by Jack Norris, Registered Dietitian
Dunneram et al. (2026) conducted a meta-analysis of cancer incidence among nine cohorts that included a large number of vegetarians. It found a higher rate of colorectal cancer among vegans.
I’ve added details about the study to the section, Specific cancer incidence among vegans of Cancer and Vegan Diets. I’ve excerpted the Summary here:
A meta-analysis by Dunneram et al. (2026) found higher risks of colorectal cancer in vegans, driven in part by rectal cancer. After removing the first four years of follow-up, the colorectal finding attenuated and was no longer statistically significant, consistent with potential reverse causation or inclusion of early cases. However, a higher rate of rectal cancer for vegans remained statistically significant even after removing the first four years of follow-up and among never smokers.
The overall lower rates of cancer seen among vegans in the AHS-2 and British vegetarian cohorts, should still give vegans an overall benefit in terms of cancer. However, it’s worth monitoring these findings. Vegan case numbers were small (e.g., rectal n≈35 across cohorts), so estimates are imprecise.
In AHS-2 and the British vegetarian cohort, vegans had lower overall cancer incidence; these cohorts suggest vegans tend to have lower overall cancer risk, even though site-specific trends vary.
In the British cohort, colorectal cancer in vegans wasn’t significantly different from regular meat-eaters but trended higher (RR 1.31, 95% CI 0.82–2.11). In AHS‑2, vegans trended lower for colorectal (HR 0.88, 95% CI 0.64–1.22) and higher for rectal (HR 1.13, 95% CI 0.60–2.13), both nonsignificant.
In Dunneram et al.’s meta-analysis, lacto‑ovo‑vegetarians had similar colorectal cancer rates as regular meat‑eaters; pescatarians had lower colon cancer, including after excluding the first four years and among never-smokers. This pattern could reflect nutrient differences; Dunneram et al. noted that vegans had the lowest average calcium and lower long‑chain omega‑3 intakes across cohorts.
We don’t want to be alarmist—the statistics here aren’t strong, and observational data can’t prove causation. We already urge vegans to meet calcium needs with fortified foods (and supplement if needed). I’m more hesitant to recommend universal EPA/DHA supplementation, but the rectal-cancer signal has me re‑evaluating. I’ll be reviewing the EPA/DHA evidence in more depth.
Stay tuned!
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