Processed Meat & Colorectal Cancer Risk

This page explains what the research on processed meat and colorectal (bowel) cancer really shows, in plain numbers. It also covers what the labels from IARC, the World Health Organization's cancer research agency, mean and where diet fits next to screening.

You have probably seen the headline: processed meat raises colorectal cancer risk by 18 percent. That figure is real, and it is almost always reported without the thing that makes it meaningful.

Eighteen percent is a relative increase, and it applies to each 50 g of processed meat eaten every day. That is a daily habit sustained over time.

Here is the same fact in absolute terms. In the US, about 3.9 percent of people are diagnosed with colorectal cancer at some point in their lives. That is the NCI SEER figure. Raising that by 18 percent gives roughly 4.6 percent. The difference is about seven extra cases per 1,000 people over a lifetime, for the group eating that much processed meat daily. Real, worth knowing, and a very different impression from what the headline creates.

In 2015, IARC classified processed meat as Group 1, carcinogenic to humans (able to cause cancer in people), based on sufficient evidence that it causes colorectal cancer. It classified red meat as Group 2A, probably carcinogenic to humans, based on limited evidence. For red meat, IARC noted that if the association proves causal, each 100 g eaten daily would raise colorectal cancer risk by about 17 percent.

Processed meat means meat transformed by salting, curing, fermentation, smoking or similar processes: bacon, ham, sausages, hot dogs, salami, corned beef, jerky. Red meat means all mammalian muscle meat, including beef, veal, pork, lamb, mutton, horse and goat.

This is the single most misread thing about the classification, and IARC addressed it directly. The Group labels describe the strength of the scientific evidence that an agent can cause cancer, rather than assessing the level of risk. Being in Group 1 means the evidence that something can cause cancer is strong, not that the danger matches every other Group 1 agent.

The numbers show the gap. IARC cites a Global Burden of Disease Project estimate that about 34,000 cancer deaths worldwide each year are attributable to diets high in processed meat. IARC says the Group labels are about how strong the evidence is, not how large the risk is at a given amount.

IARC concluded that the evidence did not permit a conclusion about whether a safe level exists. What it could say is that risk rises with the amount consumed.

Beyond that, this page cannot give a safe number. Ask your care team what is reasonable for you. Risk builds over years of habit. One meal is not a verdict, and it is not a reason to feel that damage has been done.

If colorectal cancer is what worries you, the thing that moves the needle most is not on your plate. It is screening. The CDC says screening tests can find polyps so they can be removed before they turn into cancer. Most people should begin screening at age 45, and some need to start earlier. Ask your care team when to start and which test suits you.

Cutting back on processed meat is a reasonable, low-cost change. It works best as one step among several rather than the whole plan.

If you want to shift without feeling deprived, move processed meat from daily to occasional rather than cutting it out. Use poultry, fish, eggs, beans and lentils in the places where bacon and deli meat currently sit. Gradual and sustainable beats strict and abandoned.

• IARC — Q&A on the carcinogenicity of red meat and processed meat (Volume 114)
• NCI SEER — Colorectal Cancer Stat Facts (lifetime risk)
• CDC — Colorectal cancer screening
• WHO — Q&A on red and processed meat