• • Author, Jasmin Fox-Skelly
  • Author’s title, BBC Future*
• Publication Date
• Reading time: 9 min

Everyone knows that sugary foods can cause cavities by feeding the harmful bacteria in our mouths. But it turns out that keeping them in check depends as much on what you eat as on what you don’t eat. And from fruits to cheese, the most beneficial foods might surprise you.

Research is beginning to reveal the importance of the oral microbiome.

This community consists of 700 different species of bacteria, as well as viruses, fungi, and other microorganisms.

It can have a profound effect on our health. However, it’s often overlooked these days.

It’s easy to take care of the microbes in your mouth, and just as with the gut, diet is a key factor. Here’s what you need to know to eat in a way that promotes healthy teeth.

In the bustling ecosystem of your mouth, microbes occupy ecological niches, and each species prefers a different habitat. While some bacteria choose to live on the surface of your teeth, others prefer the tongue or hide in the tiny crevices between your teeth and gums.

Some of these microbes are bad news. Take Streptococcus mutans, for example, which is found on the surface of the teeth and loves to consume sugar. This bacterium converts sugars into acids that erode the protective tooth enamel. Over time, this can lead to cavities.

Other oral microbes are actively beneficial. For example, if beneficial bacteria such as Veillonella, Actinomyces, certain species of Streptococcus, or Neisseria make your mouth their home, they can prevent harmful pathogenic strains from taking hold there.

Other Consequences

Having a healthy oral microbiome isn’t just important for dental health.

If you don’t brush your teeth regularly or thoroughly enough, small pockets can form in the space between your teeth and gums. In this low-oxygen environment, microorganisms such as Porphyromonas gingivalis can thrive.

Once there, P. gingivalis causes gum disease, but it also increases the risk of health problems such as cardiovascular disease, depression, Alzheimer’s disease, diabetes, inflammatory bowel disease, rheumatoid arthritis, and even preterm birth.

In recent years, scientists have increasingly linked a dysfunctional oral microbiome to colon and pancreatic cancer.

In a recent study, a team of scientists from across the United States analyzed participants’ saliva and subsequently assessed their risk of developing cancer.

They found that participants whose oral microbiome contained certain bacterial species associated with tooth decay or yeasts of the genus Candida had a higher risk of pancreatic cancer.

Evidence is also emerging that, as with the gut, it is important to have a diverse mix of microorganisms. For example, a recent study found that lower microbial diversity in the mouth is associated with depression.

But, crucially, brushing your teeth alone is not enough to maintain this microbial community. Whatever you eat, they eat too, and that has a direct effect on which ones can thrive.

What to Eat and What to Avoid

Snacks or drinks to avoid are those consisting mainly of large amounts of sugar, since the bacteria responsible for cavities feast on them.

It’s also advisable to limit your intake of processed carbohydrates, as they break down easily into sugars in the mouth. Starchy snacks to avoid include white bread, crackers, cookies, cakes, and pretzels.

Promoting the growth of “good” bacteria is helpful for two reasons.

They compete for food and space with the bacteria associated with cavities and disease, thereby reducing their populations. But in addition, some directly attack the bacteria you don’t want to take root in your mouth.

“Within the broader family of these sugar-loving microbes, the Streptococcus, there are some [types of bacteria] that produce virtually no acid and that, in fact, attack some of the microbes that do produce acid,” explains Laura Weyrich, an associate professor of Anthropology and Bioethics at Pennsylvania State University in the United States, who studies the oral microbiome and how it has changed throughout history.

“They’re like freedom fighters: they have their own antibiotics that they use as weapons. So, if you have these bacteria, you’re in a very good position,” says Weyrich. For example, the beneficial bacterium S. salivarius produces proteins capable of eliminating a wide variety of unwanted microbes.

These include pathogens resistant to conventional antibiotics.

If you want to cultivate a healthy oral microbiome, one of the best things you can do is eat plenty of leafy green vegetables. Foods like kale, spinach, beets, and radishes contain large amounts of nitrate, which is consumed by the Neisseria bacteria present in our mouths.

These microorganisms convert nitrate into nitrite, which is then transformed into nitric acid by other bacteria in the gut. Nitric acid circulates in the bloodstream and helps lower blood pressure, benefiting cardiovascular health. For example, in one trial, older adults who drank nitrate-rich beet juice twice a day for two weeks saw their blood pressure decrease.

Interestingly, chewing garlic—while it may not do wonders for your breath—can also benefit oral health, as it contains a chemical called allicin that attacks the bacteria responsible for cavities and gum disease.

Following a diet based primarily on plant-based foods can also benefit the oral microbiome in other ways. The reason has to do with a class of plant compounds called polyphenols.

When it gets too hot, too cold, or too sunny, animals can simply get up and move to a more favorable environment. Plants don’t have that luxury, so they produce polyphenols—special antioxidants that protect their cells and tissues from damage.

Bad Breath

However, polyphenols can also protect against harmful bacteria. For example, research has shown that the polyphenols in tea can inhibit the “bad” oral bacteria responsible for cavities and gum disease, as well as prevent them from clumping together and adhering to the surface of the teeth.

“Polyphenols inhibit one of the enzymes responsible for the adhesiveness of dental plaque,” explains Christine Wu, a professor of pediatric dentistry at the University of Illinois at Chicago College of Dentistry in the United States, whose research focuses on foods that could help combat oral pathogens.

In Wu’s study, drinking tea also appeared to inhibit the bacteria responsible for bad breath, which live at the back of the tongue.

Other foods rich in polyphenols include many fruits, especially dark-colored berries. For this reason—and contrary to what one might expect—these foods, which are high in sugar and acid, can benefit oral health.

Wu’s research has shown that drinking cranberry juice can prevent the growth of dental plaque and inhibit bacteria associated with cavities and periodontal disease.

Honey is also packed with polyphenols and has likewise been shown to prevent plaque formation and fight the bacteria that cause cavities.

Chewing cheese is also believed to offer some benefits for our oral health.

In a small study conducted by researchers in Italy, nine participants were asked to eat Grana Padano cheese every day for five days. At the end of the study, the scientists found that the genetic signatures of the bacterial communities in their mouths had changed slightly, with a lower presence of the sugar-loving S. mutans and a higher presence of S. sanguinis, a bacterium more commonly found in healthy mouths.

Cheese can also counteract some of the damage caused by S. mutans.

“Cheese is fantastic because it has all the beneficial properties of milk, but it’s solid, so chewing it increases saliva production,” says Wu. “Saliva removes some of the excess sugar from the teeth or mouth, and, since it’s neutral, it buffers the acid produced in the mouth.”

Fermented foods can also benefit the oral microbiome because they contain beneficial bacteria that compete with the “bad” ones. For example, a recent review found that drinking kefir, a fermented dairy product, could inhibit certain oral pathogens and prevent them from producing their sticky biofilm.

However, according to Gaetano Isola, associate professor of periodontology at the University of Catania in Italy, there is no single “superfood” for oral health, and what really matters is one’s overall dietary pattern.

“If we repeatedly consume refined sugars and easily fermentable carbohydrates, we favor microorganisms that are particularly efficient at producing and tolerating acids,” he says.

He explains that, over time, this can disrupt the microbial community and lead to an imbalance.

“Conversely, a diet that is generally richer in whole plant foods, fiber, and complex carbohydrates—and with less frequent exposure to refined sugars—is more conducive to maintaining a stable oral ecosystem.”

A simple practical tip from Isola is to prioritize whole plant foods—such as vegetables, whole fruits, legumes, and whole grains—over refined carbohydrates.

Mediterranean Diet

A recent study in which Isola participated found that people who adhered more closely to a Mediterranean-style diet—known for its emphasis on fruits, vegetables, whole grains, and healthy fats—tended to have less severe gum disease. Patients who adhered least closely to the Mediterranean diet tended to have more severe gum disease, especially if they frequently consumed red meat.

It is unclear what might explain the association between red meat and gum disease. One hypothesis is that protein could create an oral environment that favors harmful microbes, such as P. gingivalis.

Of course, brushing and flossing remain essential. Flossing has been associated with lower concentrations of the dental pathogen S. mutans, while brushing the teeth and tongue significantly reduces microbes linked to dental disease.

Scientists do not yet know how over-the-counter mouthwashes affect the oral microbiome. The hope is that one day they can be used to balance microbial communities rather than simply reducing the total number of bacteria present.

On the other hand, it is known that some mouthwashes containing chlorhexidine disrupt the balance of oral microbes. Even so, they can help treat gum disease and certain oral conditions in the short term.

But to achieve a healthier oral microbiome, eating the right foods is a powerful tool.

“It’s the same thing everyone always says—something that’s a bit boring: follow a balanced diet with plenty of vegetables, lots of leafy greens, lean proteins, and limit your sugar intake, especially from sugary drinks,” says Weyrich.

So why not whip up a hearty salad or a selection of excellent cheeses paired with a cup of hot tea? Not only will you be doing your body a favor—you’ll also be making the good microbes living in your mouth happy.

*This article was published on BBC Future. Click here to read the original version (in English).

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