In 2015, the World Health Organization (WHO) classified processed meats as Group 1 carcinogens, citing sufficient evidence that they cause cancer in humans.
Now, a new review challenges this blanket classification, having found that the strength of the evidence varies according to whether the meat contains nitrites.
The International Agency for Research on Cancer (IARC), an arm of the WHO, define processed meat as that which has undergone curing, salting, smoking, fermentation, or some other method of preserving and enhancing flavor.
Examples include frankfurters, bacon, ham, sausages, corned beef, beef jerky, and canned meat.
Some food producers use sodium nitrite to cure processed meat, to enhance color, or as a preservative to increase shelf life.
However, not all processed meats contain nitrites. British and Irish sausages, for instance, are free of nitrites, whereas frankfurters, chorizo, and pepperoni from the United States and continental Europe are not.
Also, in recent years, more nitrite-free processed meats have become available to consumers. These include types of ham and bacon.
Focus on nitrites strengthens the evidence
Researchers from the Institute of Global Food Security, at Queen’s University Belfast (QUB), in the United Kingdom, reviewed recent studies on links between processed meat consumption and cancers of the colon, rectum, and bowel.
They found that only around half the studies concluded that there was evidence of a link with colorectal cancer.
However, that proportion jumped to nearly two-thirds (65%) when they limited their analysis to studies in humans that only involved testing the effects of processed meats containing nitrites.
They report their methods and results in a recent Nutrients study paper.
The team suggests that their findings could explain the conflicting reports in the media about processed meats and cancer risk.
“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,” says first study author William Crowe, Ph.D., of the School of Biological Sciences at QUB.
“Almost two-thirds of studies found a link with cancer”