The World Health Organisation’s controversial blanket classification of processed meat as cancer-causing has been challenged following a major evaluation of global studies by scientists at Queen’s University Belfast (QUB).
The WHO classified all processed meat as carcinogenic in 2015 – including bacon, sausages and ham as well as continental European products such as prosciutto and salami.
However, the QUB researchers found not all processed meats carried the same level of cancer risk, saying nitrite-free processed meat was associated with a lower cancer risk.
British and Irish sausages are not processed with nitrites, though many of the continental and US sausage equivalents are – notably frankfurters, pepperoni and chorizo.
Some newer types of bacon and ham, processed without nitrites, are also appearing on the market.
Dr Brian Green, Dr William Crowe and Prof Chris Elliott from the Institute for Global Food Security at QUB reviewed existing peer-reviewed literature on the relationship between processed meat and development of bowel, colon and rectal cancers. The results of their analysis of a wide range of studies have been published in the journal Nutrients.
They initially reviewed all recent, English-language studies into consumption of processed meat and cancer risk and found results inconclusive – about half the studies evidenced a link with colorectal cancer (CRC). This explains the appearance of contradictory claims in the media in recent years, they conclude.
But when the researchers isolated research which tested only the consumption of processed meat containing sodium nitrite – a preservative used to extend shelf life and enhance colour – evidence of a link with CRC jumped from half to just under two-thirds (65 per cent).
“When we looked at nitrite-containing processed meat in isolation – which is the first time this has been done in a comprehensive study – the results were much clearer,” explained Dr William Crowe. “Almost two-thirds of studies found a link with cancer.”
In its 2015 statement, the WHO did not distinguish between processed meats containing nitrites and those without. Based on the results of their “meta-study”, the researchers now believe there is a need to define the health risk of both types of processed meat separately.
Prof Elliott, who carried out the UK government’s inquiry into the recent horse meat scandal, said their research brought more clarity to what has been a confusing area for the food industry and the public.
Should the public immediately stop eating processed meat containing nitrites? “It’s important we eat a healthy, balanced diet in line with the [UK] government’s ‘Eatwell Guide’,” replied Dr Green.
“The current department of health guidance advises the public to consume no more than 70g of red or processed meat per day. That remains the guidance, but we hope that future research investigating the link between diet and CRC will consider each type of meat individually rather than grouping them together. Our findings clearly show that not all processed meats, for example, carry the same level of risk,” he added.
But based on their study, “what we can confidently say is that a strong link exists between nitrite-containing processed meat, such as frankfurters, and CRC”.
The QUB team intends following up its evidence review with a pre-clinical study probing the effects of nitrite-containing meat on CRC.