There are several main factors that can reduce your chances of getting bowel and rectal cancer. Weight optimisation, a good diet, exercise, vitamin D supplementation and regular colonoscopies.
A study co-funded by the World Cancer Research Fund, Cancer Research UK and Diabetes UK found that although being over weight was a factor in causation, that body fat position made a difference between men and women.
A higher BMI was more risky for men but for women, carrying the weight on the abdomen compared to the hips was worse. Only a 5 point increase in BMI for men increased bowel cancer by 23% in men but only 9% in women.
Higher fish and fish oil intake was associated with a 7% lower risk of bowel cancer in a European study.
Consuming flavinoid rich foods such as apples, tea and pears reduces both cancer and cardiovascular disease mortality particularly in those who also smoke and drink a lot of alcohol in a Danish study. The effects levelled off at around 500mg a day for all cause and cardiovascular mortality and 1000mg a day for cancer related mortality.
If you are unfortunate and get colorectal cancer, an Edinburgh analysis of seven RCTs has found that Vitamin D supplementation produced a 30% reduction in adverse outcomes.
Vaughan-Shaw et al. The effect of vitamin D supplementation on survival in patients with colorectal cancer: systematic review and meta-analysis of randomised controlled trials. Br J Cancer 2020 Sep 15.