Bacon, salami and sausages: how does processed meat cause cancer and how much matters?

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It’s not new news that processed and red meat are linked to bowel cancer. But meat was back in the news last week after research we funded, and press released, took a closer look at how much meat might be enough to increase bowel cancer risk.

The new study, published in the International Journal of Epidemiology, looked at whether people who eat an average of 76 grams of processed and red meat a day – approximately 3 slices of ham – are still at increased risk of bowel cancer. This is similar to the average amount people in the UK eat each day, and falls in a somewhat grey area within government guidelines – which state anyone who eats more than 90 grams a day should cut this to no more than 70 grams a day.

The main takeaway from the study was that even moderate meat-eating increases bowel cancer risk. So, what does this mean for a nation famed for its fry ups?

How do we know processed and red meat cause cancer?

The evidence linking processed and red meat to cancer has been stacking up for over a decade. And in 2015, the International Agency for Research on Cancer (IARC) – a group of experts that review and report on research evidence – classified processed meat as a ‘definite’ cause of cancer.

This places bacon in the same group as tobacco. But IARC groups simply state how certain we can be, based on the evidence, that something causes cancer, not the amount of cancers it causes. This means the evidence that processed meat causes bowel cancer is as strong as it is for tobacco causing cancer, but smoking is responsible for far more cases of cancer than processed meat.

IARC also classified red meat as a ‘probable’ cause of cancer. You can read about this in depth in this blog post we published at the time.

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How does processed and red meat cause cancer?

So far, research has linked three chemicals to increased bowel cancer risk. These chemicals are either naturally found in meat, added during processing or produced when cooking:

• haem (a red pigment found mostly in red meat);
• nitrates and nitrites (used to keep processed meat fresher for longer); and
• heterocyclic amines and polycyclic amines (produced when meat is cooked at high temperatures)

All three can damage the cells in our bowel, and it’s the accumulation of this damage over time that increases cancer risk.

How much matters?

The latest study analysed data from half a million UK adults and found that moderate processed and red meat eaters had a 20% increased risk of bowel cancer compared to low meat eaters. To put this in context, for every 10,000 people on the study who ate 21 grams of red and processed meat a day, 40 were diagnosed with bowel cancer. Eating 76 grams of processed or red meat a day caused 8 extra cases of bowel cancer per 10,000 people.

A 2018 review of the evidence found an increased risk of bowel cancer for every 50 grams of processed meat and 100 grams of red meat someone eats a day.

The latest study looked at even smaller amounts and found an increased risk starting at just 25 grams of processed meat a day, the equivalent of one rasher of bacon. This confirms that no matter how much processed meat you eat, eating less can reduce your bowel cancer risk.

Professor Tim Key, who co-led the recent study and is deputy director at the University of Oxford’s cancer epidemiology unit, says that while the impact of cutting back on processed meat might be smaller than quitting smoking, it’s still important.

“Everyone eats and everyone is at risk of colorectal cancer,” he says. “So any increase in risk makes a difference when we look at the whole population.”

And he sees the results as a reminder for those following government guidelines.

“Current government guidelines suggest if you eat more than 90 grams a day on average you should cut down to 70 grams a day. Our results suggest cutting down a bit more gives slightly lower risk, and are a reminder that there is still an increase in risk for modest intakes of meat.”

What if I have my bacon sandwich on wholemeal bread?

Eating foods high in fibre, especially wholegrains like wholemeal bread or brown rice, and doing lots of physical activity can reduce the risk of bowel cancer – so could this mitigate cell damage from eating processed and red meat?

Both fibre and lots of physical activity help us to poo more often, reducing the amount of time harmful chemicals, including those in processed and red meat, spend in the gut. But so far it’s not clear how much difference this could make to the amount of damage in our cells.

Unfortunately, it’s not as simple as balancing out something that increases risk with something that reduces it. Studies take in to account other things that might impact risk, so good studies that show the link between processed and red meat and bowel cancer will note fibre intake.

What does this mean for me?

The evidence is clear that eating less processed and red meat can help reduce the risk of bowel cancer, the 4th most common cancer in the UK.

“The data from our study does suggest that eating little to no processed and red meat lowers the risk of bowel cancer, but the increased risk at lower intakes is small so this doesn’t imply that everyone needs to give up meat altogether,” says Key.

Cutting down can make a difference, but it’s important to think about doing this as part of a healthy diet overall, along with being active.

“The most important diet related risk factors for cancer are obesity and alcohol, which both increase risk of several types of cancer, and have more impact on risk than red and processed meat,” says Key.

And he notes that diet has other health impacts beyond bowel cancer risk.

“For example, meat can be an important source of iron so if someone is thinking about giving up meat all together they need to think about other sources of this,” he says.

So, although this evidence doesn’t suggest we need to ditch processed and red meat altogether, it does serve as a reminder to think about how much we’re eating, and how often.

Katie Patrick is a health information officer at Cancer Research UK