Its report said 50g of processed meat a day – less than two slices of bacon – increased the chance of developing colorectal cancer by 18%.
Meanwhile, it said red meats were “probably carcinogenic” but there was limited evidence. The WHO did stress that meat also had health benefits.
Cancer Research UK said this was a reason to cut down rather than give up red and processed meats. And added that an occasional bacon sandwich would do little harm.
Processed meat is meat that has been modified to increase its shelf-life or alter its taste – such as by smoking, curing or adding salt or preservatives.
It is these additions which could be increasing the risk of cancer. High temperature cooking, such as on a barbeque, can also create carcinogenic chemicals.
The WHO has come to the conclusion on the advice of its International Agency for Research on Cancer, which assesses the best available scientific evidence.
It has now placed processed meat in the same category as plutonium, but also alcohol as they definitely do cause cancer.
However, that is not an indication of how much cancer they cause. It does not mean eating a bacon sandwich is as bad as smoking.
“For an individual, the risk of developing colorectal (bowel) cancer because of their consumption of processed meat remains small, but this risk increases with the amount of meat consumed,” Dr Kurt Straif from the WHO said.
Estimates suggest 34,000 deaths from cancer every year could be down to diets high in processed meat.
That is in contrast to one million deaths from cancer caused by smoking and 600,000 attributed to alcohol each year.
Red meat does have nutritional value too and is a major source of iron, zinc and vitamin B12.
However, the WHO said there was limited evidence that 100g of red meat a day increased the risk of cancer by 18%.
The WHO said its findings were important for helping countries give balanced dietary advice.
