Firstly, what do they mean by processed and red meat?
Red meat is any meat that’s a dark red colour before its cooked – such as beef, lamb and venison, and also pork.
Processed meat is meat that’s not sold fresh, but instead has been cured, salted, smoked and/or processed to enhance flavour or improve preservation (such as added preservatives, especially nitrites – see below). Processed meats include bacon, sausages, hot dogs, ham, salami, pepperoni, highly processed/additive-laden burgers (read the labels) and some types of shop bought pates, as well as meat-based ready meals and tinned meat. Though it doesn’t include fresh, high quality 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 does red and processed meat cause cancer?
Researchers are still trying to find out exactly how red and processed meat causes cancer, though the main culprits seem to be certain chemicals that can be found in meat. These include nitrite preservatives used in processed meats (such as sodium nitrite – read the labels), and also, to a lesser extent natural compounds in red meat. These nitrite compounds are broken down in the gut to form N-nitroso compounds and nitrosamines which are known carcinogens.
Cooking meat at high temperatures, such as grilling or barbequing, can also create chemicals in the meat (heterocyclic amines and polycyclic aromatic hydrocarbons) which are linked to some cancers. Other research suggests that gut bacteria may also play a supporting role.
What are the risks?
There is now a large body of evidence that bowel cancer is more common amongst people who eat the most red and processed meat. There’s also growing evidence for a possible link to both stomach and pancreatic cancers, but this seems to be less clear cut than the link to bowel cancer.
A recent systematic review by the researchers at the World Cancer Research Foundation (WCRF) found that every 100g portion of red meat eaten per day significantly increases your risk of colorectal cancer by 17%, and that every 50g serving of processed meat eaten per day significantly increased the risk by 18%. This equates to a small 5 oz steak or 2 slices of ham. Now, 17% sounds like a large increase in risk, but it is actually relatively small, and in absolute numbers equates to about 66 cases out of 1000 people who eat the most processed meat, compared to 56 cases out of 1000 low-meat eaters – a difference of 10 cases. To put things into perspective, this diagram by Cancer Research UK demonstrates the magnitude of cancer risk from eating processed and red meat compared to smoking.
As what happens so often, the media got the wrong end of the stick. IARC concluded that there is enough scientific evidence to classify processed meat as a ‘definite’ cause of cancer (Group 1 carcinogen – the same group that includes smoking and alcohol), and red meat as a ‘probable’ cause of cancer (Group 2a carcinogen). They did NOT suggest that processed meat causes as much cancer as smoking. This classification shows how confident IARC is that red and processed meat cause cancer, not how much cancer they cause. i.e. they are not reporting on how potent something is in causing cancer – only whether it does so or not. Which is why processed meat has been grouped in the same category as smoking. As summarised in this diagram by Cancer Research UK.
This latest report doesn’t mean that a single meat-based meal is ‘bad for you’. Although regularly eating large amounts of red and processed meat, over a long period of time, is probably not the best for your health and well-being. Red meat is fine in moderation – it can play an important part in a balanced healthy diet and is a great source of quality protein and many nutrients such as B vitamins, iron and zinc. However processed meats, are best avoided or limited, this is for various reasons in addition to increasing your risk of bowel cancer as they also tend to contain high amounts of added salt, artificial additives, refined fats and sugars – all of which have been linked to obesity and chronic disease including heart disease, diabetes, and cancer.
The UK government suggest not eating more than 70g of red or processed meat a day. This can be done by either eating smaller portions of red and processed meat, and by eating these meats less often. However, considering that an 8oz steak is the equivalent of 163g of red meat and 3 rashers of bacon is 73g of processed meat, this is easier said than done. Here is another nifty diagram from Cancer Research UK that shows you just how easy it is for your red / processed meat daily intake to stack up.
Above all, it’s just about being sensible, and not eating too much, too often.