The Gut Microbiome: A Key Player in Health and Disease Prevention

Dr Jennifer McQuade, a physician-researcher at MD Anderson Cancer Center, recently hosted a fascinating webinar for the Anticancer Lifestyle Program on the importance of gut health. Here is a short recap of the key takeaways from the webinar.  

What is the gut microbiome and why is it important?

• Everyone’s gut microbiome is different. The microbiome consists of the trillions of organisms that live on us and in us, primarily bacteria, along with viruses and fungi. In fact, humans have 10-100X more microbial DNA than our own DNA! The largest number of these microbes are in our GI tract. 
• We have a symbiotic relationship with the microbes in our gut. They help us digest and break down food and medications; defend us from pathogenic bacteria; break down fiber (which in turn feeds the good bacteria); and perform other essential functions.
• An unhealthy microbiome has been associated with many diseases and conditions, including obesity, diabetes, inflammatory bowel disease, cancer, eczema, allergies, asthma, and even depression (gut-brain interaction).
• There is a symbiotic relationship between our microbiome and our immune system. Exposure to microbes actually helps “train” our immune system to fight pathogenic bacteria.

What determines a “healthy” microbiome?

• Most of our microbiome is determined by the things we consume every day, such as the food we eat and the medications we take. Genetics has only a very small influence.
• A plant-based diet, exercise, and the other lifestyle behaviors taught in the Anticancer Lifestyle Program are the key ways to achieve a healthy microbiome. The bacterial composition of a healthy microbiome will vary from person to person, so it’s not meaningful, in most cases, to test for particular bacteria. Lifestyle is more of an indicator. 

What is the relationship between a healthy microbiome and cancer?

• Favorable gut bacteria decrease our risk of cancer. We’ve seen this in colorectal cancer in particular. There is some data that healthy diet and exercise improve outcomes when a patient is on chemotherapy.

What is the relationship between a healthy gut microbiome and response to immunotherapy?

• One factor determining the response to immunotherapy is the gut microbiome. In an animal study, scientists transferred the feces from mice who had responded to immunotherapy, to mice that had not responded, and the non-responsive mice started responding to immunotherapy. 

Is this relevant in humans?

• Researchers found key differences in the microbiome between humans who responded to immunotherapy, and those who did not. They transferred feces from immunotherapy-responsive humans into non-responsive mice, and the mice were then able to respond to immunotherapy. Some small studies showed that when patients who did not respond to immunotherapy got fecal transplant from responsive patients, their responsiveness to immunotherapy increased 30%.
  
• The bacteria associated with a good response to immunotherapy are the ones with known key roles in fiber digestion and fermentation. Patients who were consuming adequate fiber had an improved response to immunotherapy. Animal studies confirm this finding. 
• The obvious question then becomes, if you change the human microbiome through diet, can you improve the response to immunotherapy? These studies are happening right now. 

How do we nurture a healthy gut microbiome?

• Essentially, the best diet for a healthy microbiome is the Anticancer (anti-inflammatory) plant-based diet, full of nutrients and fiber: diverse whole grains, legumes, vegetables, and fruits. 
• Fiber is considered a “prebiotic”, meaning that it nourishes the bacteria that are already in your gut. Consuming fiber does not introduce new bacteria. It just shifts the bacterial composition of our microbiome ecosystem. In one person, certain bacteria may do most of the fiber digestion; in another person, different bacteria may perform this same function. So it’s not the specific identity of the bacteria that is important; what is important is the function the bacteria serves. That is why testing specific for specific bacteria in the gut doesn’t tell you much.
• “Probiotics”, on the other hand, are actual bacteria. Studies show that people who increase the servings of probiotic foods in their diet increase the overall diversity and richness of the gut microbiome.  Examples of probiotic foods are yogurt, kefir sauerkraut, and kimchi. These all contain live bacteria. 
• Probiotic supplements are not recommended. Paradoxically, probiotic supplements have been shown to decrease bacterial diversity in the microbiome, and reduce response to immunotherapy. Even after taking a course of antibiotics, over-the-counter probiotic supplements diminished and delayed the re-establishment of a normal microbiome. Some of the supplemental bacteria competitively excluded the beneficial bacteria already present in the gut. Probiotic supplement companies include bacteria that are easiest to culture and to distribute in mass quantities. These are not necessarily the ones that are most important for gut health. 

Conclusion:

1. There is an intimate relationship between the gut microbiome and the immune system.
   
2. Diet is a key determinant of the microbiome.
   
3. The microbiome affects the risk of cancer and other diseases.
   
4. We don’t understand why some people respond to immunotherapy and others do not. Gut health may be a factor. 
   
5. We can affect the microbiome with interventions, particularly a nutrient- and fiber-rich plant-based diet.
   
6. Probiotic supplements are not recommended.

To see the entire webinar, click here.