High consumption of processed meat such as sausage and ham is consistently associated with an 18 to 21% greater risk of colorectal cancer. This is one of the most robustly supported associations in nutritional research, although the evidence is largely associative. Eating less processed meat and more fibre is the most logical preventive step.
Processed meat such as sausage, ham, salami and bacon has been consistently and significantly linked to an increased risk of colorectal cancer (colon and rectum combined) in multiple large meta-analyses. When comparing people who eat a lot of processed meat with those who eat little, the risk of colorectal cancer is on average 18 to 21% higher. For every additional 50 grams of processed meat per day, the risk rises by approximately 18%. This is one of the most robustly supported associations in nutritional research. (PMID: 34455534, 40210826, 21674008, 33838606)
For colon cancer specifically, the evidence is strongest and most consistent, with elevated risks of 13 to 21% across multiple independent large analyses. For rectal cancer separately, the picture is somewhat less consistent: most recent studies also find an elevated risk of 17 to 22% there, but an older meta-analysis found no statistically significant association for rectal cancer on its own. (PMID: 40210826, 34455534, 21674008)
These are statistical associations from observational research, not proven causality of the kind you would have from a controlled experiment. People who eat a lot of processed meat may also live differently in other ways. Researchers adjust for many such factors, but this can never be fully ruled out. Nevertheless, the World Health Organization classifies processed meat as a 'Group 1 carcinogen', meaning there is sufficient evidence to consider a causal relationship probable.
A biological explanation is also available. Gut bacteria convert proteins and fats from meat into substances that promote inflammation and may damage intestinal cells. A diet low in fibre and high in meat disrupts the balance in the gut: fibre normally promotes the production of butyrate, a substance that protects intestinal cells. Less fibre and more meat can reduce this protective effect. (PMID: 27848961, 25575572)
Processed meat is not the only culprit. A study of more than 142,000 people found that high consumption of ultra-processed food in general, including but not limited to processed meat, is associated with approximately 18 to 20% greater odds of colorectal polyps. These are the precursors to colorectal cancer. Even when processed meat is removed from the calculation, this association persists, indicating that other ultra-processed products also contribute. (PMID: 36477589)
Cutting back on processed and red meat and eating more fibre is considered a meaningful preventive step. Estimates from epidemiological research suggest that roughly half of the colorectal cancer risk can be influenced through lifestyle, including diet. Whether targeted dietary interventions in people at elevated risk actually prevent colorectal cancer has been less well demonstrated in controlled trials. The available data come largely from observational research. (PMID: 33518157, 25575572, 27848961)
Based on multiple large meta-analyses of prospective studies (tens to hundreds of studies per meta-analysis), supplemented by mechanistic research into the gut microbiome and one large cohort study on ultra-processed food and polyps. The associations are consistent, but the causal evidence is largely observational in nature.