Nitrates are in the news again after French health authorities confirmed a link between additives in processed meats and bowel cancer.
France’s national food safety body now recommends reducing the consumption of nitrates and nitrites found in processed meats such as prosciutto, bacon and chorizo.
What are these compounds, and does the finding mean Australians should forgo their next charcuterie board?
What are nitrates and nitrites?
Nitrates (NO3-) and nitrites (NO2-) are compounds commonly found in a wide variety of foods, including vegetables such as spinach, carrot and beetroot.
They are also added to meat products and some cheeses as a preservative, in the form of sodium or potassium salts. As an additive, their main purpose is to prevent the growth of Clostridium botulinum, bacteria that produce the potent and potentially deadly botulinum toxin – commonly known as botox.
In 2015 the World Health Organisation’s International Agency for Research on Cancer said there was enough evidence of a causal link with bowel cancer – also known as colorectal cancer – to classify processed meats as group 1 carcinogens, in the same category as asbestos and tobacco smoking. (Although they are in the same category, it does not mean that these carcinogens are equally dangerous.)
The agency’s experts concluded at the time that the risk of colorectal cancer increased by 18% for each 50g portion of processed meat eaten daily.
Not all ingestion of nitrites and nitrates has the same effect – we get most of our intake from fruit and vegetables, foods with a lower risk of cancer. In Australia, processed meats account for less than 10% of total dietary exposure to nitrites, according to research conducted by Food Standards Australia and New Zealand (FSANZ) in 2011.
Nitrates can be converted into nitrites by bacteria in our mouths. “It’s nitrites, rather than nitrates, that are related to cancer,” nutritionist Dr Rosemary Stanton says.
“Nitrites can react with protein fragments that are left over after proteins are digested – the proteins from meat are the major culprits here, especially haem, the protein that carries iron in red blood and [is] found in meat, but not in plant products.
“These fragments and protein remnants form molecules known as N-nitroso compounds (NOCs). These are the problem in causing cancer, and the problem is most likely to occur in the colon, but especially from meats processed using sodium nitrite,” Stanton says.
“Problems with nitrates and nitrites also depend on other factor: the nitrates in foods can be changed by bacteria in saliva, by acid in the stomach, the vitamin C in the product – [a] relevant protective factor for vegetables – and the NOCs that get to the large bowel after digestion.”
FSANZ says on its website the risk in Australia is low.
“Australian consumers should be reassured that exposures to nitrates and nitrites in foods are not considered to represent an appreciable health and safety risk. The health benefits of fruit and vegetables are widely accepted, and eating these foods is recommended as part of a balanced diet.”
How much of these additives are in processed foods in Australia?
There are regulations in Australia on the amounts that can be added to processed foods – a maximum of 50 mg/kg of nitrates for cheese products, and no more than 125 mg/kg total nitrates and nitrites for cured meat.
A 2008 study that analysed the nitrite and nitrate content of cured meats in Australia found they were “below the regulatory limits” set by FSANZ.
It estimated the average Australian intake of nitrates to be 267mg per adult a day, and 5.3mg of nitrites.
How much processed meat should I be eating?
“In Australia, processed meats are regarded as what we call discretionary foods”, Stanton says – meaning they are not in the five food groups identified in the Australian Guide to Healthy Eating.
The Australian dietary guidelines state that “consuming processed meat may be associated with an increased risk of colorectal cancer” and encourage people to limit their intake of such products to once a week or less.
“It doesn’t mean you can never have bacon and eggs,” Stanton says. “But processed meat should not be a regular part of the diet – it should be just an occasional thing.”
FSANZ has been contacted for comment.