Risk of cancer in regular and low meat-eaters, fish-eaters, and vegetarians: a prospective analysis of UK Biobank participants
Authors: Watling Cody Z. , Schmidt Julie A. , Dunneram Yashvee , Tong Tammy Y. N. , Kelly Rebecca K. , Knuppel Anika , Travis Ruth C. , Key Timothy J. , Perez-Cornago Aurora 
Published: September 2021

Background

Following a vegetarian diet has become increasingly popular and some evidence suggests that being vegetarian may be associated with a lower risk of cancer overall. However, for specific cancer sites, the evidence is limited.

Aim

To assess the associations of vegetarian and non-vegetarian diets with risks of all cancer, colorectal cancer, postmenopausal breast cancer, and prostate cancer, and to explore the role of potential mediators between these associations.

Methods

We conducted a prospective analysis of 472,377 UK Biobank participants who were free from cancer at recruitment. Participants were categorised into regular meat-eaters (n=247,571), low meat-eaters (n=205,385), fish-eaters (n=10,696), and vegetarians (n=8,685) based on dietary questions completed at recruitment. Multivariable-adjusted Cox regressions were used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for all cancer incidence and separate cancer sites across diet groups.

Results

After an average follow-up of 11.4 years, 54,961 incident cancers were identified, including 5,882 colorectal, 7,537 postmenopausal breast, 9,501 prostate cancer cases. Compared with regular meat-eaters, being a low meat-eater, fish-eater, or vegetarian were all associated with a lower risk of all cancer (HR: 0.98, 95% CI: 0.96-1.00; 0.90, 0.84-0.96; 0.86, 0.80-0.93, respectively). Being a low meat-eater was associated with a lower risk of colorectal cancer in comparison to regular meat-eaters (0.91, 0.86-0.96); there was heterogeneity in this association by sex (p=0.007), with an inverse association across diet groups in men, but not in women. Vegetarian postmenopausal women had a lower risk of breast cancer (0.82, 0.68-0.99), which was attenuated and non-significant after adjusting for body mass index (BMI; 0.87, 0.72-1.05); in mediation analyses, BMI was found to possibly mediate the observed association. In men, being a fish-eater or a vegetarian was inversely associated with prostate cancer risk (0.80, 0.65-0.99 and 0.69, 0.54-0.89, respectively).

Conclusion

Low and non-meat-eaters had a lower risk of being diagnosed with cancer in comparison to regular meat-eaters. We also found that low meat-eaters had a lower risk of colorectal cancer, vegetarian women had a lower risk of postmenopausal breast cancer, and vegetarians and fish-eaters had a lower risk of being diagnosed with prostate cancer. The lower risk of colorectal cancer in low meat-eaters is consistent with previous evidence suggesting an adverse impact of meat intake. The lower risk of postmenopausal breast cancer in vegetarian women may be explained by their lower BMI. It is not clear whether the other differences observed, for all cancers and for prostate cancer, reflect any causal relationships or are or due to other factors such as residual confounding or differences in cancer detection.