Processed meat can lead to colorectal cancer, and eating red meat is probably cancer-causing as well, the World Health Organization's cancer agency said Monday.

In a new report, the France-based International Agency for Research on Cancer (IARC), classified processed meat -- such as hot dogs, bacon and ham – as “carcinogenic to humans.” IARC said it made its decision because there is "sufficient evidence" that processed meat is linked to cancer.

Red meat meanwhile – which includes beef, lamb and pork -- was classified as a "probable" carcinogen, and placed into IARC’s group 2A. It said red meat was linked to colorectal cancer, as well as to prostate and pancreatic cancer.

IARC’s Dr. Kurt Straif said in a statement that the risk of developing colorectal cancer after eating small amounts of processed meat is likely low, but “this risk increases with the amount of meat consumed.”

A working group of 22 experts from 10 countries said they evaluated more than 800 studies from several continents about meat and cancer before reaching their conclusions.

The group said it looked at links between more than a dozen types of cancer and the consumption of red or processed meat in many populations with diverse diets. The most “influential evidence” came from large studies conducted over the past 20 years, it said.

Its findings support current recommendations from several governments and public health groups to limit the intake of red and processed meat. The Canadian Cancer Society, for example, has long said research has shown a link between colorectal cancer and a diet high in red and processed meat.

Still, Dr. Christopher Wild, the director of IARC, noted that red meat has nutritional value, so it will be up to governments and international regulatory agencies to conduct risk assessments, to help consumers balance the risks and benefits of eating red meat and processed meat.

IARC said processed meat refers to meat that has been transformed through salting, curing, fermentation, smoking, or other processes. Examples include hot dogs, ham, sausages, corned beef, and beef jerky.

Same category as smoking but not same risk

IARC classifies carcinogens into five categories ranging from “carcinogenic” (Group 1) to “probably not carcinogenic” (Group 4). Group 1 carcinogens include tobacco, asbestos and diesel fumes, while Group 2a also contains the weedkiller glyphosate and the insecticide diazinon.

IARC noted that although processed meat has been placed in the same category as smoking and asbestos, that does not mean they are equally dangerous. Instead, the classifications describe the strength of the evidence about an agent being carcinogenic, rather than its level of risk.

The North American Meat Institute (NAMI) responded to the report by saying that classifying red and processed meat as cancer hazards “defies common sense.”

They also said that numerous studies have shown that cancer is a complex disease not caused by single foods and that a balanced diet and healthy lifestyle choices are essential to good health.

How much is safe?

As for how much meat is a safe amount, the IARC authors say there is not yet enough evidence to draw any conclusions on that except to say the risk increases with the amount of meat consumed.

The Canadian Cancer Society says that based on the most recent evidence, adults should try to limit red meat to 3 servings per week, adding that these recommended servings may differ depending on your age and gender.

A serving of meat is considered to be 85 grams, or 3 ounces, after cooking. That is slightly smaller than a deck of cards.

The IARC experts estimate that eating 50 grams of processed meat daily -- the equivalent of one hot dog or one to two slices of deli meats -- increases the risk of colorectal cancer by 18 per cent. But for many people, that is a small risk increase, says Toronto-based Internal medicine specialist Dr. Shawn Wharton.

“If your risk is already small, an 18 per cent increase is not a big one,” he told CTV News Channel.

“The risk of colon cancer for the average person is about five per cent, but if you have a family history of it, then your risk is much higher.”

Other risk factors for colorectal cancer include: being overweight and sedentary; having a low-fibre diet; and drinking alcohol. Men are more likely than women to develop colorectal cancer, and the risk increases with age.

The risks of red and processed meat

It’s not clear why red and processed meat increase the risk of cancer but the Canadian Cancer Society says some possibilities include:

  • Dietary heme iron, which has been shown to cause damage to the colon lining and promotes increased cell growth.
  • Cooking meat at high temperatures such as barbecuing and broiling produces chemicals called heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs), which may increase cancer risk.
  • Nitrates and nitrites are chemicals, added as a preservatives in processed meat, which can contribute to the formation of nitrosamines and nitrosamides, which may be carcinogenic.