The old adage that you are what you eat has never been more true than for cancer. It may not be the only cause or the only treatment, but it can play a fundamental role in outcomes. There is no doubt about the role of the Western diet in cancer development and the benefits of a healthy diet like the Mediterranean Diet in preventing cancer. But the relationship between diet and treatment, such as immunotherapy, is less well known.
Being told to stop eating red meat and processed foods and start eating a healthy diet is one thing. Sticking to the plan is another. It’s not good enough to be told just what to do. You need to understand why a particular diet is good for you. By understanding the mechanism that lowers cancer risk or enhances treatment, you have a better chance of adhering to the diet.
Armed with this knowledge, you can also be more mindful of what you eat, adding to its potency.
The relationship between diet and cancer is such an important one that I have divided the subject into three parts.
- Part 1 (this one) looks at the best diet for prevention and treatment according to the science
- Part 2 looks at supplements’ role in enhancing cancer treatment effectiveness
- Part 3 looks at the role of the Microbiome in cancer prevention and its treatment
In Part 1, I focus on the MD diet’s role in enhancing the effectiveness of immunotherapy as this is the treatment and dietary pattern I am currently following.
Diet and cancer immunotherapy
One of the most exciting developments in cancer treatment has been the field of immunotherapy. The relationship between diet and immunotherapy is particularly interesting to me as I am currently undergoing a two-year immunotherapy treatment program.
Using the immune system in the fight against cancer has been around since Dr William Coley triggered an immune response in cancer patients in the late 19th Century by injecting inactivated bacteria. With the recent development of new drugs, many cancer patients benefit from immunotherapy. So far, immunotherapy has been proven effective against melanoma, kidney, lung and bladder cancer.
The immunotherapy mechanism involves the “retraining” of the immune system to identify and destroy cancer cells. By blocking specific proteins, immunotherapy drugs enable the immune system to attack and destroy cancer cells. This approach differs from standard chemotherapy, where the drug destroys cancer cells and many healthy cells.
Chemotherapy is a blunt instrument, while immunotherapy is like a sharp scalpel. Immunotherapy enables the body’s natural anti-cancer processes to be more effective. The exciting this is that you can enhance the effectiveness of immunotherapy by eating a healthy diet and taking the right supplements.
Comparing healthy dietary patterns
A recent review in the Journal of Translational Medicine examined the dietary mechanisms that influence prevent cancer and enhance the effectiveness of immunotherapy in particular. Healthy diets include dietary components that behave as antigens as part of the immune system. The study compared the functional components of a range of healthy diets, including Mediterranean, Vegetarian, Japanese, and Low Carbohydrate diets.1
Mediterranean diet
One of the more well-known cancer prevention diets is the Mediterranean dietary pattern. It is a diet rich in fresh ingredients simply prepared. Research links the MD diet with a decrease in the incidence of many chronic diseases, including cancer.
The Mediterranean diet consists primarily of fish, vegetables, legumes, grains, fruit, extra virgin olive oil, wine, and small amounts of red meat. Crucially, it limits processed foods and refined sugar. It is essentially a plant-based diet with some animal products allowed in moderation.
One study found that high adherence to a Mediterranean diet reduces cancer mortality risk. The incidence of several cancer types, including colorectum, breast, stomach, pancreas, prostate, liver, and head and neck cancers, were also reduced. A recent study from the University of Texas suggests that adhering to the Mediterranean diet can reduce the risk of prostate cancer progression to a higher grade.
Twelve primary prevention studies analysed reduced cancer mortality with an MD-style diet. A study on children who followed a Mediterranean diet compared to controls, who disregarded health food recommendations, demonstrated different immune profiles.
According to a study published in the American Journal of Clinical Nutrition, research shows that women who consume an MD diet may have a lower risk for breast cancer. A study in the Archives of Medicine showed a reduced risk of pancreatic cancer by eating a diet rich in fruit, vegetables, whole grains, fish, and healthy fats such as olive oil. In other words, eating an MD diet.2
What makes the MD diet so effective?
There is no single ingredient in the MD diet producing favourable effects. Instead, it appears to be the result of the complex food pattern characteristic of the MD. Specific aspects of the Mediterranean diet, such as high fruit and vegetable, whole grain, and low processed meat intake, are associated with lowered risk of cancer progression.3
A healthy MD is a combination of quality foods, including the absence of contaminating substances such as pesticides, fertilisers and endocrine disrupters, which can alter the intestinal microbiota. Avoiding containment damage to the intestinal microbiota is why you should always wash your fruit and vegetables. The savings from junking processed foods allows you to source fruit and vegetables from quality suppliers, including organic.
The critical factors of the MD diet that protect against cancer inflammatory responses are low cholesterol levels and high levels of antioxidants in fruits and vegetables. Consumption of monounsaturated fatty acid (MUFA) in fish, nuts and olive oil is also key.
Among MD components, olive oil has been the subject of several studies suggesting its protective role in cancer. There are associations between increased consumption of olive oil and decreased risk of developing breast and colorectal cancer. A scientific review found an inverse relationship between olive oil consumption and the prevalence of breast or digestive system cancers.
MD Diet and Nutrient Bioavailability
One of the ways that the MD diet has proven to be effective is food preparation. Some nutrients can be lost during cooking, while some nutrients become more bioavailable when cooked. Salad incorporates raw vegetables into the diet and is consumed frequently in Mediterranean countries.4
Just how the MD diet maximises, the bioavailability of ingredients is listed below.
- Extra virgin olive oil – Polyphenols, including hydroxytyrosol, from Extra Virgin Olive Oil has anti-aging and cancer-fighting effects. Most cooking with olive oil in the MD diet is done at low to medium heat, preserving its benefits. Raw olive oil is added to salads and drizzled over cooked foods such as soups, stews, fish, and vegetables. Eating unpitted olives is another method of including olive oil in the diet. The pitting process decreases hydroxytyrosol by 50%. Kalamata black olives have the highest hydroxytyrosol content, followed by Spanish-style green and Greek-style black olives.
- Tomatoes – Tomatoes are an example of a food that has improved bioavailability when processed and cooked. Cooking tomatoes in olive oil promotes the absorption of the carotenoids, including lycopene, across the intestinal wall. Carotenoids are phytonutrients that act as antioxidants to help protect your cells. The good news is that carotenoid availability is increased by canning and bottling. So you can gain all the benefits of carotenoids by using liberal amounts of passata. Or you can try my favourite snack from the island of Malta, Kunserva tomato paste liberally spread with olive oil and salted capers on fresh crunchy bread.
- Cruciferous vegetables – Cruciferous vegetables are foods that have improved the bioavailability of phytochemicals when eaten raw. However, they are rarely eaten raw in the Mediterranean. Adding raw cruciferous vegetables such as broccoli and sprouts restores up to 100% of sulforaphane formation. Sulforaphane is a proven cancer fighter. I get my fill of sulforaphane daily from broccoli sprouts and their extract when unavailable. It is worth noting that soups and stews are the most common way of consuming cruciferous vegetables in the Mediterranean. This cooking method retains the nutrients rather than losing the liquid when cooked in boiling water. Studies have shown that steaming broccoli until it turns a bright green will boost its cancer-fighting compounds.
- Alliums – Alliums contain cancer-fighting organo-sulphur compounds and flavonoids. Crushing garlic and chopping onions help release these substances. However, the enzymes are deactivated when cooked at high temperatures. The preparation should happen about 20 minutes before cooking at low temperatures. Another tip is to sprinkle small amounts of raw garlic and onions or leeks on salads.
- Nuts – Nuts are an essential part of the Mediterranean diet. They are rich in unsaturated fats, protein, fibre, minerals, folate, magnesium, and calcium. The highest concentration of antioxidants is in the skin.
The key takeouts from MD-style diets are:
- High consumption of fruit and vegetables with access to phytonutrients
- Increased consumption of legumes and beans for gut health
- Consumption of fish for access to Omega 3
- Consumption of olive oil, tomatoes and nuts
- Low consumption of red meat and dairy foods
- High adherence rate due to a variety of food groups allowed
Vegetarian diet
The vegetarian diet includes dietary patterns that have a common basis, including the abstinence of meat and fish. A vegetarian-style diet rich in antioxidants and fibres should decrease cancer incidence and mortality. However, scientific evidence about the anti-cancer effect of vegetarianism remains scarce compared with the data available for MD.
Surprisingly, a review of nine studies including breast, colorectal and prostate cancer did not find any anti-cancer association between a vegetarian and a non-vegetarian diet. Instead, the study found an association between a lower risk for colorectal cancer and a semi-vegetarian diet. The study defined a semi-vegetarian diet as eating meat more than once per month but less than once per week. A pescetarian diet, described as fish consumption more than once per month, was also beneficial.
The study found that strict vegans, who exclude all animal products, including eggs, dairy and honey, risk deficiencies in vitamin B12, zinc, iron and n-3 polyunsaturated fatty acids. Vitamin D deficiency through the lack of fish and seafood consumption is also possible. The study recommended that supplements of these elements are necessary to avoid serious health problems in vegetarian-style diets.
The key takeouts from vegetarian-style diets are:
- High consumption of fruit and vegetables with access to phytonutrients
- Increased consumption of legumes and beans for gut health
- No consumption of red meat, and no dairy in the case of Vegans
- May require supplements to overcome dietary restrictions
- Can be challenging to adhere to due to dietary restrictions in social situations
Japanese diet
Japan leads the world in overall life expectancy. The JD is a low-calorie diet rich in foods that promote the immune system’s ability to fight cancer. A key characteristic of the Japanese diet is the consumption of green tea, rich in flavonoids, which have anti-cancer properties. High consumption of vegetables, and among them miso soup, containing seaweed also has anti-cancer activity. The primary source of proteins is fish, especially salmon and tuna fish. Oily fish are rich sources of Omega 3 oils that block the growth of colorectal, breast, and prostate cancer cells. Another common protein source is the high intake of tofu, which has proven anti-cancer properties.
The key takeouts from the Japanese diet are:
- Low calorific consumption
- Green tea high in flavonoids
- Consumption of oily fish, including Omega 3
- Low consumption of red meats and dairy foods
- High consumption of tofu
Low calorie and Ketogenic diets
The results for low-calorie and ketogenic diets are less clear. Studies have demonstrated the positive effects of very-low-carbohydrate ketogenic diets (VLCKD) on different diseases. Some findings suggested that VLCKD could delay cancer progression. High glucose blood levels can increase cancer risk since glucose is the energy source for human cell proliferation, including cancerous cells.
Since carbohydrates are well-known to increase glucose and insulin, a diet composed of fat and protein could play a role in treating cancer patients. Fasting cycles retarding the growth of tumours and sensitising a range of cancer cell types could enhance chemotherapy.
The key takeouts from the low calorie and ketogenic diets are:
- Low caloric intake associated with anti-cancer benefits
- Fasting may benefit chemotherapy patients
- Difficult to adhere to a highly restrictive diet long term
- Difficult to adhere to for patients who are already experiencing weight loss
- Restricting carbs, including fibre-rich legumes and beans, may have an impact on the GM
Intermittent Fasting and Cancer
The final piece of the dietary puzzle for me is intermittent fasting.
Substantial evidence demonstrates that obesity increases the risk and worsens the prognosis of many cancers. Weight management is crucial to patients with cancer and cancer survivors. Intermittent fasting is an established form of weight reduction. As obesity is a leading risk factor for cancer, it makes sense that IF is also an effective method of cancer risk reduction.
However, recent research also shows how intermittent fasting can support cancer treatment.
Research published in 2021 in the journal of Cancer Discovery suggested that intermittent fasting may boost the effectiveness of cancer treatments. The analysis showed that levels of cancer-fighting immune cells were higher after the fast-mimicking diet. Changes also indicated that the immune system recognised cancer as something it should attack.5
Studies indicate the beneficial effects of fasting for cancer patients include:
- decreased blood glucose production
- stem cells triggered to regenerate the immune system
- balanced nutritional intake
- increased production of tumour-killing cells
In a 2016 study, research showed that a combination of fasting and chemotherapy slowed the progression of breast cancer and skin cancer. The same showed fasting makes cancer cells sensitive to chemotherapy while protecting normal cells.6
Another study published in the Cancer Journal For Clinicians found that combining immunotherapy, chemotherapy, and fasting improved tumour responses. It also suggested that prolonged fasting in cancer patients is safe and can decrease chemotherapy-related toxicity and tumour growth.7
Vegetarian vs the MD Diet
A contentious question is whether strict vegetarian diets are better than non-vegetarian diets like the MD diet for cancer prevention and treatment. There are lots of contradictory studies, and I have tried them both. A recent study published in BMC Medicine journal looked at precisely this question. The study assessed the associations of vegetarian and non-vegetarian diets with cancer risk.
The study found that being a low meat-eater, fish-eater, or vegetarian was associated with a lower risk of all cancer. Low meat-eaters had a reduced risk of colorectal cancer. Vegetarian women had a reduced risk of breast cancer. Men who were vegetarians or pescatarians had a lower risk of prostate cancer.
In addition to excluding meat, vegetarians consume more plant foods such as fruits, vegetables, and whole grains. Evidence from the European Prospective Investigation into Cancer and Nutrition-Oxford and the Adventist Health Study-2 shows that vegetarians may have a reduced risk of cancer overall compared to meat-eaters.
But the evidence remains unclear for individual cancer types. The cancer risk in those who do not consume meat but eat fish may differ from that of meat-eaters. Some evidence suggests that fish-eaters may have a lower overall risk of cancer and a lower risk of colorectal cancer. But no differences have been reported in breast or prostate cancer risk.
Any difference in cancer risk between diet groups may be due to differences in physiological characteristics. Vegetarians and fish-eaters have lower body mass indices than the body mass index (BMI). BMI an important for cancer risk because obesity is a known risk factor for several cancer types.
Another explanation for the lower risk of cancer observed amongst vegetarians and fish-eaters is the possible differences in hormone levels such as insulin-like growth factor and testosterone. A plant-based diet, whether MD or Vegetarian, is associated with more healthy and diverse GM.8
A study published in MDPI also looked at the impact of plant-based dietary patterns on cancer-related outcomes. It was explicitly comparing Vegetarian diets to the Mediterranean diet. The review concluded that there is limited evidence regarding the beneficial effects of vegetarian diets on preventing cancer-related outcomes. The study concluded that there is evidence regarding the association between the MD pattern and cancer mortality.9
Compared with the Mediterranean diet, the vegan diet is more restrictive. It focuses on foods to avoid rather than which foods to eat. Veganism is also associated with an elevated risk of nutritional deficiencies. The MD diet encourages enjoying a variety of nutrient-dense ingredients like healthy fats, fibre-rich fruits and vegetables, whole grains, and small amounts of healthy meat, including fish.
This variety in the MD diet makes it easier to adhere to. The MD diet can also contribute to overall wellness by sharing appetising meals with family or friends. I’ve found the vegan diet can be socially restrictive and difficult to sustain within a family environment. A restrictive diet can cause stress which is not helpful for any health outcome. Let’s also not underestimate food’s role in giving us pleasure and sensory delight as a part of our well-being.
On the other hand, people may also choose a vegan diet due to ethical or environmental concerns rather than just for personal health. It is quite common to feel that meat is repugnant after a cancer diagnosis or during chemotherapy. I certainly have experienced this. There are times when a strict vegan diet has made sense to me. For now, a diet based on the MD diet works best for me.
Adapting the best cancer prevention and treatment diet for you
Based on science, there is no black and white answer regarding the best diet for cancer prevention and treatment other than avoiding the standard Western diet. Instead, we should see diet as a continuum, something we adapt to our current circumstances at a point in time.
What I like about the MD diet is that it is less restrictive than other diets, including low-carb and vegetarian-style diets. It is more social and enjoyable, and adherence is less complex. One of the issues I’ve always had with restrictive diets is that it takes the joy out of eating with family and friends. While a more restricted diet might have marginal health benefits over a more flexible diet, the stress they cause may negate any advantage.
I’ve also adapted the MD diet to fit my circumstance and personal preferences. I’ve added elements from other healthy dietary patterns. I drink green tea and consume tofu and seaweed from the Japanese diet. I periodically restrict calories through intermittent fasting to maximize therapeutic benefits. I don’t drink wine, but I take Resveratrol as a supplement.
Finally, you need to be wary of advice to eat high fat, high protein diet and sugary food to maintain weight during treatment. You can still maintain weight by eating plenty of good fats, fruit, vegetables, and legumes. Such a diet will keep your weight on, strengthen gut health and optimise your response to treatment. Eating a high-calorie Western-style diet might win the battle against weight loss, but you may lose the war against cancer.
References
- The influence of diet on anti-cancer immune responsiveness; Available at URL: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5859494/
- Mediterranean Diet May Lower Cancer Risk; Available at URL: https://news.cancerconnect.com/survivorship/mediterranean-diet-may-lower-cancer-risk
- Cancer and Mediterranean Diet: A Review; Available at URL: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6770822/
- Mediterranean Diet for Cancer Prevention; Available at URL: https://www.naturalmedicinejournal.com/journal/mediterranean-diet-cancer-prevention
- Fasting-Mimicking Diet Is Safe and Reshapes Metabolism and Antitumor Immunity in Patients with Cancer; Available at URL: https://aacrjournals.org/cancerdiscovery/article/12/1/90/675618/Fasting-Mimicking-Diet-Is-Safe-and-Reshapes
- Fasting and Cancer; Available at URL: https://www.healthline.com/health/fasting-and-cancer
- Intermittent fasting in the prevention and treatment of cancer; Available at URL: https://acsjournals.onlinelibrary.wiley.com/doi/10.3322/caac.21694
- Risk of cancer in regular and low meat-eaters, fish-eaters, and vegetarians: a prospective analysis of UK Biobank participants; Available at URL: https://bmcmedicine.biomedcentral.com/articles/10.1186/s12916-022-02256-w
- The Impact of Plant-Based Dietary Patterns on Cancer-Related Outcomes: A Rapid Review and Meta-Analysis; Available at URL: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7400843/
