The science shows that a healthy diet lowers cancer risk and enhances treatment. But adhering to these directives can be tricky unless you understand the mechanism. And it appears that the mechanism is once more directly related to the gut microbiome. I found that understanding the mechanism that controls and regulates the immune systems is crucial to adhering to and maintaining good dietary habits and a supplement regime during treatment.
This post is Part 3 of a 3-part deep dive into the role of diet in cancer prevention and treatment.
- Part 3 (this one) looks at the role of diet and the gut microbiome in cancer prevention and treatment
The diet microbiome cancer relationship – the science
The Gut Microbiome (GM) plays a crucial role in human physiology and the development of chronic diseases, including cancer. This is because of the GM’s ability to stimulate immunity to regulate inflammatory, metabolic, and infectious diseases. The microbiota’s influence on cancer development depends on chronic inflammation or direct effects on immune cells. A diet that nurtures a healthy gut microbiota is critical to human health.
A study published in the Journal of Translational Medicine found that the western diet, which is high in animal protein and saturated fatty acids and low in fibre, leads to a decrease in beneficial bacteria and an increase in unhealthy bacteria. People consuming polyunsaturated fats possess good bacteria in their gut.
In contrast, those consuming high carbohydrates are colonised predominantly by harmful bacteria. The microbiota of obese people has limited diversity in their gut microbiome. On the other hand, plant-based diets, including the MD and vegan diet, are rich in fermentable nutrients that promote a microbial flora rich in healthy species.1
Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5859494/
In the figure above, the left part shows the main interaction mechanisms between a healthy diet, a healthy and diverse GM and the immune system. The right part of the figure shows alterations in the immune system and intestines due to an unhealthy diet and unbalanced gut microbiota.
GM diversity also plays a crucial role in the immune system. The human genome cannot encode all the information needed to guarantee health. Molecules secreted by the intestinal microbiome overcomes deficiency. The interaction between microbes and the immune system is bidirectional.
The study concluded that there was a significant opportunity to develop new drugs and combine probiotic supplements with vaccines and cancer immunotherapies.
How diet impacts the gut microbiome and increases cancer risk
A study published in the National Library of Medicine examined how cancer development is associated with the microbiome. Direct pathways include the colonisation of pathogens in the gut. Indirect pathways include bacterial production of carcinogens from external sources such as diet.2
Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4121395/
The Gut Microbiome and Colorectal cancer
Although my cancer initially manifested in my bladder, it later spread to my colon. When I received my metastatic bladder cancer diagnosis, the lining of my colon had mutated. Subsequent changes to my diet, the addition of supplementation and treatment have reversed these changes.
A 2021 study published in the Frontiers of Nutrition found a significant association between the gut microbiome and colorectal cancer (CRC). The review aimed to update evidence on how diet can benefit the gut microbial composition. The study highlighted the importance of a plant-based diet and supplements in cancer prevention by improving the gut microbiome.
Dietary factors play an essential role in the vitality of the gut microbiome that regulates the inner lining of the colon and rectum. The composition of the GM is a decisive factor in cancers such as colorectal. An unhealthy GM is associated with impaired immune response and the release of carcinogenic substances, essential mechanisms implicated in CRC risk.
Diets low in dietary fibres and high in red meat predispose individuals to CRC. A healthy GM supported by dietary fibre and phytonutrients decreases cell proliferation by regulating genetic changes. Emerging evidence shows that the predominance of harmful bacteria can predispose the colon lining to cancer. Dietary and lifestyle modifications block the growth of harmful bacteria. A combination of prebiotics, postbiotics and probiotics can protect the intestinal lining by improving immune response and decreasing the production of toxic substances, oxidative stress and cell proliferation.
The study concluded that dietary constituents such as fibre, polyunsaturated fatty acids found in oily fish (DHA and EPA), prebiotics, probiotics, and postbiotics might lower the risk of colorectal cancer. Beneficial strains of bacteria protect the inner lining of the colon and rectum against inflammation and cancer development.4
Diet the microbiome and cancer immunotherapy
A review published in the MDPI journal examined the relationship between Diet, Microbiome, and Cancer Immunotherapy. The immune system plays a crucial role in cancer suppression. The review found that plant-based dietary patterns favourably altered the gut microbiome’s composition.
A well-tuned GM supports the immune system’s anti-cancer response. Data shows that gut microbiota strongly influences the response to cancer immunotherapy, chemotherapy, and radiotherapy.
Specific bacteria species inhabiting the GM can have a beneficial influence on immunotherapy. Factors like vitamins, glucose, or BMI may also change the cancer treatment response. The review demonstrated a strong association between diet, gut microbiome composition, and the outcome of immunotherapy.4
The Mediterranean Diet, in particular, is associated with beneficial changes in gut microbiota and increases the total amount of bacteria inside the gut.
The review examined the following dietary patterns concerning the gut microbiome and cancer-fighting properties.
Paleo
The Paleo diet mimics humans of the Stone Age. It consists of fruit, herbs, spices, and vegetables. Meat, fish, and egg consumption is medium to high. It excludes processed foods. The study found that the diversity of the GM was comparable to Hadza hunter-gatherers.
However, recent scientific evidence implicates the Paleo diet with undesirable side effects. Findings from a 2019 study show that long-term adherence to a Paleolithic diet changes the gut microbiota composition and increases serum TMAO levels associated with poor cardiovascular health. The anomaly may be due to the lack of resistant starch.
Fasting
Fasting is a diet pattern in which a person restrains themselves from consuming solid food for a certain period. Every other day of fasting leads to increased levels of good bacteria inside the gut. Different forms of fasting, such as intermittent fasting, multiday fasting, and diets mimicking fasting, improve the intestinal microbiome diversity.
Carbohydrates and artificial sweeteners
Excessive intake of refined sugars increases bile output, which triggers the proliferation of harmful bacteria. High sugar consumption leads to smaller diversity of species in gut microbiota. Replacing carbohydrates with resistant starch in mice with pancreatic cancer modified their gut microbiota by shifting the balance towards the anti-inflammatory species. It reduced the intestinal levels of harmful bacteria while promoting the growth of good bacteria. Artificial sweeteners induce detrimental changes in the intestinal flora. Saccharin-fed mice had a less diverse gut and more harmful bacteria.
Ketogenic diet
The ketogenic diet is a low-carbohydrate diet that produces ketone bodies. This diet aims to mimic a fasting state by making fat instead of carbohydrate a dominant caloric source. Data suggests that a ketogenic diet can reverse dysbiosis associated with neurological disorders.
Gluten-free diet
A gluten-free diet is a diet that excludes all sources of gluten. It has been shown to lower the number of harmful bacteria and does not affect beneficial species. The beneficial properties of the gluten-free diet come from the reduction of fructans.
Low-FODMAP diet
A low-FODMAP diet is a diet considered to be beneficial to patients with inflammatory bowel syndrome (IBS). Subjects following a high-FODMAP diet had decreased good bacteria and GM diversity levels. The long-term use of the FODMAP diet is problematic due to the limited amount of healthy plant foods and natural probiotics.
Intermittent fasting and the microbiome
Intermittent fasting (IF) has gained popularity in recent times thanks to the popularity of Dr Micahel Mosley’s television shows. Advocates for IF claim that it can help you lose weight, increase energy, improve mental clarity, and live longer.
Intermittent fasting alternates between periods of eating and abstinence from food. One popular method is the 16:8 protocol, where you eat all your meals within an 8-hour window (for example, 10 am to 6 pm) and fast the rest of the day. This is the fasting method I follow.
Another approach popularised by Mosley is the 5:2 method. You restrict your caloric intake for two days of the week and eat a regular, healthy diet for the other five days. I’ve tried this protocol in the past but found it too tricky to adhere to over time. Then there’s alternate-day fasting, where you fast every other day. Intermittent fasting studies in mice show increased microbial diversity, reduced inflammation, and increased production of short-chain fatty acids.
While certain types of fasting help with weight loss, it is unclear how the gut microbiome is involved. One study found that individuals who followed the 16:8 pattern had higher microbial richness than those who followed their usual eating patterns. Some studies have found that individuals had increased levels of beneficial gut bacteria after Ramadan. Fasting also increases diversity and levels of the beneficial butyrates, which are all associated with a healthy gut microbiome.5
It also turns out your gut microbiome has its own circadian clock. Sleep plays an essential role in cancer prevention and treatment, so it is worth understanding how this works. Studies show that the composition and function of the microbiome fluctuate throughout the day. It turns out that short-chain fatty acids from fibre digestion play a role in the liver’s expression of ‘circadian clock’ genes. The liver plays an essential role in regulating sleep. Certain things can disrupt this rhythm, including high-fat diets and jetlag. Intermittent fasting can restore circadian rhythm patterns.
Conclusion
There is no doubt that the gut microbiome plays a crucial role both in cancer treatment and prevention. Understanding the mechanism that links diet to cancer through the gut microbiome has helped me adhere to a healthy diet during my recovery. It also further underlines the vital role that the microbiome plays in cancer prevention and treatment in relation to diet and exercise, and sleep.
References
- The influence of diet on anti-cancer immune responsiveness; Available from URL: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5859494/
- Gut Microbes, Diet, and Cancer; Available at URL: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4121395/
- Emerging Evidence on the Effects of Dietary Factors on the Gut Microbiome in Colorectal Cancer; Available at URL: https://www.frontiersin.org/articles/10.3389/fnut.2021.718389/full
- Diet, Microbiome, and Cancer Immunotherapy—A Comprehensive Review; Available at URL: https://www.mdpi.com/2072-6643/13/7/2217
- What science says about intermittent fasting and the gut microbiome; Available at URL: https://insight.microba.com/blog/what-science-says-about-intermittent-fasting-and-the-gut-microbiome/
