Gut Health: The link between gut bacteria and cancer risk and response

Gut bacteria: The key to health

All disease begins in the gut. ~ Hippocrates

We have 70 trillion cells in our body. And we have 100 trillion cells in our gut. Meaning the gut bacteria we house far outnumber our own cells. There’s a reason we evolved to house these commensal organisms: they are there to keep us healthy and prevent disease. This includes cancer.

Researchers are finding that our gut flora impacts not just the obvious food and digestion-related issues such as weight gain and cravings, but conditions as diverse as our sleep and our mental health. Why is that? An estimated 70-80% of our immunity resides in the gut.

Gut Health and Immunity

Our digestive system is the main route of contact with the external environment. Every day it is overloaded with external substances, sometimes dangerous. Pathogens (bacteria, protozoa, fungi, viruses) and toxic substances enter our systems along with food or commensal flora. When you think of it this way, it makes perfect sense that the integrity of our digestive system (our gut) is essential to our health.

Basically, we want to make sure our gut health is in optimal condition to fight off invaders like the flu and other unsavory microbes that may enter our system. But it’s not just the foreign substances the immune system must handle: it responds to anything that causes inflammation in the gut and keeps our gut flora in proper balance.

If anything disrupts this fine balance, causes inflammation, or goes unrecognized or unchecked by the immune system, then we’re in trouble. We get sick, or worse, chronic disease can get a foothold.

Gut Health: The Science

Researchers are now focusing on the role of gut health in cancer risk, and more specifically how our unique composition of gut flora predicts risk. Furthermore, they are looking at how manipulation of gut flora composition may control cancer progression and predict response to treatment.

Birth, feeding and our gut flora

As it turns out, our earliest moments on earth have a significant and direct impact on our gut flora, and therefore on our immunity. Compared with babies born ‘naturally,’ babies born via caesarean section have been reported to have lower numbers of good bacteria and higher numbers of bad bacteria in their gut flora composition.

Research to further understand this relationship is ongoing, but current understanding holds that infants who were born via caesarean section do indeed have different gut bacteria and are more likely to develop allergies and immune-related diseases like asthma.

Similar patterns have been found in formula-fed infants versus those who were breastfed. The findings suggest that early diet and exposure to a variety of environments and bacteria through diet shapes our gut microbiota from are earliest days, therefore impacting our immunity.

Antibiotics and the gut

Antibiotic use has also been on the rise over the past several decades, and they are highly effective against those bad bacteria that can cause illness.

Unfortunately for us and for our overall health, these nonspecific drugs wipe out the good bacteria as well as the bad guys, leaving the gut susceptible to hostile takeover by foreign invaders – aka the bad bacteria.

So how does this all relate to cancer risk?

Gut flora control our immune system, and our immune system controls gut flora. Researchers are finding that this interaction is key in determining cancer risk. A study on mice found that those lacking anti-inflammatory cytokines, molecules that slow the immune response, have more bad bacteria in their gut. What does this mean? A strong immune response safeguards our guts from an overpopulation of bad bacteria.

Furthermore, they found an increased risk of colorectal cancer in these mice. They have even conferred risk to other mice by taking the feces of the donor mouse lacking the cytokines and feeding it to a recipient with balanced gut flora. The bad bacteria flourished and took over the microbiota of the recipient. In turn, the recipient’s risk of colorectal cancer increases.

Similarly, a study on humans found an increased risk of colorectal cancer in relation to long-term antibiotic use. As I alluded to above, antibiotics disrupt the balance of gut flora.

Chemotherapy, Immunotherapy, and Gut Flora

Another study has found that cancer treatment therapies are less effective in germ-free mice, which have been bred in completely sterile conditions. They have no bacteria – good or bad. Certain immunotherapy and chemotherapy drugs are activated by the immune system itself. What this study found is that the gut flora itself modulated this activation: the lack of microbiota resulted in reduced efficacy of the treatment drugs.

A different study was conducted on mice with tumors that were treated with cyclophosphamide – a common chemotherapy drug used in many cancers (it was part of my own chemo cocktail). The study found that healthy gut flora promoted an adaptive anti-tumor immune response.

Again, the germ-free mice and those who had received antibiotics to kill these specific bacteria were resistant to the drug and tumor shrinkage was diminished. When they transferred more of these healthy cells to these mice, the anti-tumor efficacy of the chemo was partially restored.

Once again, we have evidence that the interaction of gut flora and the immune system is a crucial factor in treatment response.

Enzyme activation and microbiota modulators

Treatment efficacy also relates to liver enzymes. Many chemotherapy drugs are activated by these enzymes as well as by the gut bacteria. Different levels of liver enzymes impacts how effective the chemo will be. Germ-free mice have more enzymes that detoxify the chemotherapy, which may sound like a good thing. But if the chemo leaves the system too quickly, it has less time to do its tumor-fighting job.

Gut bacteria modulate this response. Once researchers transferred the bacteria to the germ-free mice, treatment response improved dramatically. Yet, high levels of bad bacteria can over-activate the chemotherapy drugs, which can cause worsened side effects as the drugs kill both the good cells as well as the bad.

One of the more unpleasant and more dangerous side effects of chemotherapy is diarrhea. It starves patients of vital nutrients, dehydrates the system, and can change the microbiota of the gut. Evidence from human studies suggest that bacteria levels do in fact predict whether a patient will suffer from this side effect.

The Upshot: Let food be thy medicine.

So what does this all mean for cancer patients and people aiming to prevent cancer? We need healthy guts! Diet is key, and high-quality probiotics are essential. Check out this video with cute animated bacteria for a primer on gut bacteria.

Dietary fiber is the optimal fuel for the good gut bacteria, so a diet high in fruits, vegetables, nuts and seeds is optimal for promoting gut health. The more fiber-rich foods you ingest, the more good bacteria colonize the gut, restoring the balance. Raw, slightly steamed and lightly cooked produce retain the most benefits.

Fermented foods like sauerkraut actually contain these helpful bacteria, so consuming both fresh and fermented is key.

What else helps improve diversity of gut flora? Coffee, tea, red wine, and, yes, dark chocolate! These foods, along with fruits and vegetables, are rich in polyphenols, which are anti-oxidants.

Here are the top foods rich in probiotics, in ranked from excellent to good:

• Sauerkraut
• Kimchi
• Pickles
• Kefir*
• Yogurt*
• Buttermilk*
• Raw Cheese*
• Tempeh**
• Natto**
• Kombucha

As for your best bets – sauerkraut, kimchi, pickles, and kombucha – look for unpasteurized versions with little to no added sugar (kombucha varies – opt for lower sugar).

**Please note: tempeh and natto are soy products, and while these unprocessed fermented forms are better than other soy products, too much soy in any form can have a negative impact on health, as they are usually GMO and contain estrogen, so should absolutely be avoided for breast cancer patients.

*Please note: Kefir, yogurt, buttermilk, and raw cheese are dairy products, and dairy can cause inflammation is not recommended for cancer patients. Yogurt often contains a lot of sugar, and sometimes lacks live cultures.

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