What the evidence suggests
The upshot is: the evidence supports the classification of processed meats as a definite cause of cancer, and red meat a probable cause. This was most strongly associated with colorectal cancer, but also linked to pancreatic, prostate and stomach cancers.
Processed meat is meat that has been salted, cured or smoked (or other preservation process such as fermentation). This include things like bacon, hot dogs, ham and jerky. Most processed meats contain pork or beef, but may also contain other red meats, poultry, offal, or meat by-products such as blood.
Red meat is meat that’s dark red in colour before cooking and refers to all mammalian muscle meat, including, beef, veal, pork, lamb, mutton, horse and goat.
How does it cause cancer?
The ‘how’ is not fully understood, but is thought to be linked to chemicals found in the meat itself, how these change during the process of cooking, how our body reacts to these during the process of digestion, as well as the health of our gut bacteria.
High temperature cooking in particular – such as grilling or barbequing – generates compounds that may increase the risk of cancer, and tend to be produced in higher levels in red and processed meat compared to other meats. Even so, their role in the progression of cancer is not entirely clear.
How much is too much?
The evidence doesn’t point to a specific amount of meat that’s healthy or, conversely, too much. What is apparent from the literature is that the risk generally increases with the amount of meat consumed. So, the more you eat, the greater the risk.
Data analysis suggests that every 50gm portion of processed meat eaten daily increases the risk of colorectal cancer by about 18%; and every 100gm portion of red meat eaten daily could increase risk by 17%. To put this in perspective, two rashers of bacon or slices of ham is around 50g or processed meat, while a small-average steak is around 100g of red meat. The Cancer Council suggests consuming no more than 455g of lean red meat per week, but makes no recommendations about processed meats.
So, stop eating meat and I won’t get cancer?
It’s not as simple as that. And, as many people pointed out when the report was released, there are numerous factors implicated in the development of cancer (such as genetics and alcohol intake) and some that pose a significantly higher risk (such as smoking).
Nonetheless, if you have a very meat-heavy diet, it’s worthwhile cutting down on how much you’re eating and consider other protein sources to include in your meals, such as chicken and fish, tofu and legumes. While you’re at it, take a look at what other risks you are exposing yourself to that are associated with cancer, such as smoking and alcohol consumption.
All up, these findings do not present new information – the evidence has been building for decades – but should attract our attention and remind us of the ‘everyday’ risks we expose ourselves to in our diet and lifestyle. There really can be too much of a good thing.
You can read the full summary of findings in the December 2015 issue of The Lancet Oncology.