This article was written by one of The Food Medic team; registered dietitian – Maeve Hanan.
April is Bowel Cancer Awareness month and so we are shining a light on some of the associated dietary risks.
A number of factors impact bowel cancer risk, including medical history, genetics and age. But lifestyle factors, like diet, also play a role. This article will explore the current evidence-based findings related to diet and bowel cancer risk.
Note: This article uses the terms ‘colorectal cancer’ rather than ‘bowel cancer’ to be more specific, as colorectal cancer refers to cancer that starts in the colon or retum in the large intestine. Whereas ‘bowel’ refers more generally to the small intestine, colon, rectum or anus.
A 2017 report from the World Cancer Research Fund (WCRF) concluded that consuming foods containing dietary fibre “probably protects against colorectal cancer” (1).
This is likely to be related to the effect of fibre in the bowel. For example, fibre helps with the bulk of stools and the movement of stools through the gut which reduces exposure of harmful compounds in the stools on the gut lining. Fermentation of fibre in the gut also leads to the production of short chain fatty acids, like butyrate, that have been seen to have a protective effect on the cells in the bowel (2).
High-fibre foods like fruit and vegetables also contain compounds linked with cancer prevention, like antioxidants and phytoestrogens (2).
Wholegrains are linked with a probable reduced risk of colorectal cancer (1). Infact, a 17% lower risk of colorectal cancer has been identified for those who consume 90g of whole grains per day; this is roughly 3 servings of wholegrains per day (1).
Although the evidence is less robust, there is also a possible link between consuming a low intake of fruit and non-starchy vegetables and a higher risk of colorectal cancer (1). This would make sense considering that fruit and vegetables are a great source of fibre, antioxidants, vitamins and minerals.
Fruit and vegetables tend to contain vitamin C, and foods containing vitamin C may also be linked with a reduced risk due to the antioxidant and DNA-protective effect of vitamin C, but overall evidence for this is limited (1).
Consuming dairy products, milk, cheese and calcium-containing foods is linked with a probable reduced risk of colorectal cancer; however the evidence related to cheese was weaker than the others (1).
Although the mechanisms aren’t entirely clear, it’s thought that calcium can protect cells in the gut by influencing cell signalling pathways and binding to compounds that may promote cancer cell growth like free fatty acids and certain bile acids (1, 3).
Other compounds found in certain types of dairy, like vitamin D and lactic acid producing bacteria, may also play a beneficial role (4).
There is limited evidence that consuming fish may be linked with a reduced risk of colorectal cancer risk (1). More specifically, an 11% reduced risk was found per 100g of fish per day.
This may be related to the omega-3 content of fish (especially oily fish like salmon, mackerla, herring, kippers, sardines and trout), and how this impacts inflammation in the body.
Red & processed meat
The International Agency for Research on Cancer (IARC) and the WCRF classify processed meat as a cause of colorectal cancer, and red meat as a ‘probable’ cause of colorectal cancer (1, 5).
This may be due to chemicals that can be found naturally or added to meat such as:
- Haem: a red pigment found naturally in red meat.
- Heterocyclic amines and polycyclic amines: these form when meat is cooked at high temperatures, especially when it is charred or burnt.
- Nitrates and nitrites – these are added to processed meat like ham and bacon as part of the curing process.
It’s important to remember that red meat provides important nutrients so it doesn’t need to be entirely avoided, and the risks outlined above are related to regularly consuming a high intake of red and processed meat.
The WCRF recommends limiting meat intake to around three portions per week (350 – 500g cooked weight), and having little to no processed meat (6). The UK government recommends that those who consume more than 90g (cooked weight) of red and processed meat per day should reduce this to 70g per day (7).
There’s a significant link between alcohol consumption and colorectal cancer risk, as well as a number of other types of cancer including head, neck, throat, liver and breast cancer (8).
In fact roughly 6% of bowel cancers in the UK may be related to drinking alcohol (9).
Based on a review of the evidence, the WCRF concluded that drinking two or more alcoholic drinks per day increases the risk of colorectal cancer (1).
Taking calcium supplements (200 – 1000mg per day) is linked with a likely reduced risk of colorectal cancer (1). As discussed above, there are a number of possible reasons as to why calcium might be protective but ongoing research is needed.
There’s also a possible link between vitamin D, both from food and supplements, and reduced colorectal cancer risk, which may be related to the impact of vitamin D on cell growth, immunity and inflammation (10). But there’s less evidence to back this up as compared with calcium supplements (1).
There’s also some limited evidence that multivitamins might decrease the risk of colorectal cancer, possibly due to an antioxidant effect (1). However, more evidence is needed related to this, especially as there’s a lot of variety between different types of multivitamin supplements.
But it’s important to be aware that supplements can do more harm than good for our health, especially when these include very high doses of fat-soluble vitamins like vitamin A and E (11, 12). Mineral supplements, including calcium, can also reduce the absorption of other minerals. An excessive calcium supplement intake could possibly increase heart disease risk by contributing to hardening of the arteries, but evidence is mixed on this topic (13).
Looking at dietary patterns rather than individual food, nutrients or supplements can give us a more realistic view of how our diet impacts health outcomes, as we don’t consume single foods or nutrients in isolation.
A meta-analysis from 2017 found that a ‘healthy’ diet (that was high in fruit, vegetables, olive oil, wholegrains, fish, poultry, soy and dairy) was significantly linked with a lower risk of colorectal cancer compared with a Western-style diet (14).
Another study from the same year, found that diets high intake of fruit, vegetables, wholegrains, nuts, legumes, seafood and dairy products was associated with lower a lower risk of colorectal cancer when compared to those consuming more red and processed meat, sugary drinks, refined grains, potatoes and desserts (15).
A more recent study found that diets containing more anti-inflammatory foods (like fruit, vegetables, olive oil, oily fish etc.) were protective against colorectal cancer, particularly in men (16).
Consuming a good intake of fibre, fruit, vegetables, whole grains, dairy, and fish is associated with a lower risk of colorectal cancer.
Whereas, a higher intake of alcohol red and processed meat is linked with an increased risk.
This dietary pattern is also linked with overall health benefits, including for our heart and metabolic health.
Supplements may play a role, especially calcium supplements, but there are also risks related to supplements so always speak with your dietitian, pharmacist or doctor if you are considering starting a new supplement.
- World Cancer Research Fund (WCRF, revised 2018) “Diet, Nutrition, Physical Activity and Colorectal Cancer” [accessed March 2022 via: https://www.wcrf.org/wp-content/uploads/2021/02/Colorectal-cancer-report.pdf]
- Slavin, J. L. (2000). Mechanisms for the impact of whole grain foods on cancer risk. Journal of the American College of Nutrition, 19(sup3), 300S-307S. [accessed March 2022 via: https://pubmed.ncbi.nlm.nih.gov/10875601/]
- NIH Website “Calcium and Cancer Prevention” [accessed March 2022 via: https://www.cancer.gov/about-cancer/causes-prevention/risk/diet/calcium-fact-sheet]
- Norat, T., & Riboli, E. (2003). Dairy products and colorectal cancer. A review of possible mechanisms and epidemiological evidence. european Journal of clinical nutrition, 57(1), 1-17. [accessed March 2022 via: https://pubmed.ncbi.nlm.nih.gov/12548291/]
- WHO (2015) “IARC Monographs evaluate consumption of red meat and processed meat” [accessed March 2022 via: https://www.iarc.fr/wp-content/uploads/2018/07/pr240_E.pdf]
- WCRF Website “Limit red and processed meat” [accessed March 2022 via: https://www.wcrf.org/dietandcancer/limit-red-and-processed-meat/]
- NHS Website “Meat in Your Diet” [accessed March 2022 via: https://www.nhs.uk/live-well/eat-well/meat-nutrition/]
- NIH Website “Alcohol and Cancer Risk” [accessed March 2022 via: https://www.cancer.gov/about-cancer/causes-prevention/risk/alcohol/alcohol-fact-sheet]
- Cancer Research UK Website “Risks and causes of bowel cancer” [accessed March 2022 via: https://www.cancerresearchuk.org/about-cancer/bowel-cancer/risks-causes]
- Dou, R., Ng, K., Giovannucci, E. L., Manson, J. E., Qian, Z. R., & Ogino, S. (2016). Vitamin D and colorectal cancer: molecular, epidemiological and clinical evidence. British Journal of Nutrition, 115(9), 1643-1660. [accessed March 2022 via: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4890569/]
- Goodman, G. E., Thornquist, M. D., Balmes, J., Cullen, M. R., Meyskens Jr, F. L., Omenn, G. S., … & Williams Jr, J. H. (2004). The Beta-Carotene and Retinol Efficacy Trial: incidence of lung cancer and cardiovascular disease mortality during 6-year follow-up after stopping β-carotene and retinol supplements. Journal of the National Cancer Institute, 96(23), 1743-1750. [accessed March 2022 via: https://pubmed.ncbi.nlm.nih.gov/15572756/]
- Alpha-Tocopherol Beta Carotene Cancer Prevention Study Group. (1994). The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. New England Journal of Medicine, 330(15), 1029-1035. [accessed March 2022 via: https://pubmed.ncbi.nlm.nih.gov/8127329/]
- Myung, Seung-Kwon, Hong-Bae Kim, Yong-Jae Lee, Yoon-Jung Choi, and Seung-Won Oh. “Calcium supplements and risk of cardiovascular disease: A meta-analysis of clinical trials.” Nutrients 13, no. 2 (2021): 368. [accessed March 2022 via: https://pubmed.ncbi.nlm.nih.gov/33530332/]
- Feng, Y. L., Shu, L., Zheng, P. F., Zhang, X. Y., Si, C. J., Yu, X. L., … & Zhang, L. (2017). Dietary patterns and colorectal cancer risk: a meta-analysis. European Journal of Cancer Prevention, 26(3), 201-211. [accessed March 2022 via: https://pubmed.ncbi.nlm.nih.gov/26945285/]
- Tabung, F. K., Brown, L. S., & Fung, T. T. (2017). Dietary patterns and colorectal cancer risk: a review of 17 years of evidence (2000–2016). Current colorectal cancer reports, 13(6), 440-454. [accessed March 2022 via: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794031/]
- Jakszyn, P., Cayssials, V., Buckland, G., Perez‐Cornago, A., Weiderpass, E., Boeing, H., … & Agudo, A. (2020). Inflammatory potential of the diet and risk of colorectal cancer in the European Prospective Investigation into Cancer and Nutrition study. International journal of cancer, 147(4), 1027-1039. [accessed March 2022 via: https://pubmed.ncbi.nlm.nih.gov/31945199/]
Diet & bowel cancer risk was last modified: March 17th, 2022 by