A recent column on the health risks of processed meat has sparked a slew of questions from concerned readers.
Answer: Ham, bacon, pastrami and salami, along with sausages, bratwursts, frankfurters, hot dogs, corned beef and beef jerky, are all categorised as processed meat because of the way they’re made. To explain, the International Agency for Research on Cancer (IARC) defines processed meat as “meat that has been transformed through salting, curing, fermentation, smoking or other processes to enhance flavour or improve preservation. Most processed meats contain pork or beef, but processed meats may also contain other red meats, poultry, offal or meat by-products such as blood.”
There’s little point in telling us of this increased health risk without telling us what the actual risk is of eating processed meat – for example, is it greater or less than the risk of being killed or injured in a motor vehicle accident, a risk we all accept every day?
"Colorectal cancer is not trivial, it was the fifth leading cause of death in New Zealand in 2015,” says Professor Nick Wilson, a public health physician who co-authored a recent review of the impact of red meat and processed meat on New Zealanders’ health.
Wilson and colleagues at the University of Otago estimate that for each 50 grams of processed meat eaten daily (for example, one or two rashers of bacon), a non-Maori male would lose on average 16 days of life expectancy due to the increased risk of colorectal cancer linked to processed meat intake. While that may sound insignificant, bear in mind it’s an average, with most people losing no life expectancy but a few potentially losing decades from dying of bowel cancer in their fifties, says Wilson.
Sir David Spiegelhalter, a risk professor at Cambridge University, summarised the processed-meat colorectal-cancer risk for UK residents in different terms: about six in every 100 people are expected to get bowel cancer at some stage. If all those people ate 50 grams of processed meat every day of their life, we would expect 18% more to get bowel cancer – which is a rise from six cases to seven cases. “So that’s one extra case of bowel cancer in all those 100 lifetime bacon eaters.”
However, these examples don’t take into account the increase in cases of type 2 diabetes and cardiovascular disease linked to eating processed meat. What’s more, the incidence of colorectal cancer in New Zealand is high by international standards. In 2008, there were 44.1 cases reported per 100,000 males and 37.5 per 100,000 females, compared with just 36.2 cases and 23.5 cases per 100,000 for males and females respectively in the UK. So the actual health risk in New Zealand for processed meat eaters is likely to be greater than the above examples.
On the other hand, reducing our overall dietary salt intake would have a greater impact on our health than reducing processed meat intake. One New Zealand study found that reducing dietary salt would give an extra 44 days of life per adult on average.
Overall, dietary risks are the leading risk factor for death and disability in New Zealand, according to an analysis by the Institute of Health Metrics and Evaluation. So an average New Zealander wishing to improve their health and life expectancy should definitely focus on improving their diet, whereas a smoker should make quitting a priority, says Wilson.
What exactly in “processed” meats gives rise to the health risks? Is it the fat content, the preservatives or the smoking process?
“The nitrates, which give processed meats their pink colour, are an important part of the cancer risk,” says Wilson. Nitrite is used to preserve processed meats – it is extremely toxic to bacteria – but it can react with compounds during the curing process of meat or in our body to produce N-nitroso compounds, several of which are known human or animal carcinogens. Plus the high salt content of processed meats, along with how the meat gets cooked – for example, burning of sausages – is also likely to contribute to their cancer risk, says Wilson.
However, other less-clear factors are probably also relevant, he says. For example, the IARC classified red meat as “probably carcinogenic to humans”, based on limited evidence that red meat may cause colorectal cancer in humans and strong evidence of a biologically plausible path for this. Red meat has also been linked to pancreatic and prostate cancers. Notably, poultry and fish are not linked to bowel cancer, says Wilson. So part of the issue with processed meat may stem from the fact it’s typically derived from red meat. However, the positive health benefits of lean red unprocessed meat are worth considering when it’s eaten in limited amounts; it’s a valuable, but not essential, source of protein, iron, zinc and vitamin B12.
Would making my own sausages (containing nothing but finely minced meat) or buying my butcher’s organic or natural sausages be considered safe?
Answer: If the sausages contained no added nitrates, that’s definitely a positive, says Wilson. However, there is still the possibility of salt being added to these ‘natural products’, he says, “and there will be those other factors that make fish and poultry safer”.
Might the problem be one for the commercial meat processors – if they processed their product differently, would we be safer?
“They could do more by reducing levels of preservatives and salt,” says Wilson, who notes that some producers are already working to reduce salt levels in their processed meat products. But ultimately, it’s up to consumers to choose whether they want to eat processed meat, and accept the inevitable health risks; other protein-rich foods such as fish, which can offer health benefits; or soy-protein alternatives, “which are healthier and also better for the environment”.
Does smoked salmon fall into the same category as processed meat?
No, but there is some evidence that smoking of food is not so good, as it’s associated with the formation of polycyclic aromatic hydrocarbons (PAHs). A number of PAHs are classified as possible or probable human carcinogens, and evidence has linked consumption of smoked animal meats to stomach cancer.
Does tinned fish such as sardines fall under the same category as processed meat?
“There is no clear evidence that tinned or fresh fish is associated with cancer risk – and fish probably helps to prevent heart disease,” says Wilson.
This article was first published in the May 6, 2017 issue of the New Zealand Listener.