Scientists across Europe studied the effect diet could have on someone's risk of cancer.

In this instalment, we look at how our researchers helped answer the question “can diet affect someone’s risk of cancer?”.

“Europe seeks a winning diet” hit the front cover of New Scientist in November 1991, announcing the start of an ambitious diet study.

Diet was a hot topic in the early 90s. And many thought what we eat could have a big impact on our risk of cancer.

The focus was fruits and vegetables, with some studies suggesting that people who had cancer said they ate less fruit and veg than those who didn’t. Theories about vitamins and antioxidants helping to prevent cancer were rife.

Enter the European Prospective Investigation into Cancer and Nutrition (EPIC) study.

The evidence on diet and cancer was “nowhere near good enough”, says Professor Tim Key of the University of Oxford, one of EPIC’s lead investigators. This led Key and his colleagues to design EPIC so that the data was solid. And In 1991, they set out to answer the big question: can diet affect someone’s risk of cancer?

Using money from Cancer Research UK and other funders such as the European Union, researchers in Oxford and Norfolk began adding to the EPIC database, linking their results with those collected at other research centres across Europe.

Almost 30 years later, the results from EPIC have shaped our understanding of diet and cancer. And surprisingly, they’ve taught us more about what not to eat to help reduce our risk of cancer.

Hunting for an anti-cancer diet

Diet is a tricky thing to study. For one, it’s hard to properly measure what and how much we eat. And because what we eat is so varied and influenced by many other things, it’s hard to pinpoint if there’s one thing in our diet that could increase or decrease the risk of cancer.

Before EPIC, the main way scientists studied diet and cancer was by asking people with cancer what they’d eaten over the years. They also compared cancer rates between countries, assuming any differences could be chalked up to diet.

These studies can offer hints, but they have serious limitations. It’s hard enough to remember what you had for lunch yesterday, let alone what you ate over many years. And people who have been diagnosed with cancer may recall things differently to those who haven’t.

EPIC took a different approach. First, scientists recruited lots of healthy people and asked them upfront about their diet, lifestyle, and levels of physical activity, as well as taking blood samples. They then followed the people on the study for at least 15 years to monitor how their diet, lifestyle and health changed over time.

This gave the team the solid dataset they needed to work from. It meant they could now reliably compare the diets of people who had gone on to develop cancer to those who hadn’t, while also accounting for other factors like smoking.

“EPIC was cutting edge,” says Key

To get meaningful results, the study had to be huge. It involved more than half a million people who enrolled at 23 research centres across 10 countries in Europe.

No easy feat

Running a study this big isn’t easy. And the main challenge the researchers faced in 1993 was technology.

When the study began, all the participants filled in their study questionnaires by hand, giving the researchers the job of typing them up individually. The Oxford team alone had 65,000 questionnaires over 3 years.

Thankfully, improvements in technology did ease the pressure. Eventually, the team moved away from manual typing, opting for scanners instead. And the survey finally went online in 2010.

Coordinating the across 23 research centres wasn’t easy either. Thankfully, the World Health Organization’s (WHO) International Agency for the Research on Cancer (IARC) took the lead.

“We were very lucky to have funding and support from IARC. The link with WHO has been absolutely critical for our success,” says Key.

Data from the half a million participants, including blood samples, is held centrally at IARC’s headquarters in Lyon in one huge database and biobank.

What did EPIC find?

Scientists have published over 500 papers using EPIC data so far. And in some ways, the findings were surprising.

“When we started there was a lot of excitement around antioxidants and the thinking that more of these will actively prevent cancer. But we haven’t uncovered clear evidence showing that. It seems that with diet, you need enough of something, but eating a lot more doesn’t help,” says Key.

So if eating more ‘superfoods’ isn’t the answer, what is? Cutting back on processed meat and alcohol, according to EPIC.

Scientists found that eating lots of processed, and probably red meat, increases the risk of bowel cancer. These results formed a key part of IARC’s 2015 decision to classify processed meat as a definite cause of cancer in people, which we blogged about.

And it’s not just processed meat we should be cutting back on. Thanks to EPIC and other studies, we now know obesity is the biggest cause of cancer after smoking.

“Obesity and alcohol probably weren’t on top of the list when we first started, but results from EPIC, and other studies, have shown that beyond any doubt, both obesity and alcohol increase the risk of a number of different types of cancer,” says Key.

Scientists had originally thought that eating fatty foods could be the source of the problem, but the data from EPIC doesn’t support a direct link between dietary fat and cancer.

“What seems to be most wrong with the diet is eating too much overall. Too much fat on the body, no matter how it gets there, is what causes the problem,” says Key.

Of course, there’s an exception to every rule, and in this case, that’s fibre. EPIC found that eating more foods high in fibre (like wholegrains) reduces the risk of bowel cancer.

Leaving behind one EPIC legacy

EPIC was ground-breaking in many ways, but the collaboration between scientists across Europe was especially powerful. Today’s scientists are encouraged to work in this way, says Key. But the EPIC team were already doing this across Europe almost 30 years ago and have continued to do so to this day.

Thanks to EPIC, we now have much better evidence to respond when people ask: ‘What should I eat to reduce my risk of cancer?’. And it has opened up a more important message around what we should all probably eat less of.

This has helped to shape dietary recommendations, whether they come from the government, CRUK, or other health charities.

Not smoking is still the best thing you can do to reduce the risk of cancer. But it’s not the only thing. Keeping a healthy weight, eating more high fibre foods and less processed meat, as well as drinking less alcohol, are the solid choices we can all make to stack the odds against cancer thanks to the scientists behind EPIC.

Emma Shields is a health information manager at Cancer Research UK