The World Health Organisation (WHO) says processed meats - such as bacon, sausages and ham - do cause cancer.
It said eating processed meat can cause bowel cancer in humans while red meat is a likely cause of the disease - a statement likely to sharpen debate over the merits of a meat-based diet.
The International Agency for Research on Cancer (IARC), which is part of the WHO and based in Paris, put processed meat like hot dogs and ham in its group 1 list, which already includes tobacco, asbestos and diesel fumes, for which there is "sufficient evidence" of cancer links.
Red meat, under which the IARC includes beef, lamb and pork, was classified as a "probable" carcinogen in its group 2A list that also contains glyphosate, the active ingredient in many weedkillers.
The lower classification for red meat reflected "limited evidence" that it causes cancer. The IARC found links mainly with bowel cancer, but also observed associations with pancreatic and prostate cancer, it said.
Cancer Society medical director Chris Jackson told Morning Report processed meat is smoked, salted or preserved, which may be what's involved in the carcinogenesis.
"Sunlight is a grade 1 carcinogen as well, but I don't think we would say you should avoid the sun, because there are sun health benefits. It does mean, however, you should avoid the sun between 10 and 4 and wear sunscreen
"And similarly there are health benefits from consuming meat - it has zinc, B12 as well as a good source of protein."
A nutritionist with the Meat Processors' Association Fiona Grieg said New Zealanders eat about 22 grams a day of processed meat on average.
She said there was no evidence eating moderate portions was bad for you.
"I'm comfortable in saying that both meat and processed meat in moderate portions can be included as part of a diet as long as there's plenty of vegetables and whole grains in that diet to reduce cancer risk."
Executive Officer of Bowel Cancer New Zealand Fiona Colbert said while she was shocked to hear that processed meat was such a high risk, more information was needed on how much was safe to eat.
She said families should not completely eliminate it to avoid cancer, but consider having meat-free days each week to lower their risk.
"We do have to bear in mind that we could actually start looking at everything as being unhealthy for us...it's about having everything in moderation and ensuring you have a healthy lifestyle."
The IARC was carrying out a formal review of meat for the first time and examined some 800 studies during a meeting of 22 health experts in France earlier this month.
Each 50 gram portion of processed meat eaten daily increased the risk of colorectal cancer by 18 percent, the agency estimated.
The IARC does not compare the level of cancer risk associated with different substances in a given category, so does not suggest eating meat is as dangerous as smoking, for example.
But the bracketing of processed meat with products such as tobacco or arsenic irked industry groups, with the North American Meat Institute saying the IARC report "defies common sense".
Suppliers argue that meat provides essential protein, vitamins and minerals as part of a balanced diet.
The IARC said an estimate from the Global Burden of Disease Project - an international consortium of more than 1000 researchers - showed that 34,000 cancer deaths per year worldwide were attributable to diets high in processed meat.
This compared with about 1 million cancer deaths per year globally due to tobacco smoking and 600,000 a year due to alcohol consumption, it said.
Risk of tobacco vs meat graphic from Cancer Research UK "processed and red meat 3% of all cancers, tobacco 19%" pic.twitter.com/wRJ0kpBOxS— George Laking (@glaking) October 26, 2015
why is everyone talking about bacon? sausage is the real heartbreaker from today's news.— Anna Sale (@annasale) October 26, 2015
First they came for tobacco, and i never spoke up, but then they came for bacon and small goods and i'm like HEY STEADY ON THERE SCIENCE!— Te Radar (@teradar) October 26, 2015
This Bacon & Sausages Will Kill You! story is melodramatic journalism at best Old age will also kill you And getting hit by a car— Grumpy (@GrumpyYetAmusin) October 26, 2015
According to these new studies, that bacon will be being taken from my cold dead hands a few years sooner than I'd like.— David Slack (@DavidSlack) October 26, 2015
Relax. In a few years the Wheel of Food Panic will turn, "moderate" amounts of bacon will be "safe" and kale will be "linked to" cancer.— Stephanie Rodgers (@bootstheory) October 26, 2015