For those facing cancer, an important aspect of care is nutrition. While the best treatment options can vary widely depending on the individual and their type of cancer, dietary decisions are small yet powerful actionable steps which can play an integral role in helping to optimize health outcomes. Studies suggest that your microbiome may be just as important as what you put into your body in terms of improving or managing a number of chronic conditions including cancer.
Diet has been found to be the most influential and controllable factor in shaping the gut microbiota. An unhealthy diet can lead to a decrease in the diversity and abundance of beneficial bacteria, while a healthy diet can foster a beneficial microbiome. A well-maintained microbiome can help prevent the onset and progression of cancer by reducing inflammation and providing an environment that is unsuitable for cancer cells to thrive. In recent years, research has focused on understanding how diet can influence cancer risk and promote microbiota function in a way that enhances cancer treatment.
In this blog post, we explore how diet and certain dietary components such as fibre and polyphenols can create meaningful impacts on our gut microbiome health in order to help protect against cancer.
Diet and The Gut Microbiome
Dietary interventions provide not only an economical but also accessible way to alter the composition of our gut microbiome. Research indicates that a shift can occur as quickly as 5 days after making a change in the diet. A plant-based diet has been found to be particularly effective in stabilizing the intestinal ecosystem and promoting bacterial diversity. Additionally, a predominantly plant-based diet such as a vegetarian or Mediterranean style diet can reduce inflammation, improve insulin sensitivity, and support optimal energy balance, all of which are vital in combating chronic diseases associated with low-grade inflammation.
The ketogenic diet appears to decrease the diversity of intestinal microflora while increasing beneficial bacteria and decreasing pathogenic ones. It is common for people who follow a low carbohydrate or ketogenic diet to consume a higher proportion of meat in their diet. However, the review Ketogenic Diet and Microbiota: Friends or Enemies?, recommends consuming plant proteins (rather than animal protein) as they are more beneficial for the health of the gut microbiota. In particular, plant-derived protein has been shown to increase strains of Bifidobacterium and lactobacillus, while decreasing the abundance of Firmicutes. This leads to improved host metabolism and increased production of short-chain fatty acids. On the other hand, when animal protein is consumed, counts of bile-tolerant anaerobes such as Bacteroides, Alistipes, and Bilophila tend to increase, potentially leading to negative effects on health. 
Note: Emerging research has linked consuming red or processed meat daily with a 15-20% heightened risk of developing colorectal cancer for every 100 g consumed. A diet that includes high amounts of animal protein can disrupt gut microbiota composition and reduce the production of beneficial short-chain fatty acids.
Specific Dietary Adjustments
Certain dietary factors such as dietary fibres, prebiotics & probiotics, polyphenols, fermented foods or type of protein consumed all effect our microbiome.
Balance your diet with prebiotics
Dietary fibres are a crucial part of our daily food intake. The dietary fibres found in plant foods that cannot be digested by human enzymes and instead serve as a food source for beneficial colonic microbes are known as prebiotic fibres. They selectively nourish beneficial bacteria, allowing them to produce metabolites such as short-chain fatty acids (SCFAs). SCFAs are essential for maintaining a healthy gut environment. They help to maintain the integrity of the gut lining by providing energy to cells in the colon, thereby preventing the entry of harmful pathogens into the bloodstream, as well as helping to prevent colorectal cancer.   
Prebiotic fibres are found in a wide variety of plant-based foods, such as onions, garlic, and mushrooms as well as in non-keto friendly foods such as apples, bananas, and oats. Onions are a prebiotic powerhouse, containing both soluble and insoluble fibre as well as prebiotic compounds like fructo-oligosaccharides (FOS) and inulin. These compounds promote the growth of beneficial bacteria such as Bifidobacterium and Lactobacillus, which have been associated with reduced cancer risk and improved metabolic health. Spices like turmeric, ginger and oregano also contain prebiotic compounds that can help promote the growth of beneficial bacteria in the gut.
Note: An interesting study found that individuals who consume more than 30 different plant species weekly, many of which have prebiotic properties, have the healthiest and most diverse microbiomes.
What about fibre?
The importance of adequate fibre intake has been known for many years. In 1969, Denis Burkitt developed Burkitt’s hypothesis based on his research in Uganda. In his study, he observed that middle-aged individuals in Uganda (between 40-60 years) had a significantly lower prevalence of common age-related diseases like colon cancer, diverticulitis, hernias, diabetes, atherosclerosis and varicose veins as compared to those living in high-income countries like England. Burkitt concluded that this difference in the incidence of diseases could be due to the unique lifestyle led by people in low-income countries. Burkitt linked the emergence of certain diseases to the low intake of dietary fibre in highly industrialized countries. 
When individuals consume a low-fibre diet of less than 15g/day (which is typical of an average western diet), the production of SCFAs is decreased, and the gut microbiome metabolism shifts towards using less helpful nutrient. This can lead to the production of harmful metabolites such as ammonia (which can increase mucosal permeability) and hydrogen sulfide (which is inflammatory and causes DNA damage).
The high incidence rates of colon cancer in particular can be attributed to the lack of fibre in the diet. Studies have shown that the occurrence of colon cancer in all segments of the US population, including African Americans, is quite high, at about 65 cases per 100,000 population. In contrast, colon cancer is rarely found among African communities living in rural areas (less than 5 cases per 100,000 population), where they consume traditional low-fat, low-meat, and high-fibre (around 50g/day) diets.
Many large-scale epidemiological studies have confirmed and expanded on Burkitt's hypothesis. They show that low fibre consumption is also correlated with cancers such as liver and breast cancer, as well as increasing the risk of all-cancer mortality.   Furthermore, research has demonstrated that a high daily intake of fibre (over 30 grams) can be valuable in enhancing the probability of positive response to immunotherapy treatments.
How polyphenols impact cancer prevention
Polyphenols are a group of naturally occurring compounds found in plants. They are widely found in colourful fruits and vegetables, herbs, seeds, cereals, coffee, tea, and cocoa. This group of compounds has been found to impact gut microbial balance by reducing the levels of harmful bacteria while promoting the growth of beneficial ones. For example, dietary polyphenols have been associated with reductions in pathogenic Clostridium spp. Their ability to modulate the microbiome composition and function in conjunction with their anti-inflammatory properties, means that polyphenols can help improve overall gastrointestinal health. 
Berry polyphenols have been found to have many beneficial effects on the microbiome. Various studies have demonstrated that berry polyphenols may boost the production of short-chain fatty acids in the gut, can help modulate the immune system, improve nutrient absorption, and reduce oxidative stress in our bodies. The polyphenols derived from berries have shown remarkable effects on different types of cancer as well. Studies have demonstrated their potential for combatting colorectal, breast, oesophageal, and prostate cancer, among others.
What You Can Do at Home
To optimize gut health, it's important to vary your diet by incorporating a wide range of colourful foods, especially plant-based high-fibre options.
Start by adding more fruits and vegetables to each meal. Not only are they high in fibre, but they are also packed with polyphenols.
Aim for a daily intake of at least 30g and, if possible, 50g of fibre
Challenge yourself to consume at least 30 different plant species each week, including nuts, legumes, and herbs.
Try to eliminate all processed meats and instead opt for proteins from sources like mushrooms, nuts, and legumes.
If you do consume animal meats, limit your intake and purchase high-quality options.
Try adding berries to your breakfast, leafy greens to your lunch salad, and roasted vegetables to your dinner.
Another great source of fibre and polyphenols is nuts and seeds. Try snacking on almonds, walnuts, or flaxseeds throughout the day for a nutrient boost.
A healthy and plant-based dietary approach may be a valuable therapeutic intervention for anyone looking to improve their gut health and overall wellbeing, most especially in the context of cancer prevention. By consuming a healthy diet rich in prebiotic fibres, polyphenols, and plant-based foods, we can foster a diverse and beneficial gut microbiota, potentially reducing cancer risk and enhancing cancer treatment response. Future research is needed to understand the specific mechanisms by which a healthy gut microbiota can promote cancer prevention and treatment. However, incorporating a healthy diet and fostering a healthy gut microbiota is a promising strategy to promote overall health and reduce cancer risk.
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