When we think about breast cancer, we often focus on genetic factors, lifestyle choices, and environmental exposures. But emerging research is shedding light on a less obvious player in this complex disease: our gut microbiome. Today, we’ll explore the fascinating connection between breast cancer and the microorganisms that inhabit our bodies, and discuss practical steps to support your gut health in the fight against cancer.

What Causes Breast Cancer?

At its core, breast cancer occurs when cells in the breast tissue begin to grow uncontrollably. This uncontrolled growth can form tumors, and in some cases can metastasize, spreading into other areas of the body. 

But why are these breast cells malfunctioning to begin with? 

There are several reasons why breast cancer (or any type of cancer) develops. Some of these reasons can be prevented by making certain lifestyle changes but other reasons for cancer can be beyond our control. Factors such as age, family history, and genetic mutations, play a big role in our propensity towards chronic disease development, including cancer. This explains why some of us still get a cancer diagnosis despite practicing healthy lifestyle habits. It also explains why some people never get cancer regardless of how they treat their bodies (those folks have good genetics!).

In addition to those factors we cannot control, there are several known lifestyle factors that, when accumulated over the years, can off-balance the normal functioning of our cells and cause them to start glitching:

• Obesity or a sedentary lifestyle
• Smoking
• Exposure to toxins
• Chronic stress
• An unhealthy diet
• Chronic inflammation

Where Does the Microbiome Come In?

In addition to the lifestyle factors, above, researchers are now learning of the connection our gut bacteria plays on the development (and treatment!) of breast cancer.

Our bodies are home to trillions of microorganisms, collectively known as the microbiome. This complex ecosystem, particularly concentrated in our gut, plays a crucial role in our overall health, influencing everything from digestion to immune function. Each person has a unique microbial signature shaped by genetics, diet, lifestyle, and environment.

Recent studies suggest that specific microbial combinations, which are unique to each person, may be linked to different types of breast cancer. This highlights the potential role of gut health in cancer development. 

Biome Composition and Cancer Development

There are several different “looks” or signatures of a person’s microbiome composition that are consistently seen in those with breast cancer. These findings suggest that an imbalanced gut microbiome may contribute to cancer development depending on which unique microbial pattern a person might have:

1. Gut Barrier Dysfunction: An unhealthy microbiome can weaken the gut barrier, allowing harmful substances to enter the bloodstream and trigger inflammation. Chronic inflammation can cause damage to our DNA and lead to cancer, including breast cancer.
2. Altered Immune Response: Up to 80% of our immune cells are located within our gut! Furthermore, beneficial bacteria in our gut help train the immune system to distinguish between what is harmful and what is friendly. An imbalance of our microbiome can thus impair our immune system from distinguishing between friend and foe (including between cancerous and non-cancerous cells). When our immune system ignores a threat, cancer cells are allowed to survive and grow.
3. Hormonal Imbalances: The gut microbiome is a key player in hormone metabolism. Certain microbial imbalances can lead to the disruption of hormones, particularly estrogen. This disruption can lead to breast cancers that are influenced by estrogen. 
4. Metabolite Production: Beneficial gut bacteria produce helpful metabolites as they breakdown our food. These metabolites benefit us in many ways including fighting off cancer cells. However, the flip-side is also true: harmful gut bacteria (or bacterial overgrowth) produces pro-inflammatory metabolites that, among other things, promote cancer development.
5. Nutrient Absorption: An imbalanced microbiome can affect the absorption of essential nutrients (vitamins and minerals) that support cellular health. The resulting nutrient deficiencies put our cells at risk and defenseless against cancerous cells.
6. Detoxification Pathways: The gut microbiome is vital for detoxification. Disruptions in these pathways can lead to toxin accumulation and increased cancer risk.
7. Gut-Brain Communication: Our gut biome communicates with our brain (called the gut-brain axis). Disruptions to this two-way signaling can influence stress responses related to cancer progression.

Creating a Healthy Microbiome Composition

Given the strong connection between our gut biome and breast cancer, it is essential to prioritize our gut health. Here are some actionable steps to adopting an anti-cancer lifestyle and fostering a healthy microbiome:

• Adopt a Diverse, Anti-Inflammatory Diet: Focus on whole foods rich in nutrients, such as fruits, vegetables, healthy fats, and proteins, while minimizing processed foods. What’s a processed food? Anything with low fiber. If a food has less than 3 grams of fiber, it’s too processed! Sugar is a HUGE source of energy/food for cancer cells, so severely limiting sugar is critical as well. Aim for 7 grams or less of sugar per serving and indulge no more than once per week (and if you can, less often than that!). Here’s some great recipes to help get you started!
• Incorporate Prebiotics and Probiotics: Eat foods rich in probiotics such as plain yogurt, kefir, sauerkraut, and other fermented foods. Make sure to accompany these with prebiotics, which are the fibrous foods that fuel our gut microbes. Prebiotics include garlic, onions, artichokes, and asparagus. 
• Limit Antibiotic Use: Use antibiotics judiciously to avoid disrupting the delicate balance of gut microbes. This not only includes prescription antibiotics to fight bacterial infections but also antibacterial soaps and cleaners. It is always best to take probiotic supplements after completing any round of antibiotics.
• Prioritize Sleep and Stress Management: Aim for quality sleep and practice stress-reduction techniques like meditation or yoga. Other stress reducing strategies are learning when to say “no,” choosing your battles, and accepting the things we cannot change.
• Stay Active: Regular physical activity supports a diverse microbiome, so find enjoyable ways to stay active for at least 30 minutes per day. Joining a hiking group or having a tennis partner are great ways to exercise with others and forming accountability.
• Minimize Exposure to Toxins: Take steps to reduce exposure to environmental toxins through air and water filtration and conscious cleaning product choices. Check out the Environmental Working Group’s cleaning products database.

The Takeaway

While more research on the microbiome and breast cancer is still being done, the findings thus far underscore the importance of gut health in cancer prevention and treatment. By nurturing our microbiome, we can enhance our defenses against cancer and improve overall health. Making these lifestyle changes helps stack the deck in our favor and gives us the best chance at fighting and preventing cancer.

Thank you Heather Bates, Functional Medicine Nurse Practitioner, for providing the research and inspiration for this blog!