Colorectal cancer is one of the most common cancers. A growing number of studies have shown that gut bacteria have a significant impact on the development of colorectal cancer. So how do we cultivate a good gut microbiome to prevent colorectal cancer?
Bacteria in the Gut Are Closely Related to Colorectal Cancer
Colorectal cancer is affected by various risk factors, including genetic and environmental factors. However, where the genetic factor only accounts for 12 to 35 percent, the impact of environmental factors is greater. In particular, the impact of Western diet and lifestyles on the gut microbiome can increase the risk of colorectal cancer. Additionally, oral hygiene habits are also associated with the risk of colorectal cancer.
The gut microbiome of patients with colorectal cancer is different from that of healthy patients. One study found that stool and tumor samples from patients with colorectal cancer tended to have more Escherichia coli, Bacteroides fragilis, Streptococcus gallolyticus, Enterococcus faecalis, Fusobacterium nucleatum, and Porphyromonas.
Among them is Escherichia coli, a diverse group of bacteria that people often recognize. Most of these bacteria are harmless to humans, but some are still pathogenic. The American Journal of Clinical Investigation pointed out that Escherichia coli is positively associated with colorectal cancer, with an approximately 60 percent detection rate in colorectal cancer patients and approximately 20 percent in healthy individuals.
In addition, many bacteria in the feces of patients with colorectal cancer are also related to oral commensal bacteria, such as Fusobacterium nucleatum and Porrinomonas gingivalis. A large-scale study showed that women with low tooth count and moderate to severe periodontal disease had a 48 percent increased risk of colorectal cancer.
Ying-Chieh Tsai, an expert in probiotics in Asia and a chair professor at National Yang Ming Chiao Tung University, pointed out that all these studies used comparative methods to compare the differences in the gut microbiome between healthy people and patients with colorectal cancer, and found these differences. However, the scientific community still does not understand exactly how these bacteria affect colorectal cancer.
The current most accepted theory is that these “bad” bacteria disrupt the balance of the gut microbiome and release toxins that affect cell regulation or directly damage cells. They also produce toxic metabolites, cause chronic inflammation, and change intestinal permeability. These changes affect the mucosal cells of the large intestine; cumulative damage can lead to abnormal cell proliferation and genotoxicity, resulting in adenomas and even colon cancer.
The Butyrate Paradox: Promotes Gut Health but Causes Cancer?
Another factor in the association between gut bacteria and colorectal cancer is the secretion of the bacterial metabolite butyrate by these bacteria, which can induce cell aging and inflammation, and promote tumorigenesis.
Paradoxically, however, short-chain fatty acids produced by gut bacteria fermenting dietary fiber, especially butyrate, have been found to balance the gut microbiota, maintain the mucosal barrier, modulate the host immune response, prevent infection, and regulate energy expenditure. Therefore, butyrate-producing bacteria are considered probiotics.
Tsai emphasized that every kind of bacteria will produce butyrate to some extent; bad bacteria will also produce them but in a small amount, and the harm of bad bacteria mainly comes from the toxins they produce. The paradoxical effects of butyrate have indeed been discussed over the years, and this is known as the butyrate paradox.
There are several views and findings on this topic:
Concentration of butyrate
The appropriate concentration of butyrate is beneficial to the human body, but it is harmful when it is too high; the problem is that the true cutoff value is not yet known.
Stem cells
Stem cells can renew and differentiate; they can proliferate into the same type of cells, and can also differentiate into cells with other functions.
The growth of intestinal cells is derived from the differentiation of stem cells. Butyrate inhibits stem cell growth, but it promotes the growth of normal cells that differentiate from stem cells. Then, the normal cells will in turn protect the stem cells from butyrate.
Tsai says that we still do not understand the reason behind it, but “the growth of stem cells is not necessarily good, as it may lead to the differentiation and growth of cancer cells.”
The state of gut health
Butyrate is harmful if the intestinal tract is in a state of severe ulceration. On the other hand, it is beneficial for people with mild intestinal ulcers or those who are completely healthy. This view has been widely accepted in recent years.
So is butyrate good or bad? Tsai believes that the good outweighs the bad; however, the intake of fiber should be reduced when the intestinal tract is severely inflamed and ulcerated. For the same reason, people with poor gut health or who have just undergone surgery should not take probiotics, as fiber and probiotics will increase the level of butyrate.
He reiterated that patients with colorectal cancer need to pay attention to the timing of taking probiotics. Such patients are more likely to have an imbalance of gut microbiota, and they need to take probiotics. It is not recommended that patients take probiotics right after surgery or during chemotherapy. Instead, they can take the supplements after the acute phase passes.
3 Ways to Regulate Gut Microbiome to Prevent Colorectal Cancer
Does reducing specific bad bacteria in the body lower the risk of colorectal cancer? Yuan-Yu Jeng, a former chief physician at the Department of Infectious Disease of Taipei Veterans General Hospital, pointed out that the microbiota of the digestive tract are in a state of dynamic balance with the human body, and various microorganisms in the internal environment form a complex ecosystem. Trying to get rid of certain bad bacteria from the body will not necessarily lead to a good outcome, as the whole system is affected.
It is also not a good idea to prevent certain types of bacteria from entering the body, mainly because most of these bacteria are part of the body’s natural system. Some bad bacteria already exist in the body, and they will still overgrow in an imbalanced environment.
Jeng says that the fundamental solution is to maintain the micro-ecosystem in the body, which includes maintaining a healthy diet, exercise, good mental health, regular sleep schedule, oral hygiene, and controlling chronic diseases such as the “three highs.”
Nonetheless, modulating the gut microbiome is still a powerful tool in colorectal cancer prevention. There are several specific methods to do this:
1. Change your dietary habits
Improving the gut microbiome takes time. One way to do this is by increasing the consumption of fermented foods (such as yogurt), as well as implementing a moderate intake of fiber-rich vegetables, fruits, and grains.
Several studies have shown that excessive intake of red meat and processed meat may increase the risk of developing colorectal cancer. When the diet residues entering the colon are mainly protein residues and bile acids secreted by the liver to digest fat, they may cause damage to colonic cells through proinflammatory and proneoplastic effects after being fermented by intestinal bacteria, leading to an increased risk of colorectal cancer.
A Mediterranean diet consisting mainly of fruits and vegetables, high-quality fats, and high-quality protein can reduce the incidence of colorectal cancer. One of the reasons is that the Mediterranean diet can increase the good bacteria in the gut and cultivate a healthy gut microbiome.
Tsai added that it may take up to half a year for people who have a poor gut microbiome to feel the improvement after switching to a Mediterranean diet. In addition, it is not recommended for this group of people to consume a large amount of high-fiber food at once. He explained that such people have fewer bacteria that can decompose fiber in their intestines, and a sudden intake of excessive fiber will cause discomfort. It is recommended for them to take probiotics first to directly improve the gut microbiome; after some time, they will notice the effect of dietary improvement.
2. Take a probiotic supplement
The degree of inflammation in the gut is related to the overall state of the gut microbiome. At present, there is no single bacteria strain that can improve the overall gut microbiome. Various types of bacteria need to be supplemented at the same time, such as Lactobacilli and Bifidobacteria. Tsai suggests that we choose probiotics products that contain five to six types of good bacteria.
3. Maintain oral health and good food hygiene
Good food hygiene can prevent bacteria such as E. coli from “entering the mouth and causing illness.” Oral health is also an important part of human health in general. For example, it is difficult to suppress Porphyromonas gingivalis by relying on good intestinal bacteria alone; it is also necessary to maintain oral hygiene.
Dr. Chih-Chung, an attending physician at the Center Union Dental Clinic in Taiwan, believes that effective oral cleaning reduces the number of bacteria in the mouth, which can indirectly lower the bacteria in the body and may reduce the risk of colorectal cancer.
The Bass brushing technique is currently recognized as the most effective way to brush your teeth. When brushing, hold the toothbrush bristles at a 45-degree angle to your teeth. This angle allows the bristles to gently brush the gingival sulcus, the point where the teeth and gums meet, thereby preventing the accumulation of bacteria.
Chih-Chung suggested that we carry dental floss with us, and use it to clean the triangular gap between teeth after meals. In addition, it is recommended to perform a full-mouth debridement and dental check-up every six months for better oral health.
Camille Su is a health reporter covering disease, nutrition, and investigative topics. Have a tip? kuanmi.su@epochtimes.com
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