Do the bacteria in your digestive tract cause cancer? Can changes in what’s called the “gut microbiome” lead to disease? We spoke to some of the leading researchers in the country, and, for right now anyway, the answer is that they’re still trying to find out.
The "microbiome" refers to the diverse colony of trillions of microorganismsmostly bacteria, viruses, and fungithat are present in our body. These microorganisms set up shop in every part of the body: in our skin, in our mouths, in our genitals, in our guts, and most of all in our colon.
Read MoreCan The Microbiome Cause Cancer?
It could, but the evidence isn’t as straightforward as, say, the link between cancer and a direct carcinogen (like cigarette smoke, for instance). That’s because the bacteria in the microbiome all play different rolesand the “microbial makeup” of your body (the balance of the different bacteria and the different roles they all play) is unique to you. RELATED: What's the Fuss About the Gut Microbiome and Cancer?Dr. Jonathan Braun, a leading pathologist and pioneering researcher in the microbiome at Cedars-Sinai, explained two ways that the microbiome could alter someone’s cancer risk. The first would be through chronic inflammationa result of prolonged “dysbiosis,” which means a problematic change to the microbiome’s delicate balance.
What Can Throw The Microbiome Out of Balance?
Importantly, the microbiome’s “balance” is different for everyone. It essentially means the makeup of bacteria that your body has recognized as “normal” since early childhood. Dr. Braun explained that the first few years of your life are the most important as far as defining what that microbial makeup looks like.
"You acquire [these microorganisms] very shortly after birth and they evolve over your first 2-4 years of life," Dr. Braun said. "And then they settle out and then that's basically your microorganisms in a distinct way for the rest of your life."
The microbial makeup you develop in those early years of life is the one your body considers normal. Your immune system wants it to stay like this.
"Your unique microorganisms form an ecosystem that is bland to your tissue," Dr. Braun said. "So they elicit minimal inflammationsort of like a low-level neighborhood policing system."
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The "low-level neighborhood policing system" that Dr. Braun described is the reaction of your body's immune system to the microorganisms. If the makeup of bacteria in your intestines is the "normal" one you developed as a kid, your immune system will patrol it casually; it won't need to take much action.
But in some caseswhen you eat or drink something funky and your microbiome is exposed to a new organism or you somehow acquire too much or too little of one type of bacteria, the "normal" state gets thrown out of whack.
"The ecosystem could shift so that the organisms there are eliciting must stronger information. Or you've lost organisms that are making products that calm down the inflammation." Dr. Braun said, adding that inflammation over time is known to contribute to cancer risk.
How Does Inflammation in My Gut Contribute to Cancer Risk?
"Inflammation, in some cases, can promote cancer or promote growth factors that help cancers spread," Dr. Braun said. One way this happens is that the immune system's "neutrophil" cells (the white stuff inside a pimple) can release too much reactive oxygen molecules into your body if they're constantly swarming the extra or unfamiliar microorganismsand in turn, that reactive oxygen can damage your cell DNA, potentially to a point where the DNA mutates and you get cancer.
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Changes to the microbial environmentand the immune system's reaction to themare associated with many diseases and conditions, not just cancer. Inflammatory bowel disease (IBS, for instance) have been linked to the microbiome.
What About the Other Way the Microbiome Could Affect Cancer Risk?
While the inflammation that results from an "out-of-balance" microbiome (a state called "dysbiosis") is one way that the microbiome can alter cancer risk, there's another way that's more direct: certain bacteria are actually known to give off enzymes that change cell DNA directly. These are called "genotoxic" bacteria, and Dr. Braun said that one example is E. Coli.
"In that case, we have some understanding why, if you have that strain of bacteria that carries those genes, they're actually causing DNA damage," Dr. Braun said. "And in that respect, they're driving the cancer processes."
Which Cancers Can Be Related to the Microbiome?
Researchers have identified potential links between the microbiome and a number of cancers (including breast cancer and cervical cancer). The link that researchers have looked at most is that of the microbiome and colorectal cancers.
Researchers have pinpointed the microbiome as a potential player colorectal cancer rateswhich have been on the rise in younger adults for the past few decades.
According to Dr. Zuri Murrell, a colorectal surgeon in Los Angeles, people with colorectal cancer have been shown to have a higher amount of certain organisms than people who are cancer-free.
"While we don't yet know whether they play a causal role in the development of colorectal cancer in humans, we do know that certain pathogenic bacteria have consistently been shown to be more abundant in colorectal cancer patients," Dr. Murrell explained. He listed several examples of these bacteria, but said that the most notable one is "fusobacterium nucleatum."
"Many of these bacterial species can cause intestinal inflammation," Dr. Murrell said, mirroring what Dr. Braun explained about the inflammation and cancer.
How Could The Microbiome Contribute to Rising Colorectal Cancer Rates Across a Whole Generation of Young Adults When Everyone’s Microbiome is Unique?
Colorectal cancer rates are on the rise in young adults. It’s estimated that, if the current trends continue, by 2030, the incidence rates for colon cancer will increase by 90 percent for people between the ages of 20 and 34.
Researchers know that there's likely no "one cause" driving the trendand that many factors are probably at play. But several major studies have singled out changes to the microbiome as one factor.
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When I asked Dr. Braun how the microbiome could possibly be playing into rising colorectal cancer rates across an entire generation of younger adults given that everyone's microbiome is unique, he pointed to changes in our collective diets over the past few decadessuch as the rise of the "western urban diet."
"There's something now that we're doing differently from a generation or two ago and it's likely that the microbiome is part of that story," Dr. Braun said. "It's likely is that the diet has changed and that the microbiome has changed with it."
According to Dr. Braun, there are a few types of organisms that have become more abundant because of a western urban dietand a few other types of organisms that have been depleted because of a western urban diet (think processed foods, added sugar, and ingredients that generally didn't exist a few generations ago). These ingredients may be promoting excess inflammation or damaging DNA across an entire generation of peopleaccordingly, raising the colorectal risk in younger adults who were exposed to these diets from a young age, unlike older generations (in which colorectal cancer rates are actually on the decline).
Right now, Dr. Braun said, researchers have identified about a dozen or so unique organisms that are more prevalent in the western urban diet and are causing changes in our microbiomes.
If I Want to Be Cautious About My Microbiome and Cancer Risk, What Should I Do?
The main thing that affects your microbiome is what you eat.
"Having a diverse diet promotes a diverse micro-community," Dr. Braun said. "And a diverse micro-community is one that favors your healthwhether it's for cancer or diabetes or obesity."
A "diverse diet," Dr. Braun explained, means a lot of different types of fruits and veggies that are each their own "ingredients." Processed foods with long lists of ingredients, on the other hand, aren't so good.
The "Mediterranean diet"which broadly means a lot of fruits and veggies and whole grainsis one example Dr. Braun gave as a diet that promotes a healthy and diverse microbiome.
You don't have to follow a particular diet like the Mediterranean diet, though; Dr. Braun said simply making sure you're eating a lot of different types of fruits and vegetables (not necessarily a boatload of each one) is a good way to maintain that diversity.
Can Probiotics Keep The Microbiome In-Balance and Stave Off Cancer?
When people think of the microbiome, one of the first things that often comes to mind is probioticsthe supplements and drinks that are often marketed as a good way to keep your microbiome populated with the "good" bacteria.
If probiotics keep the microbiome populated with the good guys, it would make sense, in theory, that they could prevent the cancer-causing effects of having an "out-of-balance" microbiome.
But according to Dr. Braun, there's no proof that probiotics actually have any sort of preventative effect when it comes to cancer. This could be because our microbiomes have thousands of species of bacteria, and most of the probiotics out there only contain combinations of five different species of bacteria.
Dr. Murrell Spoke With SurvivorNet About Whether Probiotics Can “Prevent Cancer”
"Probiotics are not equivalent to your microbiome," Dr. Braun said. "They're just five different species as opposed to thousands, so with probiotics, you're just getting 0.5 percent of the contributions that you need."
That said, Dr. Braun did add that there's no harm to taking probiotics, and those five species of bacteria are indeed "good," so people who take them regularly as part of their health approach shouldn't necessarily stopbut they shouldn't count on them to replace the important benefits of eating a diverse diet, and they shouldn't count on them to prevent cancer.
Dr. Murrell gave us a similar response when SurvivorNet asked him about whether probiotics prevent colon cancer. "Probiotics help [when] we don't get what we need from the food we have," he said. "But they're not magic."
Can Too Many Antibiotics Throw The Microbiome Out of Whack and Cause Cancer?
Because antibiotics work (as their name suggests) by eliminating bacteria, and in turn, dangerous infections, they can cause temporary changes to the microbiome. But according to Dr. Braun, the idea that antibiotics wipe out the entire microbiome is a myth. "Even if you're taking chronic antibiotics, you still have a diversity of organisms," Dr. Braun said. "And I know of no evidence that taking antibiotics over time cause a particular change in the ecosystem which is cancer-promoting."
There are some problems with long-term antibioticsand they can cause unpleasant side effectsbut there's no evidence that cancer is one of these problems. Plus, Dr. Braun pointed out the important fact that if you're taking antibiotics that a doctor prescribed to you, it means you have a problem (likely an infection) you need to get rid ofand in many cases, letting that problem go untreated can pose an immediate danger.
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