Probiotics linked to colon cancer risk

Probiotics, these intestinal bacteria that populate our gut, play a very important role in maintaining good health. Active research in this area yields extraordinary discoveries. A recent publication in the prestigious journal Nature suggests that the type of bacteria that makes up our intestinal flora could even play a determining role in the prevention of colon cancer.

For many, the word “bacteria” is associated with “disease”. This association is justified in several cases, since some bacteria are indeed formidable enemies that can cause serious infections that threaten the lives of infected people. It is moreover the discovery of antibiotics such as penicillin, which can eliminate these pathogenic bacteria, which played a leading role in the spectacular increase in life expectancy in the last century.

However, it is wrong to think that all bacteria play harmful roles in our lives; on the contrary, some of them even have absolutely essential functions for the proper functioning of our organism, in particular at the level of the digestive tract. The approximately trillion bacteria that live in our colon are indeed essential for the breakdown of dietary fiber and the maintenance of the immune system.

The intestinal flora even influences the levels of certain cerebral neurotransmitters and could therefore modulate certain disorders such as anxiety, stress and depression! Therefore, far from being harmful microorganisms, intestinal bacteria are on the contrary essential partners for the proper functioning of the human body.

Probiotics influenced by our diet

This important role of intestinal bacteria means that any disturbance that alters the composition and activity of this microbial flora can contribute to the development of various diseases. For example, recent studies indicate that the bacteria present in the intestine of obese people are different from those of thin people and that this difference could promote the development of liver cancer by increasing the levels of deoxycholic acid, a derivative of bile that attacks DNA and causes genetic mutations.

However, the composition of the intestinal flora is not only influenced by excess fat. Thus, people who eat a lot of foods of animal origin (meat, eggs, dairy products) harbor different bacteria in their intestines from those who eat mainly fiber-rich plants. Since heavy meat eaters have a much higher risk of colon cancer than those who prefer fruits and vegetables, it is therefore likely that these bacterial differences may contribute to this increased risk of cancer.

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To examine this possibility, a team of New York researchers compared the different types of bacteria present in the stools of people affected by colon cancer and those in good health. They observed that cancer patients had a significant drop in bacteria involved in the digestion of dietary fiber, known to play a protective role against the development of colorectal cancer, while bacteria whose metabolism is known to generate inflammatory molecules (Fusobacterium and Porphyromonas) were significantly increased.

Probiotics linked to colon cancer risk

These observations suggest that the composition of the intestinal flora is closely associated with the risk of colon cancer and that the simple fact of increasing the proportion of good bacteria, while decreasing that of the bad ones, could reduce the risk of this disease. In this sense, it is interesting to note that these changes in bacteria can be achieved very quickly, simply by integrating an abundance of plants into the eating habits. It is therefore a revolutionary vision of the role of food in the prevention of chronic diseases: fruits and vegetables are not only used to promote our health, but also that of the bacteria which have the most positive effects on our health.


Yoshimoto S et al. Obesity-induced gut microbial metabolite promotes liver cancer through senescence secretome. Nature; 499: 97-101.

Ahn J et al. Human gut microbiome and risk for colorectal cancer. J Natl Cancer Inst; 105:1907-11.

David LA et al. Diet rapidly and reproducibly alters the human gut microbiome. Nature

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