No one wants cancer. I think it’s safe to say that most, rational human beings will willingly commit to engaging in activities or behaviours that they know will dramatically reduce their risk of being diagnosed with a disease that is likely to kill you. Also, if you are a person who has ever spoken to another person you are most probably personally aware of at least five individuals who have suffered with cancer. Maybe some of those people died. The combination of our close proximity to cancer and our innate fear of our own mortality has led to a societal obsession with the disease and strategies to avoid a fate that inevitably lies ahead for a third of us.  Never is this obsession more obvious than within the sphere of diet.

Despite 450 Britons losing their lives to this insidious disease everyday – many of whom are perfectly healthy and enjoy a regular fill of fruits and vegetables – both media reports and dinner-table chat continue to push the theory that such fatalities are unnecessary. If only we all ate correctly, cancer cells would fail to flourish and the body would be armed with an almighty armour, batting cancer germs away as if they were nuisance midges. Depending on who you speak to, the proposed mechanisms vary. According to my waxist, hormones in cow’s milk interact with oestrogen in women to encourage the growth of cancer cells. A so-called ‘doctor to the stars’ touts the power of anti-oxidants in fruits and veg – enough of these, she says, and the body is equipped to kill the cancer, no problem. I even heard a blogger (who else) announce recently with passionate conviction; ‘where broccoli lives, cancer can’t’. Whilst I’d love to starve these arguments of oxygen, denouncing them all as nothing more than total idiocy, doing so would be a lazy disservice to the army of dedicated scientists who have spent their academic lives researching this area.

It is widely accepted within the scientific and dietetic community that there is a relationship between the amount of processed red meat (i.e bacon, ham, sausages)  and colorectal cancer (bowel and colon cancers). It is thought that the mechanism relates to the processing of the meat and certain chemicals that are released during the cooking or preserving stages, although scientists are still working to confirm the specific substances involved. The culprit, it is assumed, is a chemical called  N-nitroso – found in both blood and generated in the gut by some preservatives – which can damage the cells in the bowel, according to Cancer Research UK.  Despite what the Whole Foods converts will have you believe, there is absolutely no evidence to suggest that the cancer link is related to the quality of the meat, or whether you bought it from Aldi or your local, artisan butcher. Oh, and burgers, mince and all processed white meat aren’t included either – so eat as many chicken nuggets as you damn well want.

BUT there are a few things to bare in mind in order to understand the true risk. Firstly, the figures relate to the effect on a person’s relative risk of developing the disease. This means the risk in relation to what their baseline risk is already of developing colorectal cancer which, in the UK, is 61 out of 1000 people – so about six per cent.  Allow Cancer Research to explain the next mathematical part far more eloquently than I ever could…

“Out of every 1000 people in the UK, about 61 will develop bowel cancer at some point in their lives. Those who eat the lowest amount of processed meat are likely to have a lower lifetime risk than the rest of the population (about 56 cases per 1000 low meat-eaters).  If this is correct, the WCRF’s analysis suggests that, among 1000 people who eat the most processed meat, you’d expect 66 to develop bowel cancer at some point in their lives – 10 more than the group who eat the least processed meat.”

Cancer Research UK

As always, dietary studies involving diet questionnaires, must always be approached with some caution as it is almost impossible to pinpoint one food in particular as being the sole cause of anything. Processed, red meat eaters also tend to be male, older, larger, less physically active and more stressed – all factors that are also known to increase the risk of cancer. What’s more, the risk only applies for those who eat more than 70 grams of processed, red meat daily and according to the latest National Diet and Nutrition Survey, most of us are averaging that amount anyway – with women consuming an average of around 56 grams daily – more than 10 grams below the limit.  Basically, for most people it’s a case of eating one less sausage a day and maybe making sure at least one day out of the week is processed, red meat free. I’m gonna hazard a guess that most of you lot aren’t devoted to a full english every single day…

Non-processed red meat (fresh pork, beef and lamb) has also been highlighted by the same study as being linked to an increased risk of colorectal cancers. However the study doesn’t differentiate between red and processed meat so again, consider the information with caution. The NHS advise covering all bases by reducing both processed and red meat down to 70 grams per day which, again, is probably something you are already doing (50g is one pork sausage).

Cancer Research UK helpfully put this risk in perspective by comparing it to tobacco. It is estimated that 86 per cent of the lung cancers in the UK are caused by smoking, whereas just 21 per cent of bowel cancers are thought to be the result of a diet high in processed, red meat. So although we are aware there is a risk, it’s nowhere near as dangerous as smoking. The World Health Organisation’s International Agency for Research on Cancer classify processed, red meat as a Group One Carcinogen meaning that it is accepted that it causes cancer. This sounds scary, but it’s worth baring in mind that alcohol is also listed in this category – and I bet you posh totty wellness bloggers wouldn’t say no to a glass of bubbly on a Friday night for fear it might go all cancer-y.

Now that I’ve tackled the food-cancer links that are steeped in evidence, it’s time to look at the ones that are not.  I called on three cancer experts to help me figure out if there was anything I’d missed on my cancer travels (lol) or if I was right to assume that 85 per cent of the diet/cancer articles I read are nothing more than unscientific, evangelical BS. Specifically, I sought the help of physicist and cancer researcher, David Robert Grimes; health information manager at Cancer Research UK, Emma Shields and Paul Pharoah, Professor of Cancer Epidemiology at the University of Cambridge.

1. ARE THERE ANY FOODS THAT CAUSE CANCER?

Emma Shields:  “It’s a really interesting time with diet and culture, but actually the more it has been studied, the more we see that it is very unlikely that individual nutrients and diets that can have an influence on your risk.  There is strong evidence that processed meat and red meat can increase risk of bowel cancer, and that fibre and whole-grains can reduce the risk of bowel cancer.  But when we’re looking at individual foods and risk there is not strong evidence.”

Paul Pharoah:  “Identifying specific components of diet is tough. It’s not as simple as saying, ‘if you eat less bacon everyday you won’t get cancer. There’s lots of chemicals in the stuff we eat and it’s very difficult to separate one ingredient from another and look at how it acts in the body. We know that less animal meat probaby a good thing but even there, the evidence is not that strong.”

David Grimes: “We might see an association of cancer with a particular diet, but even then there are many other variables that confound the picture. We know for example, that a diet high in processed meat is associated with a small increase in the risk of bowel cancer, but even here the dose maketh the poison, and it’s not precisely clear why this would be.”

2. CAN I REDUCE MY RISK OF CANCER BY CHANGING MY DIET?

David Grimes: “There is a very simple way to reduce one’s cancer risk by diet – eat a varied, balanced diet, and try to maintain a healthy weight. Obesity is associated with some cancers, and by keeping to a safe weight one can reduce their risk. Again, it’s not a case of demonising one food type or subgroup – just ensuring we eat a healthy, varied diet.”

Emma Shields: “Overall, around 4 in 10 are preventable  [at the population level] largely through lifestyle changes. That figure is a sum of all those risk factors – such as smoking, drinking and obesity.  Obesity is preventable through a healthy, balanced diet, so one higher in fruits, veg, pulses and lower in high energy foods.  We know that obesity is the second biggest risk factor after smoking but we don’t understand exactly why. The most likely explanation is that extra body fat can cause high levels of hormone and inflammation which equals greater cell division, but there are other methods that are being looked into also. Abdominal fat seems to be potentially more harmful [than fat in other areas] but most evidence is based on BMI, not body fat.”

Paul Pharoah: “We know that unhealthy diets can be risky in terms of cancer risk because being overweight or obese is associated with an increased risk, but even with that association, the mechanism at work isn’t entirely clear. Losing weight reduces cancer risk by a noticeable amount but identifying specific components of the diet is tough. It’s about limiting the calories whatever the source to make sure you are not overweight or obese which is, generally speaking, just eating a healthy balanced diet. Under natural circumstances that would be easy – animals will naturally eat a balanced diet – but when a single food source is so easily available as high calorie foods are today, people eat a little too much.”

 

3. WHAT ABOUT HORMONES FROM COWS MILK? DOES THAT CAUSE BREAST CANCER?

Paul Pharoah: “People dream up assumptions of possible mechanisms that they think explains something but it’s based on absolutely nothing. There is no good evidence linking dairy with breast or ovarian cancer. There are groups of people who like to rally against industry and say all these illnesses are caused by big pharma e.t.c. but they are just using pseudoscience to justify their advance or their stance. Lots of hormones – from animal wastage – in the environment is probably not a good thing but hanging health issues onto that isn’t reflective of the truth or the research.”

Emma Shields: “There’s actually strong evidence that dairy products can reduce the risk of bowel cancer. We think this is possibly to do with calcium content. The hormonal link has not been proven and there is no good evidence that dairy products influence the risk of breast cancer.”

David Grimes: “With regards to cancer, there is to my knowledge no reputable links between food hormones and human cancers. In diary for example, the hormone bovine somatotrophin (BST) is used in some countries to accelerate milk and meat production. However, farmers in the EU are banned from using his hormone, and import of meat from countries using it are also banned. But this ban is based on animal welfare grounds, not issues of human health. BST has been reviewed by independent health bodies including the European Union Scientific Committee, who have found zero evidence linking the hormone to cancer risk. I think the issue here is one of misunderstanding – the idea that if a human cancer has a hormone relationship, then hormones are ‘bad’. Of course, hormones in animals are entirely different to our own, and don’t work that way – but it’s easy to see when the misconceptions arise.”

4. SO CAN WE TRUST STUDIES OR NOT?!

Paul Pharoah: “There’s a lot of rubbish science that gets published!  It’s all epidemiological research when it comes to diet which is hard to study without biases.  It’s very difficult to show that there is no association with other factors too.”

David Grimes: “Diet is complex to study, and often times we have correlations but no clear arrow of causality. Headlines simplify study findings, and in the process delete most of the crucial caveats. For example, the effect might be so negligle as to not pose any concrete risk, or a spurious findings which are very common. A single study itself rarely provides a smoking gun in any case – to establish clear links requires an overhwhelming weight of evidence, and sometimes an apparent effect disappears once other variables are accounted for. Rushed headlines instilling fear may shape public opinion, but they certainly do not make us healthier. The crux of the problem is cancer epidemilogy is hard, and convoluted. An association doesn’t mean a cause, and even when it exists the net effect might be marginal.”

Emma Shields:  “Diet is the hardest factor to study. There are lots of different factors that come with it and trying to measure diet alone is incredibly difficult. There are always limitations. Studies will be adjusted for co-existing factors but there is a chance that there might be some residual bias.  Unhealthy behaviours do cluster together. It’s a package of behaviour and of course there are socioeconomic gradients.

If you look at the studies with acrylamide – the recent headline that burnt toast causes cancer – most of the research comes from animal studies showing acrylamide (a chemical emitted when some foods are burnt) may potentially damage DNA, but when we look at human studies we can’t see any evidence of this strong link.”

 

5. WHY IS EVERYONE SO OBSESSED WITH CANCER?!

David Grimes: “Sadly, there are myriad misconceptions about cancer, and dubious misinformation propagates online at blinding speeds. If you were to google it, you’d find legions of people claiming they can cure cancer with everything from apricot speeds to cannabis oil to homeopathy. Others state there’s a secret cure suppressed by the nebulous big pharma, and others still assert all kinds of ostensible cancer causes simply not supported by any scientific evidence, from WiFi to dairy. This is a problem I write about constantly, and misinformation has an extremely detrimental impact on patients, making it nigh on impossible to separate signal from noise.

I think part of the reason for the abundance of nonsense is the ubquity of cancer, and the fear around it. Even though survival and treatment has improved year on year, we are still loathe to talk openly about cancer. In that void, charlatans and fools are only too happy to push their own dubious narratives. It’s incredibly hard to combat, but the crucial point is that patients and their families maintain a very healthy scepticism of cancer claims online, and talk with the physicians about fears they might have. There are also several highly reputable outfits who do excellent information guides, such as Cancer Research UK. But certainly, one has to be extremely wary of simple claims made about a complex family of illnesses.”

 

For more information visit Cancer Research UK’s diet hub.