WCRF reportLast month, the World Cancer Research Fund published a large report on diet and cancer that was greeted by a storm of finger-pointing, denial and outrage.

Henry’s already blogged about the report’s guidelines on obesity and red meat but I wanted to address some of the public backlash against the report.

A quick trawl of the BBC’s Have Your Say showed that most of the criticisms of the report (or it’s press coverage) fell into just a few groups. Let’s take a look at these.

“Leading a healthy lifestyle isn’t a guarantee”

As many commenters noted, you can be healthy and still get cancer. Healthy living won’t make you immune to cancer, but it will stack the odds of avoiding the disease in your favour.

In a similar way, there’s no sure-fire way of making sure you never become a victim of crime, but there are sensible measures you could take to make it less likely. You could walk down well-lit streets, in company, without flashy clothes or jewellery. The fact that you could still get mugged doesn’t mean that these precautions aren’t worth taking.

“I knew someone who was healthy but still got cancer”

Kylie Minogue was hardly obese, Lance Armstrong wasn’t exactly inactive and Linda McCartney didn’t eat any meat. All of them developed cancer. And many people know someone who developed the disease after living healthily, or someone else whose smoking, drinking or excessive sunbathing left them unaffected.

The fact that someone who leads a healthy lifestyle goes on to get cancer doesn’t make health messages invalid.

The point is this – health messages simply can’t be based on individual cases. A lifestyle choice could be the cause of one case of cancer, but be completely incidental in another. The only way to get a clear picture is to look at large groups of people and do some powerful statistics.

The health messages that are based on these studies then apply to groups of people. At this minute, many groups of scientists are looking at how genes modify the links between lifestyle choices and cancer, so recommendations may become more specific in the future.

“Scientists and health experts are always changing their mind”

Progress and change is a natural part of science and it’s a good thing. The alternative would be keeping a dogmatic stance even in the light of new evidence.

The problem is that media coverage of individual studies can give a biased view of what’s actually going on. Not all studies are good ones but the media frequently makes no distinction between small, poorly designed studies and large, rigorous ones. Every new piece of research is reported with equal weight.

Behind the scenes, science gives more credit to the stronger studies, and scientific opinion is only shifted by weight of numbers – by lots of studies that find the same thing. This is especially true if you’re trying to understand the causes of a disease as complex as cancer.

Imagine the evidence as a pair of scales. News stories might make you think that the scales are frenetically swinging from side to side, but they’re usually fairly stable and often heavily weighted in one direction. It’s actually very rare that a single study is so powerful that it tips the balance in the other direction. Usually, new evidence just makes the scale creak slightly one way or the other.

It’s ironic that so many people criticised the WCRF report as being another example of ‘scientists changing their mind’, when in fact, it was the opposite.

The report was the result of a group of experts getting together and having heated debates about the links between diet and cancer. It was about reviewing the current evidence in a scientific light, as only the world’s top experts on cancer prevention can do.

“It’s the preservatives, pesticides and pollutants in food that are the real problem”

In contrast to established risk factors like processed meat and alcohol, there’s actually no strong evidence that pesticides, artificial sweeteners or other man-made chemicals in food affect our risk of cancer.

Large studies in people have cleared artificial sweeteners like aspartame of any connection to cancer, even in people who eat and drink lots of sweetened foods.

There is some evidence that people exposed to very high levels of pesticides through their jobs may have higher risks of cancer, but the very tiny levels left on fruit and vegetables are extremely unlikely to affect your risk. And they certainly won’t overpower the benefits of the fruit and veg themselves.

These myths persist because of a belief that man-made chemicals are inherently bad for us, and that ‘natural’ chemicals are good. But this distinction is a false one.

The bottom line is that the things we eat and drink are going to affect our cancer risk much, much more than the very small traces of synthetic chemicals that they contain. Studies have consistently shown that alcohol causes cancer, while the evidence that pesticides in foods can do the same is weak and inconsistent.

That being said, Cancer Research UK will always consider any new evidence that says otherwise.

“We’ve heard it all before”

The principles of healthy living – balanced diet, healthy body weight, keeping active – are well known to most people. But surveys consistently show that many people are still largely unaware that these choices can affect their risk of cancer.

One of our own surveys (PDF) found that just a third of people knew that alcohol and obesity were linked to cancer, and just a quarter knew about the effects of inactivity (alcohol in particular, is often seen as a good thing as far as your health is concerned). In our survey, people were just as likely to name unproven links like power lines and stress as causes of cancer.

Clearly, there’s still a need to talk about proven ways of reducing the risk of cancer. This is especially relevant for people from the least well-off social groups, who are most likely to think that there’s nothing you can do to change your risk.

“We’re all going to die some day. I’d rather have fun now than to gain a few years of life.”

It’s often said that the chances of dying are always 100%. That’s obviously true, but a person’s lifestyle choices can have a massive impact on the length and the quality of their lives.

It’s worth remembering that most of the conditions caused by poor diets, high body weights and heavy drinking are chronic diseases, like heart disease, cancer, stroke and diabetes. This means that they can be long-lasting and recurring, and they can take away many years of healthy life.

The recent Foresight report found that obese people tend to lose an average of 13 years of life, compared to those with a normal body weight. And the British Doctors’ Study found that smokers lose about ten years of life compared to non-smokers (remember that this fact looks at the population as a whole, so a grandmother who lived to 100 on forty cigarettes a day doesn’t invalidate it).

With effects this large, there’s a lot of value in making positive changes as early as possible. It’s not our intention to tell people what to do or to stop them from having fun, but it is our responsibility to report important scientific findings.

Remember, making lifestyle changes may not protect your from ever getting cancer, but they might make the difference between getting it at age 50 or at age 70.

“You should leave people alone to get on with their lives – this is just more nanny-stateism”

Our health messages have never been intended as a rulebook for life. They are suggestions for how to reduce the risk of cancer and as an organisation dedicated to beating cancer, we have a moral duty to talk about them.

There’s no question that many cancers could be prevented. As we mentioned above, the only way to work out how to do this is to do large scientific studies.

Once the results of these studies are available, it falls on organisations to relay them to people. It would be grossly irresponsible of charities like Cancer Research UK and the WCRF to not talk about things that we know make people more likely to get cancer.

But the goal of these health messages is to allow people to make informed choices about their own risk.

Ultimately, everyone is free to make their own decisions.