Αρχική World News How does processed and red meat cause cancer and how much matters?

How does processed and red meat cause cancer and how much matters?

This post was first published in 2019, but has been reviewed and updated in March 2021.

It’s not new news that processed and red meat are linked to bowel cancer. But in 2019, Cancer Research UK scientists took a closer look at how much meat might be enough to increase bowel cancer risk.

The 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?

What are ‘red’ and ‘processed’ meat?

First, let’s clear up some definitions.

‘Red’ meat is (as you might expect), any meat that’s a dark red colour before it’s cooked – this obviously means meats like beef and lamb, but also includes pork.

‘Processed’ meat is meat that’s not sold fresh, but instead has been cured, salted, smoked, or otherwise preserved in some way (so things like bacon, sausages, hot dogs, ham, salami, and pepperoni). But this doesn’t include fresh burgers or mince.

Both of these types of meat are distinct from ‘white’ meats, like fresh chicken or turkey, and fish (neither of which appear to increase your risk of cancer).

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 (or Group 1 carcinogen) – the same group that includes smoking and alcohol. And red meat is a ‘probable’ cause of cancer (or a Group 2a carcinogen) – the same group as night shift work.

Meat and cancer risk

Copy this link and share our graphic. Credit: Cancer Research UK

While this may sound alarming, it’s important to remember that these groups show how confident IARC is that red and processed meat cause cancer, not how many cancer cases they cause, as we wrote when we covered a previous IARC decision on diesel emissions, and interviewed one of our experts in the causes of cancer.

As Professor David Phillips – a Cancer Research UK-funded carcinogen expert from King’s College London – explains, “IARC does ‘hazard identification’, not ‘risk assessment’.

“That sounds quite technical, but what it means is that IARC isn’t in the business of telling us how potent something is in causing cancer – only whether it does so or not”, he says.

To take an analogy, think of banana skins. They definitely can cause accidents, explains Phillips, but in practice this doesn’t happen very often (unless you work in a banana factory). And the sort of harm you can come to from slipping on a banana skin isn’t generally as severe as, say, being in a car accident.

But under a hazard identification system like IARC’s, ‘banana skins’ and ‘cars’ would come under the same category – they both definitely do cause accidents.

To put things in perspective, let’s look at how processed meat stacks up against smoking.

Tobacco vs meat - what's the risk?

Copy this link and share our graphic. Credit: Cancer Research UK

How does processed and red meat cause cancer?

So far, research has linked 3 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 3 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 over almost 7 years and found that moderate processed and red meat eaters – those eating 79g per day on average – had a 32% increased risk of bowel cancer compared to people eating less than 11g of red and processed meat daily.

To put this in context, for every 10,000 people on the study who ate less than 11 grams of red and processed meat a day, 45 were diagnosed with bowel cancer. Eating 79 grams of red and processed meat a day caused 14 extra cases of bowel cancer per 10,000 people. These figures are just for the independent effect of meat consumption, as they take into account other differences between these groups of people, for example sex, deprivation, smoking, physical activity, alcohol intake, other aspects of diet, reproductive factors, and body mass index.

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.”

Top tips for cutting down

  • Pay attention to your portions – try having 1 sausage instead of 2 or switching half of the meat in your usual dishes for beans or veggies.
  • Have meat free days – pick a day (or days) to have no meat at all.
  • Get out of a recipe rut – look for new recipes that use fresh chicken or fish instead of processed and red meat.

What if I have my bacon sandwich on wholemeal bread?

Having a diet high in fibre, especially wholegrains, found in foods like wholemeal bread or brown rice, and doing lots of physical activity can is associated with lower 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 and many other factors which can be associated with both cancer risk and meat 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.

Eating less 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 many types of cancer, and cause more cases 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

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