Gut microbiota and cancer prevention

Do you know that there is a link between cancer and the bacteria in your gut? Scientists have found out that the gut bacteria can influence the development of cancer in the body as well as how a cancer patient response to the treatment. This has been an active area of research in recent years.

What is microbiota?

Our body is a host for not only our own cells, tissues and organs, it is also home to tens of trillions of microorganisms. These are tiny living cells which are mainly bacteria, and some viruses and fungus, etc. It is estimated that there are as many bacteria cells in our body as the number of our own cells.1 These microorganisms survive and thrive on the surface of the body, mostly on the epithelium, i.e. the thin tissue that form the outer layer of the body and inner lining. Skin, gastrointestinal (GI) tract, respiratory tract, vagina, are all colonized by them. Collectively, the diverse range of microorganisms coexists and builds cooperative ecological community referred to as microbiota.1 The GI tract has an abundance of microorganisms that is termed ‘gut microbiota’.

The role of gut microbiota in human health

Microorganisms in the gastrointestinal tract

We develop our gut microbiota at birth. The mother’s womb is generally considered a sterile environment. The natural birth process of passing through the virginal starts to introduce microbiota. The GI tract is rapidly colonised with the infant’s interaction with the environment. By the age of 2.5 years old, the composition, diversity and functional capabilities of the gut microbiota of a child is fully developed and resembled those of the adults.2 No two persons have the same composition of gut microbiota and the relative abundance of different bacteria groups changes with the age.3

Vitamin B12 is generated by bacteria in the gut

Microbiota exists in symbiosis within the GI tract. The gut microbiota thrives in the warm, protected, and nutrient-rich microenvironment of the intestines. In return, it assists the body in the digestion of complex carbohydrates, produces vitamins (e.g. vitamin B12), generates non-nutrient essential factors, regulates the maturation of the immune cells, and prevents the colonisation of harmful microorganisms.4 As such, the equilibrium of gut microbiota is essential to maintain good health.

The link with cancer

An estimated 20% of cancer worldwide are caused by microbes. The most well-known example is the Helicobacter pylori bacteria that is linked to gastric cancer. Studies have shown that the overgrowing of H. pylori promotes inflammation, increases cancer proliferating signals, and disrupts the immune system ability to destroy cancer cells.5

H pylori ulcer diagram en
H. pylori is known to cause stomach ulcer and increase the risk of gastric cancer

However, H. pylori is not a pure villain. It also plays a role in modulating the level of a type of hormone call ghrelin in the body. Ghrelin, also known as the “hunger hormone”, is generated when the stomach is empty, it signals the brain to induce hunger. When the stomach is stretched with food, the production of ghrelin stops. Scientists discovered that H. pylori help to stop the production of ghrelin. By eradicating H. pylori, a person will tend to overeat and increase the risk of obesity.6 Hence, gut microbiota equilibrium is the key to health.

Eradicating H. pylori can lead to obesity.

Disequilibrium in the intimate relationship between the body and the gut microbiota is called dysbiosis. This can be caused by many factors: attack by harmful microbes, aging, antibiotics, xenobiotics, smoking, hormones, improper diet, genetic defects, etc. All these factors are also well-established risk factors for cancer development.7

Studies have shown that alteration of the composition of the gut microbiota influences the incidence and progression of colorectal cancer. This is because several by-products of the gut microbiota, such as the short-chain fatty acids, are known to be able to destroy cancer cells or suppress cancer growth. Beyond the GI tract, experimental studies have also shown alteration of gut microbiota can affect the incidence and progression of other cancer types including breast and liver.7

How to avoid dysbiosis?

To avoid dysbiosis, it is important to avoid unnecessary use of antibiotics. Antibiotics can severely reduce the population and alter the composition of gut microbiota.8 In fact, overuse of antibiotics increase the risk of cancer.9

No Smoking - American Cancer Society's Great American Smoke Out
Say no to smoking
Maintain a healthy lifestyle and diet is also important for a healthy gut microbiota. Here are the lifestyle factors that one must place attention:

  • Avoid smoking – Smoking is found to alter both the composition of the gut microbiota as well as decrease its diversity. Smoking promotes oxidative stress, changes the intestinal structures and proteins, and disrupts the acid-base balance.10
  • Maintain regular exercise – Exercise can enrich the gut microbiota diversity as well as stimulate the proliferation of bacteria which can modulate mucosal immunity and improve barrier functions.11
  • Manage stress – The gut-brain axis is modulated by the gut microbiota. Dysbiosis has been implicated in a variety of stress-related conditions including anxiety, depression and irritable bowel syndrome.12
  • Keep a healthy weight – Weight gain is linked to certain bacteria and the two has a reciprocal relationship. 13
  • Avoid frequent travel – Frequent travel affects gut microbiota in many ways including infection, diet change, pollution, etc. 14
Manage your stress – The gut-brain axis is modulated by the gut microbiota

Diet has the most direct influence on the gut microbiota. A healthy diet goes a long way to protect the balance of gut microbiota. Here are a number of dietary items that one should consider increasing the intake to promote a healthy gut microbiota: 15

Tempeh – a source of plant-based protein and probiotics
  • Plant-based protein – Plant-based protein increases good bacteria strains such as Bifidobacterium and Lactobacillus, which helps to increase the production of short-chain fatty acids.
  • Fibres – Fibres are non-digestible carbohydrates which serve as fuels, or pre-biotics, to the gut microbiota.
  • Probiotics – Supplementing with good bacteria from fermented food such as kefir, yogurt, miso, etc.
  • Polyphenols – These are antioxidants in fruits, seeds, vegetables, tea, cocoa products. They can enrich bacterial genera in the gut.
Plant-based diet – this is what your body and your bacteria in the gut need most


A healthy and thriving gut microbiota can protect us from cancer. Dis-equilibrium of gut microbiota can lead to increase inflammation, reduce immunity, and promote cancer cells growth. Hence, it is important to avoid unnecessary use of antibiotics, maintain a healthy lifestyle, and eat the right food to maintain the bacteria equilibrium in our gut to prevent cancer.


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  9. Kilkkinen A, Rissanen H, Klaukka T, et al. Antibiotic use predicts an increased risk of cancer. Int J Cancer. 2008;123(9):2152-2155. doi:10.1002/ijc.23622.
  10. Savin Z, Kivity S, Yonath H, Yehuda S. Smoking and the intestinal microbiome. Arch Microbiol. 2018;0(0):1-8. doi:10.1007/s00203-018-1506-2.
  11. Monda V, Villano I, Messina A, et al. Exercise Modifies the Gut Microbiota with Positive Health Effects. 2017;2017. doi:10.1155/2017/3831972.
  12. Foster JA, Rinaman L, Cryan JF. Neurobiology of Stress Stress & the gut-brain axis : Regulation by the microbiome. Neurobiol Stress. 2017;7:124-136. doi:10.1016/j.ynstr.2017.03.001.
  13. John GK, Mullin GE. The Gut Microbiome and Obesity. Curr Oncol Rep. 2016. doi:10.1007/s11912-016-0528-7.
  14. Riddle MS, Connor BA. The Traveling Microbiome. Curr Infect Dis Rep. 2016;18(9). doi:10.1007/s11908-016-0536-7.
  15. Singh RK, Chang HW, Yan D, et al. Influence of diet on the gut microbiome and implications for human health. J Transl Med. 2017;15(1):1-17. doi:10.1186/s12967-017-1175-y.

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