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Lysanne Desharnais

Food is medicine… or just misinformation? Understanding the link between diet and cancer

Updated: Oct 11

On social media, it’s not uncommon to see articles and videos claiming the existence of “anti-cancer foods” or overhearing a conversation about how “going on this diet cured my cancer.” The discourse surrounding diet, nutrition and cancer is prone to a lot of misinformation. At the same time, this is an exciting active area of research that has huge implications for personalized medicine. Sometimes, it can be challenging to distinguish the pseudoscience from the evidence-based research, particularly on a topic that is being heavily studied in research labs, while also being at the centre of anecdotal experiences and marketing tactics.

 

Nutrition and diet are related to many aspects of our physical and mental health. People choose to eat or avoid certain foods for various reasons, sometimes due to general preferences, lifestyle, and cultural values. However, oftentimes people don’t have a choice at all, due to factors such as allergies, food insecurity or pre-existing health conditions, which can lead to social inequities resulting in cancer disparities. Thus, studying the link between diet, nutrition and cancer is complex. The link between diet and cancer has been well-established in the context of obesity, which increases your risk for 13 types of cancer (1). According to the Canadian Cancer Society, nearly 20% of cancer cases can be attributed to a combination of excess body weight, poor diet (in general), physical inactivity, and alcohol consumption (2). While it’s important to consider lifestyle factors, the intricacies of how food directly affects different aspects of cancer biology and host physiology beyond the context of obesity raises important questions.

 

The idea that diet is important for cancer progression is not new. The first study showing that diet influences tumor growth in mice was published over 100 years ago (3). This is perhaps a testament to the complexities of this relationship. In addition to individuals all responding differently to diets for a myriad of reasons (from host genetics and metabolism to certain medications), understanding the link between food and cancer poses unique challenges. For example, a single type of food may contain multiple substances that increase or decrease cancer risk through different means. The effects of a certain food item or nutrient may depend on how much of it is consumed, or how it was prepared. Since most people eat a variety of foods, it can be difficult to study specific food items or diets in general in the human population.

 

Research that is being done in this area ranges from understanding how one nutrient affects a specific molecular process in a cancer cell, to clinical trials investigating diet in combination with traditional cancer treatments. As such, context is everything. For example, it is not uncommon for plant extracts and phytochemicals to accelerate or inhibit cancer growth – but only in the context of cancer cells growing in a dish. This type of research is important for understanding basic tumor biology, but it cannot yet be translated to humans. As is the case in studying any disease, our understanding of cancer biology is constantly evolving, which can sometimes result in contradictions of what was previously known. One example of this is the discussion surrounding soy and breast cancer risk. For many years, it was thought that consuming soy, which can be found in tofu, soy milk, and edamame, increases your risk for breast cancer. This is because soy products contain isoflavones which are plant estrogens and high levels of estrogen have been linked to increased breast cancer risk. However, food sources that are rich in soy don’t contain high enough levels of isoflavones to increase the risk of breast cancer. There are now studies showing that soy consumption is actually protective against breast cancer risk (4, 5), yet the fear-mongering discussion surrounding soy products is still present.

 

Refined sugar has been in the spotlight for several years when it comes to its effect on our health. A diet high in sugar can cause weight gain and obesity, which is a well-established risk factor for several types of cancer.  However, there are lots of claims regarding the notion that you can “starve” a tumor by limiting sugar intake. The basis of this is that tumor cells use glucose (a simple sugar) to fuel their high metabolic demands. It is understandable that one may think that restricting sugar intake will prevent a cancer cell from meeting its energy requirements resulting in slower growth. The high-fat, low-carbohydrate ketogenic diet has gained a lot of attention in the context of cancer, because it restricts the amount of glucose in the body. Without glucose available, fat becomes the major fuel source. This leads to a metabolic state called ketosis, which results in the production of ketone bodies that become the source of energy for your cells. While normal, healthy cells can adapt to this shift in nutrient availability, tumor cells are not able to rewire their metabolism to use ketones as an energy source. Several studies have suggested some possible benefits of a ketogenic or very low-carb diet in the context of cancer. Studies in mice have shown that a high fat, low carb diet can slow tumor growth, protect healthy cells from damage from chemotherapy or radiation, and improve how well certain anti-cancer drugs work (6-8). However, translating some of these findings to humans is not so simple. One of the biggest concerns for the ketogenic diet is that it can accelerate cancer-associated weight loss, also known as cachexia, which can outweigh any positive effects that the diet may have. In addition, it can be difficult to adhere to such a strict diet, which has unpleasant side effects even in people who don’t have cancer. It is also important to remember that carbohydrates are an important source of energy for every cell in our body, including cancer-fighting immune cells. While the ketogenic diet has the potential for anti-cancer effects, it is essential to consider the balance of nutrients that is necessary for maintaining overall health, and more research is needed in this context.

 

The notion of diet being used in combination with traditional cancer treatments (chemotherapy, immunotherapy) is currently being studied in clinical trials (NCT04631445, NCT04645680). Interestingly, two of the diets that are being investigated are the ketogenic and plant-based diets. The stark contrast between these two dietary patterns emphasizes the importance of understanding the multifaceted impact of diet on cancer and the immune system. Just like every person is unique and responds differently to food, the same applies to cancer. In the future, it is possible that patients will be “prescribed” a diet that is dependent on their cancer type, current nutritional status, and treatment plan. While the relationship between diet, nutrition and cancer is complex and continually evolving, research advancements in this area will lead to the integration of food and other lifestyle factors as a tool to both prevent cancer, improve current treatments, and support overall health.

 

Disclaimer: the information in this article is not medical advice. Talk to your doctor if you have specific questions regarding your own care.

 

References

 

1.  B. Lauby-Secretan et al., Body Fatness and Cancer--Viewpoint of the IARC Working Group. N Engl J Med 375, 794-798 (2016).

2.  A. E. Poirier et al., The current and future burden of cancer attributable to modifiable risk factors in Canada: Summary of results. Preventive Medicine 122, 140-147 (2019).

3.  P. Rous, THE INFLUENCE OF DIET ON TRANSPLANTED AND SPONTANEOUS MOUSE TUMORS. J Exp Med 20, 433-451 (1914).

4.  Y. Wei et al., Soy intake and breast cancer risk: a prospective study of 300,000 Chinese women and a dose-response meta-analysis. Eur J Epidemiol 35, 567-578 (2020).

5.   I. Boutas, A. Kontogeorgi, C. Dimitrakakis, S. N. Kalantaridou, Soy Isoflavones and Breast Cancer Risk: A Meta-analysis. In Vivo 36, 556-562 (2022).

6.  R. J. Klement, The emerging role of ketogenic diets in cancer treatment. Curr Opin Clin Nutr Metab Care 22, 129-134 (2019).

7. B. D. Hopkins et al., Suppression of insulin feedback enhances the efficacy of PI3K inhibitors. Nature 560, 499-503 (2018).

8. J. Sremanakova, A. M. Sowerbutts, S. Burden, A systematic review of the use of ketogenic diets in adult patients with cancer. J Hum Nutr Diet 31, 793-802 (2018).

 

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