The Power of Functional Foods in Cancer Prevention

We’ve all been touched by cancer in some way, whether we’ve dealt with our diagnosis or that of a family member, friend, or coworker. Cancer is the second leading cause of death in the U.S., and cases continue to rise. In 2021, over 1.6 million people received a new cancer diagnosis, and this number is estimated to grow to almost 2.3 million by the year 2050. Thankfully, we’ve gotten better at early detection and treatment, so cancer death rates have declined. Nevertheless, cancer is still a dreaded, costly diagnosis that takes a significant mental and physical toll.

While a small percentage of cancer cases have a significant genetic component, the vast majority are a result of modifiable risk factors like diet, lifestyle, and environmental exposure. Research has confirmed that what we eat has a significant impact on our overall health, and there may be certain foods that specifically reduce cancer risk. Investigations into functional foods in cancer prevention provide promising results for actionable ways to avoid a cancer diagnosis. In this article, we’ll discuss functional foods and how to incorporate them into your meal plan to reduce your cancer risk as you age.

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What Are Functional Foods? 

Functional foods are “food or beverage that imparts a physiological benefit that enhances overall health, helps prevent or treat a disease/condition, or improves physical or mental performance via an added functional ingredient, processing modification, or biotechnology.” In other words, functional foods aren’t just the sum of the nutrients they contain; their bioactive compounds impart added protection. Understanding how functional foods can play a role in cancer prevention, knowing what cancer is and how it develops, is helpful.

When you hear the word cancer, you may think of an outside invader, but cancer results when your immune system can’t keep up with your rogue body cells. Normally, your body creates new cells as they’re needed, and these cells grow and divide in an orderly process. When they get old, damaged, and aren't functioning well, your body removes these cells to prevent them from causing harm. When this process is interrupted, reactive oxygen species and inflammation-causing free radicals can damage DNA, proteins, and lipids, allowing impaired cells to grow and multiply unchecked. These damaged cells can then stick together to form cancerous or benign tumors.

Functional foods may provide anti-cancer benefits by targeting the underlying causes of cellular and DNA damage, like inflammation and oxidation. Some anti-cancer properties of functional foods include:

• Scavenging for and limiting the production of free radicals
• Protecting the body from oxidation
• Lowering inflammation
• Modulating immune system function
• Improving the gut microbial environment
• Protecting against DNA damage
• Improving gut mucosal health
• Reducing the exposure of the gut lining to toxins
• Inhibiting pathogen growth

While functional foods hold promise, it’s important to remember that cancer development is unique to an individual person. It’s unlikely that one specific available food can prevent cancer, but these foods can be an excellent addition to a tailored, comprehensive cancer prevention plan. 

Mechanisms of Cancer Prevention Through Diet 

To understand how diet can be used as a cancer prevention tool, we must discuss how food contributes to cancer development. While it would be almost impossible to say that a particular food or diet causes cancer, we do know that specific dietary patterns contribute to the underlying causes of cancer.

The standard American diet promotes obesity and inflammation (two critical cancer risk factors), possibly via its impact on the gut microbiome and the physical gut barrier. Most (70-80%) of immune system cells live in the small intestine. When gut health is compromised, the immune system has a more difficult time ridding the body of damaged cells that could become cancerous in the future.

Ultra-processed foods, which make up a large percentage of the American diet, lead to dysbiosis in the gut and changes in metabolic function. Interestingly, gut bacteria can change their metabolism quickly based on the dietary substrate they’re provided. When ultra-processed foods are consumed at a high rate, microbes may increase the amounts of virulence factors they produce, thus increasing inflammation. In addition, ultra-processed food consumption can potentially lead to a permanent loss of valuable gut bacteria. Since gut microbes are intimately involved in immune system responses, this loss may lead to changes in the epigenome that increase the risk of inflammatory diseases like cancer.  

Part of the consequence of diet-related gut microbiome changes is damage to the protective physical gut barrier in the small intestine. This single-cell barrier filters out what your body should absorb and what it should excrete. Shifting the gut microbiome toward dysbiosis leads to a leaky gut (disrupting the small intestine barrier). When barrier function is compromised, undigested food particles, pathogens, and toxins can cross into the systemic circulation, triggering an altered immune system response and inflammation, which are underlying cancer contributors.

When considering dietary mechanisms in cancer prevention, we must eat in such a way as to reduce inflammation, maintain great gut and metabolic health, and normalize immune system function. You can do this by ensuring your dietary pattern includes optimal amounts of all nutrients, especially fiber, which may reduce gastrointestinal and breast cancer risk. There’s also a role for phytochemicals in cancer risk reduction.

Phytochemicals, or phytonutrients, are chemical compounds unique to plants that provide health benefits to humans. You’ve likely heard of various phytonutrients, like polyphenols, resveratrol, and flavonoids, but many others exist. Phytonutrients are functional foods that provide antioxidant, anti-inflammatory, and anti-cancer benefits. They also modulate the immune system and promote optimal gut health. 

Essential Functional Foods for Cancer Prevention 

There are several categories of functional foods in cancer prevention. While no single food on its own will prevent cancer, there are many evidence-based cancer-preventive foods to consider adding to an overall anti-inflammatory meal plan.  

Carotenoids

This group of over 50 plant and animal compounds is essential for photosynthesis, development, and propagation. Regarding cancer prevention, various carotenoids scavenge and limit the production of free radicals, protect against oxidation, modulate immune system function, and reduce inflammation.

• Astaxanthin, found in green algae, salmon, and trout, crosses the blood-brain barrier to target free radicals in the brain. 
• Lycopene, found in tomatoes, tomato products, watermelon, grapefruit, apricots, pink guava, and paw, prevents the production of inflammatory mediators like interleukin-8 (IL-8). In one study of men with prostate cancer, when compared to people who ate five servings of fruits and vegetables per day, those who consumed 30 grams of lycopene per day experienced slowed growth of prostate cancer and 47% higher lycopene concentration in prostate tissue. 
• Lutein, found in green leafy vegetables, bell peppers, grapes, sweet corn, peas, egg yolk, kiwi fruit, and zucchini, may reduce the risk of breast, lung, and colon cancers. Beta-cryptoxanthin, found in human milk, whole wheat products, oranges, orange juice, peaches, papayas, mangos, watermelon, nectarines, plums, grapefruit, black olives, red bell peppers, and tangerines, may reduce the risk of breast, cervical, and lung cancers.
• Beta-carotene, found in green leafy vegetables, oranges, and yellow fruits and vegetables, may protect against breast cancer.
• Curcumin found in the spice turmeric acts as an antioxidant and anti-inflammatory agent for cancer prevention, and it’s currently being studied as a treatment for various cancers.  

Isothiocyanates

Isothiocyanates are derived from the breakdown of sulfur-containing compounds in cruciferous vegetables called glucosinolates. People who eat the highest amounts of broccoli, broccoli sprouts, cauliflower, kale, Brussels sprouts, and cabbage tend to have lower cancer rates overall. Several studies have linked this group of functional foods and their metabolites to lower lung, breast, liver, esophageal, stomach, small intestine, and colon cancer risk. Unfortunately, standard cooking methods can reduce the biological activity of these compounds, so eating them raw may be the best way to obtain maximum cancer-preventive effects.

Probiotics and Probiotics

Probiotics are live bacteria that benefit humans when consumed in adequate amounts. Prebiotics are the fibrous parts of plant foods that humans can’t digest but feed bacteria. Probiotic food sources include yogurt, natto, kimchi, kefir, sauerkraut, and fermented vegetables. Prebiotic food sources include legumes (beans and lentils), oats, green bananas, cooked and cooled potatoes, asparagus, dandelion greens, onions, leeks, and apples.

Probiotics help to ensure the health and function of the gut microbiome and the gut lining by maintaining normal barrier function, inhibiting pathogen growth, and supporting diversity. Probiotics also act to modulate the immune system. Prebiotics provide energy to colon cells, keep the gut barrier, improve immune system function, and lower inflammation. Probiotics have been found to protect against DNA damage in the colon, and a combination of pre-and probiotics (synbiotics) may reduce colorectal cancer risk. 

Phytoestrogens

Phytoestrogens, including isoflavones, lignans, coumestans, and flavonoids, are found in a wide variety of plant-based foods like berries, pomegranate, soybeans, olives, grapes, apples, cocoa, green tea, and coffee. They act similarly to the hormone estrogen, can protect DNA from oxidation and damage, and provide an anti-inflammatory benefit. 

As a group, phytoestrogens have been found to cause cancer cell death preferentially, and people who consume the most soy isoflavones (genistein and daidzein) have lower cancer rates. One meta-analysis found high soy intake to decrease breast cancer risk in both pre-and post-menopausal women. While some claim phytoestrogens like soy may be problematic for women recovering from breast cancer and men, the vast majority of research does not support this. High-quality research has found phytoestrogens like soy may reduce prostate, endometrial, thyroid, skin, and colorectal cancer risk. 

When employing functional foods against cancer, it’s best to consistently include a variety of foods from all of these groups rather than focusing on any one group or food. 

Integrating Functional Foods into Daily Diet

Unfortunately, there are no single foods that will keep you safe from cancer. Instead, the dietary pattern, on the whole, matters most in the long run. Consistently eating to maintain optimal gut health and prevent chronic inflammation and oxidation can go a long way in the battle to keep you safe from cancer. 

There are a variety of dietary strategies for cancer prevention. If you’re new to making nutritional changes, the Mediterranean diet is a great place to start. This dietary pattern has been studied extensively and has been found to keep inflammation and blood sugar in check and promote gut microbiome diversity. A systematic review and meta-analysis found those who follow the Mediterranean diet closely tend to have a lower risk of cancer overall. 

The Mediterranean diet includes many functional foods like antioxidant-rich fruits, vegetables, and herbs, legumes and beans, minimally-processed whole grains, and healthy fats. Red meat, eggs, and dairy are kept to a minimum, and ultra-processed foods and sugar are discouraged. 

Once you lay the foundation with a wholesome, anti-inflammatory meal plan, you may want to incorporate specific functional foods into your diet as a part of your overall plan for cancer prevention. While there are many available food supplements, it’s always best to rely on whole-food sources first and only supplement if needed. Here are some tips for adding more functional foods to your daily diet:

• Add raw collard greens, yogurt, uncooked oats, and a green banana to a berry smoothie in soy milk for breakfast.
• Have a loaded salad topped with walnuts, olives, and orange slices for lunch.
• Enjoy iced or hot green tea.
• Have apple slices with almond butter for a snack
• Serve a lentil burger and raw Brussels sprouts salad for dinner.

Beyond food, the Mediterranean diet encourages physical activity, social interaction, and stress management practices, all of which foster an anti-cancer environment in the body.

Functional Foods and Personalized Nutrition 

Personalized nutrition refers to using unique information about a person, like genetic single nucleotide polymorphisms (SNPs), to tailor nutritional recommendations. Research is underway to determine how specific genetic SNPs may impact nutrient absorption and function in the body and, thus, disease risk. While still in its infancy, this research may help providers better customize nutrition recommendations to provide benefits above and beyond what someone could attain with a one-size-fits-all approach. Let’s take vitamin D as an example. This hormone is vital for proper immune system function and, thus, cancer prevention. Some people have SNPs that impact vitamin D binding protein, affecting how they absorb vitamin D from the sun, supplements, and food sources. Identifying this SNP in an individual patient may help providers better tailor vitamin D recommendations as one tactic in a comprehensive cancer prevention strategy. 

But beyond genetics, all humans have different lifestyles and preferences and other environmental exposures and risk factors. Considering these variables is likely far more critical than genetic SNPs in most cancer cases and offers a way to optimize the cancer-preventive benefits of functional foods. Common cancer risk factors include age, alcohol and tobacco use, chronic inflammation, diet, hormones, infections, obesity, sunlight and radiation exposure, and immunosuppression. Fortunately, the majority of these can be mitigated with diet and lifestyle. Personalized nutrition for cancer prevention means taking a step back and viewing an individual patient holistically. Tailoring diet for cancer risk reduction requires practitioners to assess and address health status, genetics, and risk factors in a specific individual and to customize their plan in such a way as to support their unique needs. 

Challenges and Considerations 

Cancer results from multiple factors, some of which have more of an effect than others, so it may be challenging to know where to start on your journey. Of course, balancing diet in cancer prevention is crucial, but so is sleeping well, managing your stress level, moving your body, and feeling connected to others. These general strategies create the foundation you need to prevent a cancer diagnosis. However, they take a significant personal commitment, and misinformation abounds, especially regarding nutrition. To add another layer, there may be challenges in using functional foods. For example, if you have an overgrowth of bacteria in your small intestine, hammering it with prebiotic and other fibrous foods can lead to significant gastrointestinal symptoms, inflammation, and a dysregulated immune system response, all things we want to avoid when trying to prevent cancer. You may need to take a step back and work with a knowledgeable provider to heal your gut first and then add in these types of functional foods. 

Additionally, there are a myriad of persuasively marketed supplements and foods that make it difficult to know what’s helpful for cancer prevention and what may be a waste of your time and money or even harmful. As one example, highly bioavailable turmeric, which may be cancer-preventive, could also lead to liver injury in some people. Working with a savvy healthcare provider can help you wade through the massive amount of information that’s out there, as well as your health data, to prioritize the most critical factors and distill the evidence into actionable steps for you.

The Future of Functional Foods in Cancer Care

Much research has shown a significant connection between diet and all types of chronic, inflammatory diseases, including cancer. Advancements in cancer nutrition research have suggested a link between functional foods and reduced cancer risk. Billions of dollars are spent on cancer research every year, and we’ve gotten pretty good at effectively treating many of the most common cancers like breast and prostate. However, our traditional healthcare system focuses on treating rather than preventing illness. The truth is a large percentage of cancer cases may be completely avoidable with personalized diet and lifestyle strategies. In the future, more randomized controlled trials studying the effect of diet and lifestyle on cancer development are needed. And it’s vitally important to change the messaging around cancer to empower individuals to take proactive measures, like adding functional foods to their diet, to prevent a cancer diagnosis. 

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Functional Foods For Cancer Prevention: Final Thoughts

Cancer results from the interplay between genetics and factors like diet, lifestyle, and environmental exposures. While cancer may seem inevitable, there’s a lot you can do to significantly reduce your cancer risk. Functional foods can be part of a personalized nutrition plan to lower inflammation, maintain great gut and metabolic health, and optimize immune system function. But nutrition is just one aspect of a comprehensive cancer prevention plan. Partnering with an integrative and functional healthcare provider can help you prioritize additional lifestyle strategies to give you the best chance of avoiding a cancer diagnosis.