Disclaimer: not a nutritionist, so take what I'm going to say with a huge pinch of (blood-pressure raising) salt.
I found two summaries of the evidence on the link between colorectal cancer and red meat consumption. Both are 5 years old now, so there might well be more up to date evidence available.
Firstly, there is this report from the Continuous Update Project. It looked at 7 studies to show a 17% increased risk of cancer per 100g of red meat consumed per day (RR: 1.17 (1.05-1.31)).
For processed meat, it is worse. 9 studies were looked at and these suggested that eating processed meat increases the risk of bowel cancer by 18 per cent per 50g processed meat per day (RR 1.18 (1.10-1.28)).
www.wcrf.org/int/research-we-fund/continuous-update-project-findings-reports/colorectal-bowel-cancer
- The Iron and Health report from 2011 which has a bit of a literature review on colorectal cancer and red meat, which looks at a larged number of studies. You can see the whole report here, but I've excerpted the most relevant parts below: www.gov.uk/government/uploads/system/uploads/attachment_data/file/339309/SACN_Iron_and_Health_Report.pdf
Red meat intake and colorectal cancer risk (Annex 7, Table A18)
Twenty-one prospective studies have been published since 1996 (including some updated analyses from previously published cohorts). Two of these studies (Balder et al, 2006; Sato et al, 2006) considered the risk of colorectal cancer with total meat consumption rather than only red meat. Twenty-one out of the 25 relative risks reported were greater than one, 3 significantly so (Chao et al, 2005; Larsson et al, 2005; Cross et al, 2007). The median relative risk for highest versus lowest red meat intake was 1.17. The increased relative risk was statistically significant in 1 out
of the 4 largest studies (Wei et al, 2004; Chao et al, 2005; Norat et al, 2005; Crosset al, 2007); the trend was statistically significant in 2 of the 4 studies and close to significance in 1 study.
7.58 Significantly increased colorectal cancer risk was associated with red meat intakes of ≥ 114 g/day for men, ≥ 80 g/day for women (Chao et al, 2005); ≥ 94 g/day (Larsson et al, 2005); and 62.7 g per 1000 kcal (equivalent to 145 g/day for men and 102 g/day for women62) (Cross et al, 2007). In all the studies which reported a significantly increased risk of colorectal cancer, processed meat was included under the category
of red meat.
Processed meat intake and colorectal cancer risk (Annex 7, Table A19)
7.59 Fourteen prospective studies have been published since 1996 (including some updated analyses from previously published cohorts). Thirteen out of the 18 relative risks for highest compared to lowest processed meat intake were greater than 1; of these, 5 were significant (English et al, 2004; Wei et al, 2004; Norat et al, 2005; Oba et al, 2006; Cross et al, 2007). The median relative risk was 1.16. The relative risk was statistically significant in 3 out of the 4 largest studies (Wei et al, 2004; Chao et al, 2005; Norat et al, 2005; Cross et al, 2007), and the trend was statistically significant in all the studies.
7.60 Increased colorectal cancer risk was significantly associated with processed meat intakes of ≥ 20.3 g/day (Oba et al, 2006); ≥ 29 g/day (English et al, 2004); ≥ 80 g/day (Norat et al, 2005); 22.6 g per 1000 kcal (equivalent to 52.3 g/day for men and 36.9 g/ day for women) (Cross et al, 2007); and 5 times per week or more (Wei et al, 2004).
Colorectal cancer risk in vegetarians
7.61 A pooled analysis (Key et al, 2009a) of individual participant data (n=61,566) from 2 studies in the UK which examined cancer incidence in vegetarians (Sanjoaquin et al, 2004; Key et al, 2009b) observed no significant difference in colorectal cancer incidence between meat eaters and vegetarians (relative risk in vegetarians compared to meat eaters = 1.12; 95% CI, 0.87–1.44) after 12 years of follow-up. However, the analysis did not fully characterise meat consumption patterns and
the total meat intake of non-vegetarians was much lower than the average UK intakes of meat consumers reported in the National Diet and Nutrition Survey (Henderson et al, 2002).