Foods that may protect your oral health

From leafy greens and cheese to tea and fermented foods, scientists are finding that diet may play a bigger role in maintaining a healthy oral microbiome than previously thought.

For years, advice on maintaining healthy teeth has been straightforward: Brush twice a day, clean between your teeth, limit sugar and visit a dentist regularly.

But scientists are increasingly looking at another part of the equation — the trillions of microorganisms that live in and around the human body, including hundreds of species found in the mouth.

Known collectively as the oral microbiome, these microorganisms live on the teeth, tongue, gums and in the tiny spaces between teeth.

Some can contribute to cavities and gum disease, while others may protect the mouth by competing with harmful bacteria.

Emerging research suggests that what people eat can influence this microbial community, potentially affecting not only oral health but other aspects of the body.

The message is not simply to eat less sugar, researchers say.

It is also about eating foods that create conditions in which beneficial microorganisms can survive and compete with harmful ones.

• A microscopic community

The human mouth is home to an estimated 700 different types of microorganisms, including bacteria, fungi and other microscopic organisms.

They do not all live in the same place or behave in the same way.

Some bacteria thrive on the surface of teeth, others prefer the tongue, while others live around the gums or in the narrow spaces between teeth.

One of the best-known bacteria involved in tooth decay is Streptococcus mutans.

It feeds on sugar and converts it into acids that gradually damage the hard protective surface of teeth.

Repeated exposure to these acids can eventually produce cavities.

But the oral microbiome also contains microorganisms that can help protect against disease.

Species belonging to groups such as Veillonella, Actinomyces, Streptococcus and Neisseria can compete with harmful bacteria for nutrients and space.

Some can also produce substances that inhibit potentially dangerous microorganisms.

Laura Weyrich, a researcher at Pennsylvania State University in the United States who studies oral microbes and their evolution, says the relationship between these microorganisms can be surprisingly complex.

Within the large family of Streptococcus, for example, some bacteria consume sugar but produce less acid than others.

Some may even interfere with bacteria that produce larger quantities of acid.

Another example is Streptococcus salivarius, which can produce antimicrobial substances capable of inhibiting a range of other microorganisms.

The implication is important: a healthy mouth is not necessarily a bacteria-free mouth.

Instead, it may depend on maintaining the right balance and diversity of microorganisms.

• When the balance is disturbed

Poor oral hygiene can allow plaque to accumulate and pockets to form between the teeth and gums.

These areas can become low in oxygen, creating favourable conditions for bacteria such as Porphyromonas gingivalis.

The bacterium is associated with periodontal disease, a serious infection and inflammation of the tissues supporting the teeth.

Researchers have also found associations between P. gingivalis and a number of conditions affecting other parts of the body, including cardiovascular disease, diabetes, Alzheimer's disease, depression, inflammatory bowel disease and rheumatoid arthritis.

It has also been linked to pregnancy complications such as premature birth.

More recently, scientists have been investigating possible relationships between the oral microbiome and cancer.

Research has reported associations between changes in oral microorganisms and colorectal and pancreatic cancers.

In one recent study, researchers analysed saliva from participants and followed them over time.

They found that people carrying certain microorganisms associated with dental decay or Candida fungi had a higher likelihood of developing pancreatic cancer.

Such findings should be interpreted cautiously. An association does not necessarily mean that the bacteria caused the disease.

Nevertheless, the research is adding to a growing scientific interest in the possibility that the mouth may provide clues about — or even influence — health elsewhere in the body.

• Sugar remains a major concern

For consumers, one of the clearest lessons remains familiar: cutting down on added sugar is important.

Sugary foods and drinks provide fuel for acid-producing bacteria associated with tooth decay.

Highly processed foods can also contribute to the problem.

Foods such as white bread, biscuits, sweet pastries and other refined carbohydrates can be rapidly broken down into sugars in the mouth.

Frequent exposure may be particularly damaging because it gives acid-producing bacteria repeated opportunities to create an acidic environment around the teeth.

But researchers say the solution is not simply to remove foods from the diet.

Some foods may actively support a healthier oral microbiome.

• Leafy greens and nitrate

Leafy vegetables such as kale and spinach, as well as beetroot and radishes, are rich in dietary nitrate.

Certain bacteria in the mouth, particularly species of Neisseria, can convert nitrate into nitrite.

The process continues elsewhere in the body and contributes to the production of nitric oxide, a molecule involved in blood-vessel function and blood-pressure regulation.

This illustrates one of the most intriguing aspects of the oral microbiome: microorganisms in the mouth can participate in biochemical processes that have effects beyond the mouth.

In one study, older adults who consumed nitrate-rich beetroot juice twice a day for two weeks experienced lower blood pressure.

That does not mean beetroot juice should be considered a treatment for hypertension.

Rather, the findings provide an example of how oral bacteria can interact with compounds in food and influence processes elsewhere in the body.

• Tea, berries and plant compounds

Many plant foods contain polyphenols, naturally occurring compounds that help plants cope with environmental stress.

Scientists are increasingly interested in their possible effects on the microorganisms in the human mouth.

Research by Christine Wu, a professor of pediatric dentistry at the University of Illinois Chicago, has examined how food-derived compounds affect oral bacteria.

Her work suggests that polyphenols found in tea can inhibit bacteria associated with cavities and gum disease.

They may also interfere with the ability of bacteria to attach to teeth and contribute to dental plaque.

Tea may have another benefit.

Research suggests that drinking tea can reduce some bacteria associated with bad breath, particularly microorganisms found towards the back of the tongue.

Berries and other dark-coloured fruits are also rich in polyphenols.

Cranberries, in particular, have attracted scientific interest.

Studies suggest that compounds in cranberries may interfere with plaque formation and reduce some bacteria associated with cavities and gum disease.

Honey also contains polyphenols and has shown antimicrobial properties in research.

However, this should not be interpreted as a licence to consume large amounts of honey.

Honey is still a source of sugar, and frequent sugar exposure remains a major risk factor for tooth decay.

• Why cheese could be good for your teeth

Cheese may be another unexpectedly useful food for oral health.

In a small study conducted in Italy, nine people ate Grana Padano cheese daily for five days.

Researchers observed modest changes in the composition of their oral bacteria.

Levels of S. mutans, which is strongly associated with tooth decay, declined, while S. sanguinis, a microorganism more commonly found in healthy mouths, increased.

Cheese may also help in a simpler way: chewing stimulates saliva production.

Saliva helps wash away food particles and sugars and can neutralise acids produced by bacteria.

Christine Wu notes that cheese combines the nutritional properties of dairy with the mechanical benefits of chewing and increased saliva flow.

• Fermented foods enter the picture

Fermented foods may provide another potential benefit.

Products such as kefir contain live microorganisms that may compete with harmful bacteria.

A recent review of research found that kefir may reduce some disease-causing microorganisms in the mouth and interfere with the formation of dental plaque.

But scientists caution against searching for a single food that can “fix” the oral microbiome.

Gaetano Isola, a professor of dentistry at the University of Catania in Italy, argues that the overall pattern of eating matters more.

A diet dominated by refined sugars and highly processed carbohydrates can favour microorganisms that are particularly good at producing and tolerating acids.

Over time, this may disturb the balance of the oral microbial community.

By contrast, diets rich in minimally processed plant foods, whole grains and nutrient-dense foods, while limiting frequent consumption of refined sugar, may create conditions that favour a healthier microbial balance.

• Lessons from the Mediterranean diet

Research involving Isola has also examined the relationship between dietary patterns and periodontal disease.

People who more closely followed a Mediterranean-style diet — rich in fruits, vegetables, whole grains and healthy fats — tended to have less severe periodontal disease.

Those who followed the diet less closely, particularly people who frequently consumed red meat, were more likely to experience severe periodontal disease.

Researchers are still investigating why.

One theory is that compounds associated with red meat and its digestion may contribute to an environment that favours bacteria such as P. gingivalis.

The evidence is not yet strong enough to conclude that eating red meat directly causes gum disease, but the association is an area of continuing research.

• Brushing still comes first

For all the excitement surrounding the oral microbiome, dentists are not suggesting that people replace basic oral hygiene with a particular diet.

Brushing and cleaning between the teeth remain essential.

Cleaning between teeth has been associated with reductions in S. mutans, while brushing the teeth and tongue can significantly reduce microorganisms associated with oral disease.

Mouthwash is more complicated.

Scientists are still trying to understand how frequent use of antimicrobial mouthwashes affects the wider microbial community.

Some mouthwashes are designed to kill bacteria broadly, while future treatments could potentially be designed to restore a healthier microbial balance.

Chlorhexidine, for example, can be useful for treating certain oral conditions over a short period, but research has also shown that it can disrupt the composition of the oral microbiome when used.

• A practical message for families

The science of the oral microbiome is still evolving.

Researchers do not yet understand all the interactions between food, oral bacteria and diseases elsewhere in the body.

But the evidence is increasingly pointing towards a simple principle: oral health is not only about removing harmful bacteria.

It is also about supporting a diverse and balanced microbial community.

For families, that does not require an expensive or complicated diet.

A healthier approach means eating more vegetables, particularly leafy greens; Choosing whole grains and minimally processed foods; Including nutritious sources of protein; and reducing added sugar, especially sugary drinks.

Tea, vegetables, fruits, cheese and fermented foods may all have a place in such a diet.

The most important factor, however, is the overall pattern.

As Weyrich puts it, the advice may sound familiar: Maintain a balanced diet, eat plenty of vegetables and leafy greens, choose healthier sources of protein, and reduce sugar.

In other words, caring for the microscopic community in your mouth may begin with something as ordinary as what you put on your plate.

A meal of vegetables, whole grains and fruit, accompanied by some cheese and a cup of tea, may do more than nourish the body.

It could also help give the beneficial microorganisms in your mouth the environment they need to thrive.