Mouth Microbiome Plays Pivotal Role in Overall Health

Our mouths are teeming with bacteria, which isn't a bad thing—if eat certain foods and foster the most helpful bacteria. George Rudy/Shutterstock

Health starts in the mouth, experts say, and there are many layers to this idea. According to a 2021 report on “Oral Health in America,” by the U.S. Department of Health and Human Services, the condition of your mouth plays a vital role in your physical, mental, and even financial health.

According to the Mayo Clinic, your mouth provides “a window to your overall health.” Studies suggest that when the mouth shows signs of illness and inflammation due to an infection, organs and tissues deeper inside the body can soon suffer a similar fate. In traditional Chinese medicine, examining the mouth is seen as a critical part of diagnosing disease or evaluating a person’s well-being.

This window of the mouth can be seen at the microscopic level with bacteria and other disease-causing microbes the mouth is able to spread.

For example, if mouth bacteria from gum disease (periodontitis) move to the heart, it can lead to endocarditis (an infection in the lining of your heart). If these infectious mouth microbes move to the lungs, they may trigger respiratory disease. If you’re pregnant, it can cause problems for your baby.

It’s clear that bacterial overgrowth can spread disease, but keep in mind that not all bacteria are bad. Just think about the observations researchers have made into the body’s microbiome.

As scientists have come to understand the microbiome more deeply over the past few decades, it has given rise to a new understanding in modern medicine. We now know that people are more than just cells living in an impossibly complex symmetry; we’re also teeming with a variety of bacterial and microbial life.

It may sound a little unsettling at first, but our health depends on these symbiotes. The microbiome, as it’s called, trains our immune system, aids in our digestion and assimilation of food, and keeps potentially dangerous microbes at bay.

Traveling Mouth Microbes

These “friendly” microbes are found all over our bodies. However, the heart of it lies in our gut.

But keep in mind that we also have a pretty sizable microbiome in our mouths, as well. The human oral cavity hosts the second-most plentiful and diverse microbiota in the body after the gastrointestinal tract. And many of the bacterial strains found in the mouth can also benefit the rest of the body.

For years, researchers recognized the presence of mouth microbes, but the colony was primarily believed to be its own little universe, having little influence or exchange with our gut flora.

The rationale for this belief was that mouth microbes were considered to be too weak to make the trip because stomach acid and bile would destroy them on the way down.

If microbes were able to make it past these acidic barriers, doctors and scientists thought it was a sign of trouble, manifesting in diseases such as rheumatoid arthritis, inflammatory bowel disease, and colon cancer.

But the National Library of Medicine highlighted a study published in 2019 that tells a different story—one in which friendly microbes are much heartier than scientists previously believed.

Instead of reinforcing the notion that oral microbes traveling to the intestines intact was a rare event and a hallmark of disease, these researchers found that microbes regularly made the trip unscathed. In fact, successful journeys were found to be pretty normal. Researchers looked at hundreds of microbe strains (both salivary and fecal) from 470 individuals in five countries and found evidence for a vast majority of oral species to be transferable.

Instead of the mouth being a lone microbial island meant to be separate from the rest of the body, scientists concluded that the mouth was “an endogenous reservoir for gut microbial strains.”

So your mouth shares bacteria with your gut, but both regions are also meant to be unique microbial environments. Researchers found that disease-causing bacteria showed a higher rate of crossover between oral and gut microbes. Compared to healthy individuals, colon cancer patients showed increased levels of microbe transmission, particularly among the strains associated with colon cancer.

Ancient Diets, Better Microbes

It’s estimated that between 50 billion and 100 billion bacteria reside inside your mouth, both good and bad. Some strains work in favor of your health, and some can run you down.

The ratio between health-promoting and disease-causing bacteria depends on several factors, but your daily decisions play an enormous role in determining which bacteria proliferate in your mouth (and possibly make their way into the rest of your body.)

Of course, good oral hygiene can play a significant part in reducing periodontal disease and improving the overall health of our mouth microbiome. But scientists have also shown that the quality of our oral-bacterial landscape is largely dictated by what we eat.

Our collective oral landscape has certainly degraded with time. Everyone is familiar with the notion that the modern diet has had a detrimental effect on public health. But consider the damage from a microscopic level.

A 2013 study published in Nature Genetics showed that our ancient prehistoric ancestors had a far better composition of oral bacteria than modern folks.

Researchers looked at the teeth of 34 prehistoric human skeletons and found that as mankind went from the hunting and gathering lifestyle to agriculture, disease-causing bacteria began to spread. The trend only worsened when our diets became more dependent on great quantities of processed flour and sugar in the modern era.

Researchers concluded that moving from a diet of vegetables and game to one of increasingly simpler carbs and processed meat shifted the composition of our mouth microbiome for the worse. The study showed that the modern diet has conspired to create an ecosystem low in microbe diversity, and it caters to those strains related to opportunistic pathogens.

A 2015 study arrived at a similar conclusion. Scientists ran CT scans on the plaster casts of Pompeii residents who died in the ash of the legendary Mt. Vesuvius eruption 1900 years ago. Researchers remarked on the fine teeth found in the mouths of these ancient individuals, both rich and poor. Regardless of their position in society, subjects were found to have diets rich in vegetables. They possessed none of the benefits of modern dentistry.

Feeding A Good Colony

So what should we be eating to ensure our mouth (and our health in general) has a health-promoting microbiome, and what foods should we avoid?

A 2022 study in the journal Nutrients offers some insight.

Scientists looked at the influence of diet on the oral environment, particularly in regard to the development of periodontal disease. They noted that things such as excess sugar consumption and antibiotic use are major culprits, but that the foods with the greatest impact on disease turn out to be those found in abundance in the modern diet: farmed animal meats, high-sugar dairy products, refined vegetable oils, and processed grains.

Excesses in these foods led to extremes in the microenvironment of the mouth. Too much animal protein was found to contribute to a mouth with an exceedingly acidic pH, and simple carbs contributed to inflammation. It’s this acidic-inflamed environment that best supports the microbial strains that leads to periodontal disease.

For a healthier mix of mouth microbes, scientists showed support for wild foods, such as game, berries, and uncultivated root vegetables. However, for those who don’t have the time or opportunity to hunt and gather, researchers pointed to a large, cross-sectional study looking at the association between diet and periodontitis.

“That study found that a dietary pattern rich in fruits, vegetables, salad, water, and tea and with limited intake of fermentable carbohydrates, fatty acids, protein, and sugar-rich beverages had a lower extent of periodontal disease,” researchers wrote. “This is attributable to reduced expression of periodontal bacteria in the oral microenvironment.”