Cancer

Processed meat causes colorectal cancer, and red meat probably does

By WhyStopHarmingAnimals.com

Processed meat causes colorectal cancer, and red meat probably does[1]. That is the verdict of the International Agency for Research on Cancer, the World Health Organization's cancer agency, whose 22-expert working group reviewed more than 800 studies[1] before reporting in The Lancet Oncology in 2015. Processed meat went into Group 1, carcinogenic to humans, on sufficient evidence for colorectal cancer[1]. Red meat went into Group 2A, probably carcinogenic[1].

The classification answers whether these meats raise cancer risk. The next question is how much it takes.

How the risk climbs

A 2011 analysis in PLOS One pooled ten prospective cohorts to answer it[2]. Colorectal cancer risk rose 18% for every 50 g of processed meat eaten a day and 17% for every 100 g of red meat a day[2]. The rise ran roughly in a straight line up to about 140 g a day, with no plateau where extra meat stopped mattering[2]. A more recent meta-analysis of red and processed meat intake reached the same conclusion: higher intake raises colorectal cancer risk[3].

What in the meat does it

Heme iron is one mechanism with strong human data behind it[4]. Heme is the iron-carrying pigment that makes red meat red[4], and it can promote the formation of carcinogenic compounds in the colon. Across prospective cohorts covering 566,607 people and 4,734 cases, colon cancer risk was 18% higher at the highest heme-iron intakes than at the lowest[4].

Other mechanisms come from how meat is processed and cooked. Cooking meat at high temperatures produces heterocyclic amines and polycyclic aromatic hydrocarbons, both known carcinogens. Processed meats contain nitrites and nitrates, which can form N-nitroso compounds, which are carcinogenic too.

The plant side

In recent analyses of plant-based diets, vegan patterns come out with the lowest colorectal cancer risk[5]. A 2022 meta-analysis covering 3,059,009 people put plant-based eating at 18% lower risk of digestive-system cancers in cohort studies and 30% lower in case-control studies[6], and colorectal cancer was one of the two clearest signals, alongside pancreatic cancer[6]. A 2025 review of seventeen substitution studies, which look at what happens when animal foods or animal protein are replaced with plant foods, found lower colorectal and breast cancer risk in six of them and no difference in four[7].

The British cohorts are the exception[8]. Pooling two UK cohorts of 61,647 people, researchers found vegetarians had 12% less cancer at all sites combined but no less colorectal cancer[8]. All of these diet comparisons are observational, and they do not agree perfectly on how much protection comes from leaving meat out. The case against the meat itself rests on firmer ground: the IARC review of more than 800 studies[1], the steady dose-response across ten cohorts[2], and heme iron as a mechanism measured in more than half a million people.

What the dose-response curve does say is that there is no amount of processed meat where the risk stops climbing, and the cleanest way to be at the bottom of that curve is to eat none.