- This post is about research published in April 2010. For analysis of November 2010’s paper in the British Journal of Cancer, read this post.
Fruit and vegetables have a small protective effect against cancer
Today’s headlines are loudly proclaiming that the message to eat five daily portions of fruit and vegetables isn’t all it’s cracked up to be. “Fruit and vegetables have little effect on cancer risk,” says the Guardian. “Five fruit and veg a day does not significantly reduce cancer risk,” says the Telegraph.
These claims are based on a new report from the largest ever study of diet and cancer. Here, we look at what the paper actually showed, how this fits in with the history of the five-a-day message and, most importantly, whether it means you should still try to eat plenty of fruit and veg.
What did the study show?
The latest paper comes from the EPIC study (the European Prospective Investigation into Cancer and Nutrition), the largest study ever on diet and cancer, part-funded by Cancer Research UK. EPIC looks at around half a million people from a variety of European countries. With its large size and the varied diet of its volunteers, it’s well-placed to look at potential links between the things we eat and our risk of cancer.
The study found that eating 200g of fruit and vegetables a day (2 and a half portions) was associated with a 3 per cent lower risk of cancer. Compared to people who ate less than 2.5 portions a day, those who got their five-a-day had 9 per cent lower risk of cancer. And the heaviest fruit-and-veg-eaters, who were eating more than 8 portions a day, had 11 per cent lower risk.
All of these results were adjusted for other things that can affect the risk of cancer, including smoking, alcohol, use of HRT, physical activity, social status, body weight, meat, fibre and more. These statistical adjustments are done so that, as far as possible, the statistics should reflect the effects of fruit and vegetables alone.
The study also found a statistically significant “dose-response effect”. This means that the more portions people ate, the lower their risk of cancer.
If the study’s results are to be believed, the authors calculate that if everyone ate two more portions a day on average, then 2.6 per cent of cancers in men could be avoided, as could 2.3 per cent of cancers in women. In the UK, this equates to around 7,200 cases of cancer every year.
Does this mean that experts were wrong?
Not quite. It actually fits very well with our current understanding of diet and cancer and how that understanding has changed over the last decade. Unfortunately, the headlines haven’t quite caught up with the science.
If you look back to the late 90s, fruit and vegetables were often touted as the big thing in cancer prevention. In 1997, the World Cancer Research Fund claimed that there was “convincing” evidence that fruit and vegetables reduce the risk of mouth, oesophageal, lung, stomach and bowel cancers.
In 2003, the World Health Organisation’s World Cancer Report said that the protective effect of fruit and vegetables against cancer was “the most consistent finding on diet as a determinant of cancer risk”. At that stage, around 80 per cent of the 250 or so existing studies found that eating more fruit and vegetables was associated with a significantly lower risk of cancer.
However, most of this evidence came from ‘case-control studies’. In these studies, cancer patients (cases) are compared to healthy people (controls) and asked to remember their choices and habits many years back to see if these affected their odds of developing their disease.
These studies all have basic problems. People might give inaccurate answers. There may be important differences between the cases and controls, especially in terms of other aspects of their health. And the studies might not adjust for other things that could cause cancer, such as whether the volunteers smoked or drank alcohol.
Since then, far larger ‘cohort studies’ have been published. These are generally a more convincing source of evidence. They follow a large group of healthy people, ask them questions about their lifestyles and wait to see which of them develop cancer or other diseases. In collecting information here and now, these studies are less vulnerable to the distorting effects of faulty memories. EPIC is one of these studies, and one of the largest ever done.
The results from cohort studies have been less charitable to the protective effects of fruit and vegetables. The long list of cancers that these foods supposedly protect against has shrunk. However, even cohort studies have found that people who eat the most fruit and vegetables have a lower risk of certain cancers, especially those of the digestive system – mouth, oesophageal and stomach cancers.
These changes are reflected in the latest assessments of the evidence. The WCRF’s second expert report, published a decade after the first, downgraded the evidence for mouth, oesophageal and lung cancers to “probable” and that for bowel cancer to “limited”. The report claimed that recent studies have made the overall evidence “less impressive” and “less compelling”.
So the results from the latest EPIC paper aren’t all that surprising. If fruit and vegetables only really reduce the risk of a handful of cancer types, then you wouldn’t expect to see much of an impact against cancer overall (remember that cancer is a collection of over 200 diseases).
Indeed, previous EPIC publications have reported that fruit and vegetables could reduce the risk of cancers of the mouth, larynx, oesophagus, bowel and lung, but they have no effect against breast, prostate or ovarian cancers, or lymphoma. And the similarly large NIH-AARP study found a link between eating lots of fruit and veg and a lower risk of head and neck cancers.
So should we still get our five-a-day?
Yes. Even if fruit and vegetables have a small protective effect against cancer, that’s still an important contribution. Remember that this study found a small benefit against cancer overall, but EPIC has previously documented more substantial benefits against specific types of cancer.
The problem comes when five-a-day is sold as the be-all-and-end-all of healthy eating. It’s not – it’s just part of a larger package of healthy lifestyle choices. Certainly, in terms of your diet, there are very few things that make a big impact on cancer risk on their own. It’s far more important to eat a healthy, balanced diet, where the impact of each individual food, while small, can add up.
This is another reason why superfood stories in the press are so misleading. They paint a picture of individual fruits and vegetables as the ultimate answer to the tricky issue of cancer prevention. However, as we’ve seen above, this evidence often hails from weak studies.
There are also other reasons to eat fruit and vegetables other than to protect yourself against cancer. For a start, they’re not harmful; there’s no real flipside to consider.
They could indirectly help to reduce the risk of cancer. They could help people to maintain a healthy body weight by taking the place of more energy-dense foods in our diet. They’re also a good source of fibre, and the EPIC study has shown that eating lots of fibre is associated with a lower risk of bowel cancer. The link between bodyweight and cancer is firmly established and based on a large body of consistent evidence.
Finally, they could help to reduce the risk of other diseases, such as heart disease. Indeed, the Spanish arm of the EPIC study reported that that people who ate the most fruit and vegetables were around a quarter less likely to die of chronic diseases at a given age, than people who ate very little.
-Ed
Reference: Boffetta, P., Couto, E., Wichmann, J., Ferrari, P., Trichopoulos, D., Bueno-de-Mesquita, H., van Duijnhoven, F., Buchner, F., Key, T., Boeing, H., Nothlings, U., Linseisen, J., Gonzalez, C., Overvad, K., Nielsen, M., Tjonneland, A., Olsen, A., Clavel-Chapelon, F., Boutron-Ruault, M., Morois, S., Lagiou, P., Naska, A., Benetou, V., Kaaks, R., Rohrmann, S., Panico, S., Sieri, S., Vineis, P., Palli, D., van Gils, C., Peeters, P., Lund, E., Brustad, M., Engeset, D., Huerta, J., Rodriguez, L., Sanchez, M., Dorronsoro, M., Barricarte, A., Hallmans, G., Johansson, I., Manjer, J., Sonestedt, E., Allen, N., Bingham, S., Khaw, K., Slimani, N., Jenab, M., Mouw, T., Norat, T., Riboli, E., & Trichopoulou, A. (2010). Fruit and Vegetable Intake and Overall Cancer Risk in the European Prospective Investigation Into Cancer and Nutrition (EPIC) JNCI Journal of the National Cancer Institute DOI: 10.1093/jnci/djq072
Comments
craig spencer April 14, 2010
There seems to be a lot of head in the sand type comments here. Cancer research have intelligently and in a considered manner explained why the study is defensible and fair. They also point out that the report dosn’t contracdict the fact that fruit & veg still help to significantly reduce certain types of cancer. Why are people so defensive over the foundings? or cancer researchs response. Firstly theres the freedom of speech point, if we agree with it we have to defnd it, especially when we dont agree with someones argument (not say ‘there should be a law against the media saying such things’) and especially not when the article and cancer research’s response are both quite considered and intelligently point. You just need a critical mind. The findings are helpful because it can move the focus on to other things like fibre, water, sunlight, toxins, genetics and so on.
Michelle Ferrarin April 11, 2010
Thanks for the email Cancer Research, i am glad that people are being properly informed of all the facts. Perhaps it is time to start promoting 8 A Day instead of 5 A Day if that is what the research is suggesting. It may be an unrealistic goal for the nation, but it may shock people into realising how few fruit and vegetables they do eat.
Andrew Harmsworth April 10, 2010
I was pleased to pick up this blog via Twitter – thank goodness – as all the media headlines (including BBC Radio News!) seemed to suggest that fruit and veg are a waste of time. Even a 1% reduction in cancer rates would be more than welcome. Keep up the good work, CRUK!
Lyle April 10, 2010
My apologies. My last posting was leading this discussion in the wrong direction, I was making some irrelevant and uncheckable speculations about the media. Let me get back on track. Cancer is a very complex issue. Its causes could be one of, or any combination of, a number of factors: genetic, environmental, cigarettes, alcohol, diet, amount of exercise, obesity. Cure (and prevention of recurrence) is just as complex; one of, or any combination of: chemotherapy, radiation treatment, love and support from friends and family, “attitude” (e.g. belief in your doctor, belief that your going to get better, religious or other belief, meditation, “finding a meaning in life” etc.), diet, exercise, work, fresh air… I therefore suggest that in such complex issues, the media should refrain from simplistic analysis (or maybe in this case zero analysis?). Additionally, it seems plain to me that 5-a-day is much better for our general health than 5-a-week or zero-a-week. I don’t think we need to survey half a million people to figure that out.
Linda April 10, 2010
I had bowel cancer about 15 yrs ago and was one of the lucky ones to have survived healthily till now. Frienda were surprised I got it as I’ve never smoked,I exercised regularly and ate a good well balanced, mainly veggie diet. I still eat the same good diet with more than 5-a-day, exercise regularly and live every day gratefully. I am 62, still working and loving every minute.
I read all these sensationalist headlines and try to read between the lines to get at the truth. Nothing is ever as cut and dried as the papers make out.
Paul April 9, 2010
Did they measure cancer incidence of vegans ?
What I know from my readings; plant based diet works only if it excludes animal protein
Lyle April 9, 2010
Like many of the people who commented above, I felt that the EPIC study was reported in a biased and incorrect way in the media. It occurred to me that it would be in the interest of the fast-food industry, and other food, cereal and snack companies to have it reported in such a way, but there’s obviously no way I can check if there is any such connection. Perhaps R.J. Hanlon’s adage is more likely here: “Never attribute to malice that which can be adequately explained by stupidity.”
Sue April 9, 2010
Probability is just a statistic not a fact. Like many others I know people who according to statistics should have died of cancer and are still alive and my husband who eat healthily, took regular exercise and never smoked died nearly 10 years ago of bowel cancer aged 46 – statistically he should be alive. We need to live for now and a healthy diet makes us healthier now so we can enjoy life more. It may / may not have an impact later in life. Statistics are about whole populations not individuals and should be reported by the media that way.
Thanks everyone for your comments. We’re glad that the post was useful and has helped to cut through some of the confusion caused by the coverage of this study.
Because EPIC is a large international study, with different centres taking the lead for different papers, we sometimes don’t hear about publications before they come out. When they do, we can only say so much in our media responses and our quotes are often cut anyway. This is why we chose to do a lengthier piece in the blog to provide some much-needed historical context to the debate.
We recognise that advice about diet and cancer can be confusing and that headlines seem to constantly swap their positions. Our stance on this topic has been very consistent for years. We have advocated a healthy, balanced diet rather than recommending any particular food or group of foods. When we have discussed five-a-day, it has been in the knowledge that it has some direct benefits against certain cancers and much broader indirect benefits in terms of keeping a healthy body weight and contributing to a generally healthy diet.
Alison April 9, 2010
This does not come as a surprise to me. Relying on one aspect of diet as a preventative for cancer is only partially helpful at best and potentially misleading. It does little to promote the holistic requirement for good health . By this I mean the reponsibility we all have to maintain balance and equlibrium in all aspects of our life: mind, body and spirit. By all means eat your 5 a day as part of a nutritious and balanced diet; exercise your body, have fun, laugh a lot, meditate and find your source of inner peace and definately Ignore narrow minded, negative & sensationalist headlines.
Erica Woolmington April 9, 2010
I will keep eating my five a day (and more). It can only do good. It seems cancers would show themselves more without the five a day. The media love to pick at reports and senationalise them. “Read between the lines” is what I say. Everything in moderation, and definitely no smoking
Kevan Gelling April 8, 2010
I think it’s a tad disingenuous to now complain “The problem comes when five-a-day is sold as the be-all-and-end-all of healthy eating”. CRUK has promoted 5-a-day for a long time. In 2007, Henry Scrowcroft in this very blog exclaimed “there is a large amount of evidence that five-a-day can help lower the risk of other cancers” and it’s hard to find any caveat in CRUK’s press release from Sept 2007 titled “UK failing to eat 5 a day” – http://info.cancerresearchuk.org/news/archive/pressrelease/2007-09-21-uk-failing-to-eat-5-a-day.
The 5-a-day message has been very successful – it’s on the lips every nannying health official and in the nutrition section of every Sunday supplement. It’s become part of the nation’s psyche – the incredulous comments above show how 5-a-day has become a dogmatic belief far removed from the original scientific evidence.
CRUK can argued that the original cautionary advice may have been hijacked by politicians and the media but I don’t remember CRUK ever protesting that 5-a-day was being oversold.
samuel timberlake April 8, 2010
i have been a vegan and vegetarian all i am 49 everyone who knows me or meet me for the first time thinks i am much younger, with the excepion of a fue common cold i have never fell ill: therefore eating fruit and veg not only keep you in good health but it keep your weight down and young looking.i thing alot of people like to scare mungering, and want us to eate more meat because its good for busines,because veg and fruit is less proffiting,in a frue years time they will say again that fruit and veg is good for health and not just canser but a way to combat obisity. a fue years ago they said the same thing about coffe and chocholate, now they said its good for us.
Tom Frank April 8, 2010
GLad you cleared that up, I did not get chance to see the details of the study but people will inevitably jump to the conclusion that eating fruit and veg is not helpful. This is typical of the press getting half a story!!!
Two things come out of this, I never thought that cancers other than of the digestive system would be affected, the relationship between dietary fibre and cancer of the colon has been well known for a long time.
The second thing that people do not realise is that cancer is not of itself a disease but the result of a disease process which itself may have many different causes. People keep on talking of “conquering cancer” as if it were one thing, and it is not.
Yours
Tom Frank
Martin Groak April 8, 2010
What studies have consistently shown is that people who follow a diet with a high content of fresh fruit and vegetables generally consume lower quantities of(and excrete higher quantities of) damaging fats and therefore have healthier guts and hearts and fewer obesity problems. The lower incidence of certain cancers is simply an additional bonus. No-one will live forever and shouldn’t expect to. It is the quality of the life we live that is at stake. There is no need to be ‘religious’ about food types: moderation and variety are the key.
Nancy April 8, 2010
I think that it is important to eat fruit and vegetables as part of a healthy diet and lifestyle (exercise, effective stress management etc). However I think that we do not truly know enough about the potential carcinogenic effects that pesticides and fetilisers may have in the human diet as an indirect outcome of consuming fruit and vegetables. It seems to me that the jury is still out on this issue. For example, the incidence of oesophageal cancer has increased massively in the last 30 years (whilst 5 year survival rates have remained consistently low at about 8%). I wonder whether we are only now begining to see what the longterm impact of pesticides and fertilisers may be. I think this issue should be addressed so that we can eat our fruit and vegetables with the confidence that we are not simultaneously also exposing ourselves to harmful chemicals as a by-product of attempts to eat healthily.
Jonathan Bagley April 8, 2010
I think, as mentioned by the authors in the final paragraph, the most important issue arising from this paper is what importance should be placed on analyses showing very small changes in risk, given the possibility of residual confounding and bias, exposure misclassification etc. This is why the authors are reluctant to highlight your figures for very high consumption of fruit and vegetables.
It would be helpful to the public, were you to translate these figures into reductions in absolute risks. Assuming the inverse association between f and v intake and cancer is causal, the authors give an estimate of around 2.5% of cancers avoided, or 7000 a year, were each person to eat an extra 2 portions. This roughly means that of the 600,000 people who die each year, 7000 fewer of them would die without having had cancer. Each person will have reduced his probability of suffering cancer by 0.016 or 1 in 63. It all depends on how much you dislike vegetables and whether you would much prefer to die before suffering cancer.
It is heartening that CRUK now recognises the superiority of cohort studies over case control studies. It was largely from meta analyses of case control studies displaying small relative risks that evidence for significant harm from passive smoking was concocted. The largest cohort study by Enstrom and Kabat (2003) was published in the BMJ and attracted comments more in keeping with the BBC’s Have Your Say message board, than a supposedly scientific journal. Suffice to say, the righteous weren’t happy and there is no danger of anything other than highly supportive of further measures against smoking being published in the BMJ in future.
I think that CRUK will be more successful in the long term if remains a respected scientific body rather than gives into temptation and turns into an ASH-like propaganda organisation.
So, what rating do I get? How about a bonus for actually reading the paper and not choosing to remain anonymous?
ojara April 8, 2010
I eat fruits and vegetables because they contain helpful fibres and Iodine. My belly is neatly trimmed because I eat fruits and vegs. What actually makes me sick are some of these unfounded claims by the media.
Malcolm Walker April 8, 2010
I thought the BBC 4 report on this particular headline was a bit lacking in balance and therefore dangerous, as it only seemed interested in rather knocking what has previously been thought to be axiomatic. (like eating veg. is good for you.)
It seemed to understate its value in all other respects (ie heart desease, digestive/bowel problems etc etc)- and what’s insignificant of 3% anyway? 7000 cases must be pretty expensive.
The other point worth mentioning is surely that by eating veg. like vegitarians, you will be contributing to the reduction of the demand for meat and therefore assisting in the lowering of the need for cattle and the production of methane.
John.Douglas.Clayton-Ferguson April 8, 2010
Personaly i think you should”nt listen to whats been said on the news becouse they are allways changeing there minds about servay”s and everone should eat as much fruit and vegtables for the vitamins minerals they provide
Greg April 8, 2010
I would have liked to have seen a more robust response from Cancer Research and other organisations arguing that fruit and veg should still be an important part of one’s diet alongside or within these articles in the newspapers. There seemed to be little balance. If Cancer Research were involved in the study in question, could their voice (with some of the details outlined on this page) be more publicised in the media, knowing that this information was going to be published? Nevertheless, I welcome this clarification; I now feel much better informed.
Kristina April 8, 2010
It’s always interesting reading the varying theories about cancer and diet etc over the last 15 years or so. My husband was slim, played sport, didn’t drink very much, didn’t smoke and had a healthy diet with daily fruit and veg, but 16 years ago, he developed bowel cancer at the age of 43 and died less than a year later. I know there are other influences, such as stress-related issues, which could have been affecting him at the time. There was at the time only one chemo drug which could be used in the UK, others were available in the USA, but not in the UK – it seems a shame that these drugs were not available at the time, he was prepared as I am sure many others are, to take the risks to have a chance of surviving. Within a few years other drugs were available.
Emma April 8, 2010
I don’t think there needs to be a law preventing the media from giving diet advice. We don’t need more laws, we need more common sense, which seems to be sadly diminishing. But I do think it was an irresponsible headline subject.
Eat more fruit and vegetables and do more exercise, like the article said, there is no flipside to that. Good old fashioned common sense, like brush your teeth and and don’t smoke.
David Lake April 8, 2010
What I think is that if you bombard any issue with enough research you can come up with any conclusion you like, which usually means that the prejudices of the researchers come to the fore. So called experts would be better employed finding a cure for cancer than causing inconclusive arguments over what we should and shouldn’t eat. You should never smoke, everything else is a matter for conjecture (in my opinion)
Keith Dancey June 1, 2010
My wife has not smoked or drunk alcohol for over thirty years, dislikes sweet food, loves eating lots of vegetables, keeps slim and active, yet five years ago she developed breast cancer, which she beat. Now she has just been diagnosed with incurable advanced kidney cancer.
People who think eating “five-a-day” will prevent cancer are just kidding themselves: the evidence is non-existent for MOST cancers, and – at best – slim for a few others.