Wholegrains and bowel cancer – what you need to know

Eating plenty of wholegrains cuts your risk of bowel cancer, according to a new report.

And it seems we can reap the benefits without making wild changes to our diets (unless your diet is mainly hot dogs and fry-ups).

The news comes from a report produced by the World Cancer Research Fund (WCRF) and the American Institute for Cancer Research (AICR), outlining the latest evidence on how we can reduce our risk of bowel cancer.

It focusses on the effects of diet, weight, physical activity and alcohol on bowel cancer risk. And with bowel cancer being the fourth most common cancer in the UK, finding ways to reduce our risk of the disease are important.

The WCRF studies all the evidence on a potential cause of cancer and decides whether that evidence is strong enough to support recommendations on ways we can reduce our risk.

For bowel cancer, we already recommend that people include plenty of wholegrain options in their diet. So the new report is welcome.

But what is a wholegrain? We take a look at what they are and how you can get more into your diet.

What’s new in the report?

The proven things you can do to reduce the risk of bowel cancer have remained constant over the years, and this report reinforces that.

What was true yesterday is even more true today.

Copy this link and share our graphic

The most interesting finding from the new report is that for the first time, the WCRF team looked at the effect of wholegrains on their own (a food high in fibre and other nutrients).

Previously, WRCF has only looked at the combined effects of foods high in fibre, and found that eating more of these can reduce the risk of bowel cancer. But other research looking at different types of high fibre foods has found that the strongest evidence for reducing bowel cancer risk comes from wholegrains.

And the conclusion of the latest report is that there is now strong evidence that both wholegrains specifically and a high fibre diet in general reduce the risk of bowel cancer.

What’s a wholegrain?

A grain is the seed of a plant. Grains are made up of three parts: the bran, germ and endosperm. During the milling process, the bran and germ are lost, leaving whiter refined grains, such as white flour. This part of the grain is mainly an energy store, so refined grains give you carbohydrates and some protein but not much else.

A wholegrain still has its bran and germ, such as in wholemeal flour. Most of the nutrients and fibre are found in these bits, which means that wholegrains are naturally more nutritious than refined grains. And this is the likely reason why wholegrains are linked with a reduced risk of bowel cancer.

Copy this link and share our graphic

How do wholegrains cut bowel cancer risk?

This is most likely down to the fibre they contain.

Fibre increases the size of your poo, dilutes it, and helps it move through your system quicker. This reduces the amount of time harmful chemicals stay in contact with the bowel, potentially reducing the damage caused to cells.

Fibre may also help gut bacteria produce helpful chemicals that change the conditions in the bowel.

This is why foods high in fibre have been linked with reducing the risk of bowel cancer for many years now.

But other things in wholegrains, such as phenolic acids, could also be playing a role, and may partly explain why wholegrains seem to show a strong link on their own.

Eating more high-fibre wholegrains and fewer refined grains can help you keep a healthy weight by feeling fuller for longer. This not only cuts the risk of bowel cancer, but 12 other cancers too.

How much wholegrain should we be eating?

The UK’s dietary guidelines recommend that we base our meals on starchy foods, and where possible choose wholegrain versions. But there aren’t any specifics on how much we should eat.

The WCRF report found, based on all the studies published on wholegrains and bowel cancer to date, that for every 90g of wholegrains eaten daily, there was a 17% reduction in bowel cancer risk. This is what’s known as a relative risk (more on that here), which tells us how much more, or in this case less, likely the disease is to occur in one group (people eating 90g of wholegrains), compared to another (people who didn’t eat wholegrains). And because this is for every 90g eaten it underlines that the benefits increase the more wholegrains you eat.

This isn’t a guarantee though, because relative risk can’t tell us about the overall likelihood of bowel cancer being diagnosed in any one person. But with more than 41,000 cases of bowel cancer diagnosed in the UK each year, a 17% reduction in risk could make a sizeable dent.

For example, we already know that eating more foods containing fibre, of which some will be wholegrains, could lead to 5,100 fewer cases of bowel cancer each year in the UK.

So 90g isn’t a magic number, and it doesn’t mean you need to start weighing your food. The key thing here is that by switching to wholegrain versions of your everyday starchy foods you can easily meet this amount and more. And every bit counts.

Copy this link and share our graphic

So whether it’s switching to wholemeal breads, opting for a wholegrain cereal at breakfast (such as porridge oats, shredded wheat, or Weetabix (or your supermarket’s own brand), having plain popcorn instead of crisps or choosing brown rice and whole wheat pasta, all these swaps can make a big difference. If you don’t eat many wholegrains, try switching for just one meal a day.

Wholegrains vs. hot dogs

It’s not just wholegrains we should be thinking about when it comes to bowel cancer and diet.

The latest report also found strong evidence that processed and red meat increase the risk of bowel cancer. This isn’t a new finding, and is something we’ve written about before.

This doesn’t mean you have to be a vegetarian. Too much meat isn’t very good for you but eating it a few times a week probably won’t do much harm. It’s all about balance.

Tried-and-true advice

Beyond diet, this report reinforced the strong evidence that being overweight and drinking too much alcohol also increase the risk of bowel cancer, while being more physically active decreases the risk, adding more weight to previous similar findings.

So our advice remains the same: choose wholegrains and other fibre-rich foods, eat plenty of fruit and veg, keep active, limit your alcohol, and keep a healthy weight.

The science is clear: it’s putting it into practice that’s trickier. We have plenty of hints and tips on our website and we’re also working for better government policy to make being healthier easier for everyone.

Emma Shields is a health information officer at Cancer Research UK