The Science Behind Fiber and It’s Protective Role Against Colorectal Cancer.

Cover Image: BRITISH NUTRITION FOUNDATION. Fibre - Nutrition Information - British Nutrition Foundation [Internet]. British Nutrition Foundation. 2023. Available from: https://www.nutrition.org.uk/nutritional-information/fibre/

What is Fiber?

‌Dietary fiber is a type of plant-based carbohydrate that the human body cannot digest or absorb. Fiber is an important component of a healthy diet. It helps prevent constipation, lower cholesterol, manage blood sugar and reduce the risk of non-communicable diseases such as heart disease and stroke. It also has a protective effect against colorectal cancer (CRC), which is the focus of this article (1).

What is Colorectal Cancer?

Colorectal cancer (CRC) is the third most common cancer and second leading cause of cancer-related death worldwide (2). According to the World Health Organisation, in 2020, 1.9 million new cases of CRC were reported and 930,000 people died of CRC globally (3). We are also seeing an increase in CRC diagnoses in those under 50 years of age (4).

CRC starts in the colon or the rectum. These cancers can also be called colon cancer or rectal cancer, depending on where they start. The colon and the rectum make up the large intestine, which is part of the digestive system. Colon and rectal cancer are often grouped together as they have features in common (5).

Fiber and Colorectal Cancer

Scientists have concluded that there is a significant association between a higher total dietary fiber intake and a reduced CRC risk (1).

There are two forms of fiber – soluble and insoluble fiber. Soluble fiber dissolves in water, forming a gel-like substance. It feeds the good bacteria in the large intestine, producing beneficial short-chain fatty acids. Short-chain fatty acids help promote healthy gut cells, maintaining the intestinal barrier, reducing inflammation and producing protective metabolites such as butyrate (7).

Soluble fiber can be found in out bran, barley, lentils, peas and some fruit and vegetables (7).

Insoluble fiber does not dissolve, instead it holds onto water in the large intestine (8). Insoluble fire adds bulk to stool and promotes gut motility. This reduces the time in which the stool is in the large intestine, shortening the time carcinogenic agents are in contact with the bowel wall (9).

Insoluble fiber is found in wheat bran, wholegrains, nuts and seeds (8).

Other risk factors for CRC include obesity, physical inactivity, alcohol consumption and smoking (1).

How Much Fiber Should I Get a Day?

Adults should aim to have 30g of fiber a day (11). The average adult in North America consumes 17g of fiber a day (10). This raises sightly in European countries with the average fiber intake ranging from 18-24g a day (10).

Adults should aim to have 30g of fiber a day (11). The average adult in North America consumes 17g of fiber a day (10). This raises sightly in European countries with the average fibrer intake ranging from 18-24g a day (10).

• Those aged 2-5 years old would need need about 15g of fiber a day.

• Those aged 4-11 years old would need about 20g fiber a day.

• Those aged 11-16 years old would need about 25g of fiber a day (11).

Tips To Get More Fiber In Your Diet

1. Choose a higher-fiber breakfast cereal such as weetabix/shredded wheat or porridge.

2. Choose wholemeal or granary breads, wholewheat pasta, bulgar wheat and brown rice.

3. Keep your skins on your potatoes.

4. Add beans, lentils or chickpeas to stews, curries and salads.

5. Make sure you get your 5 a day!

6. For snacks, try fresh fruit, vegetables sticks, rye crackers, oatcakes and unsalted nuts/seeds (11).

References

1. Annie Y, Tao L, Chen G, Kong L. The Association of Dietary Fiber Intake with Colorectal Cancer and Related Risks: A Literature Review of Recent Research. Journal of Agriculture and Food Research. 2025 May 1;101999–9.

2. Bray F, Laversanne M, Sung H, Ferlay J, Siegel RL, Soerjomataram I, et al. Global Cancer Statistics 2022: GLOBOCAN Estimates of Incidence and Mortality Worldwide for 36 Cancers in 185 Countries. CA: A Cancer Journal for Clinicians [Internet]. 2024 Apr 4;74(3):229–63. Available from: https://acsjournals.onlinelibrary.wiley.com/doi/10.3322/caac.21834

3. World Health Organization. Colorectal Cancer [Internet]. World Health Organization. 2023. Available from: https://www.who.int/news-room/fact-sheets/detail/colorectal-cancer

4. Patel S, Murphy C, Lieu C, Hampel H. Chapter One - Early Age Onset Colorectal Cancer. In: Berger F, editor. Advances in Cancer Research [Internet]. Academic Press; 2021 [cited 2026 Jul 4]. p. 1–37. Available from: https://doi.org/10.1016/bs.acr.2021.03.001

5. American Cancer Society. What Is Colorectal Cancer? [Internet]. www.cancer.org. American Cancer Society; 2024. Available from: https://www.cancer.org/cancer/types/colon-rectal-cancer/about/what-is-colorectal-cancer.html

6. Jia M, Chen J, Liu X, Xie M, Nie S, Chen Y, et al. Structural characteristics and functional properties of soluble dietary fiber from defatted rice bran obtained through Trichoderma viride fermentation. Food Hydrocolloids. 2019 Sep;94:468–74.

7. Williams BA, Mikkelsen D, Flanagan BM, Gidley MJ. “Dietary fibre”: moving beyond the “soluble/insoluble” classification for monogastric nutrition, with an emphasis on humans and pigs. Journal of Animal Science and Biotechnology. 2019 May 24;10(1).

8. He Y, Wang B, Wen L, Wang F, Yu H, Chen D, et al. Effects of dietary fiber on human health. Food Science and Human Wellness. 2022 Jan;11(1):1–10.

9. Bars-Cortina D, Martínez-Bardají A, Macià A, Motilva MJ, Piñol-Felis C. Consumption evaluation of one apple flesh a day in the initial phases prior to adenoma/adenocarcinoma in an azoxymethane rat colon carcinogenesis model. The Journal of Nutritional Biochemistry. 2020 Sep;83:108418.

10. McKeown NM, Fahey GC, Slavin J, van. Fibre intake for optimal health: how can healthcare professionals support people to reach dietary recommendations? BMJ: British Medical Journal [Internet]. 2022;378:1–8. Available from: https://www.jstor.org/stable/27416319

11. NHS. How to get more fibre into your diet [Internet]. NHS. 2022. Available from: https://www.nhs.uk/live-well/eat-well/digestive-health/how-to-get-more-fibre-into-your-diet/

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