean there's more vitamin C in there.  So, you can put the same amount of iodine in each of our cups and see how much there is.

Dave -   About 15 drops.

Nita -   So, this is a fair test I hope which is 15 drops at each, and I'll be going to count this down?  1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 - okay, that was 15.

Ginny -   Okay, so I can see there's a really bright blue colour at the top here

and we're going to swirl it a bit and see what happens.  Okay, so it's staying quite dark isn't it?  Which one was that?

Nita and Dave -   That's the raw one.

Ginny -   Okay, well actually hang on.  It's starting to get a bit paler now.

Nita -   1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15.  There we go.

Ginny -   Okay, let's give that one a swirl.  Again, we've got a bright dark blue to start with and we're swirling it and same in the other one.

Nita -   So, that's the boiled one.  And now, the microwave one, there we go.

Dave -  The best... (laughter)

Ginny -   So, when we did this in my kitchen earlier, we got a slightly different result.  It's exactly opposite to what happened earlier.  Now, that's interesting.  So, when we did this

earlier, we found that the raw one was a much lighter colour.  It seem to have more vitamin C in it; then the microwaved one was in the middle, and the boiled one was the darkest.  We appear to have the opposite.

Dave -   I think we've actually discovered something new by doing this experiment which is, if you leave raw carrot juice sit and lying around for a long time, the vitamin C will actually get destroyed, probably by enzymes and things floating around inside the carrot juice.  But if you cook it, it will preserve it and it will last a lot longer.  But if you do it fresh, you will find there's a lot more vitamin C in raw carrot than cooked carrot and a microwave carrot is somewhere in between.

Ginny -   We did notice when we took the raw juice out, if you hold up one of the other ones, you can see that the cooked ones are beautiful bright vibrant orange whereas the raw ones gone kind of darker and duller, and it started off as similar colour to that ones. 

So, that shows us that in a couple of hours between making this in my kitchen earlier and bringing it to the show, something has happened to that raw one that's obviously got rid of some of the vitamin C.  Is that what you would expect to happen?

Nita -   Actually, no I wouldn't.  I would expect the goodness to be there.  The vitamin C should be there and it should be beneficial for you.

Ginny -   Fair enough.  There we go.  That's science. (clap)

Chris -   Anymore questions for Nita?

Mark -   Hi.  I'm Mark from Cambridge.  I was just wondering, to what extent do the positive and the negative risk factors cancel out?  I really like sausages, so is there an amount of fruit that I can eat to compensate for me eating the sausage or will the negative factor of the sauces never be compensated?

Nita -   Nice try.  It's all about the balance and it's not about, if I have a little bit of this, is that still bad for me and can the harm never be compensated for by the good things?  No, it's not like that.  It's about portion control.  It's about the balance of things.  If you are partial to some things, if you have it in moderation, or small amounts on the odd occasion, rather than a daily thing, then I think it kind of balances out.  Much of our research when we've analysed the data on these large populations does show that.  So, we are not kind of "party poopers" doing this research saying, "You mustn't eat this ever in your life."  The point is, certain things, if eaten regularly habitually, day in and day out in large quantities have the detrimental effect.  Having small amounts of something is okay, but yes, do eat the beneficial things on a habitual regular-and-often basis.

Chris -   Nita, thank you very much!


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