Here's what to eat to protect your mouth's good bacteria

Your oral microbiome is the key to a healthy mouth and body. Here's how to make sure it's well-nourished.

Everyone knows that sugary foods can lead to dental cavities, by feeding harmful bacteria in our mouths. But it turns out that keeping them away is as much about what you do eat as what you don't eat – and from fruit to cheese, the most beneficial foods might surprise you.

Research is starting to uncover the importance of the oral microbiome. This community is made up of 700 different bacterial species, as well as viruses, fungi, and other microorganisms. It can have a profound effect on our health. Currently, though, it's often neglected.

It doesn't have to be this way. It's easy to take care of your mouth microbes – and as with the gut, your diet is a major factor. Here's what you need to know to eat your way to healthy teeth. 

In the bustling neighbourhood of your mouth, microbes carve out ecological niches, with each species preferring a distinct habitat. While some bacteria choose to inhabit the surface of teeth, others might prefer the tongue or lurk in the tiny crevices between your teeth and gums.

Some of these microbes are bad news. Take Streptococcus mutans, which sits on the surface of teeth and loves to eat sugar. This bacterium turns sugars into acids that eat away at the protective enamel on teeth. Eventually this can lead to holes or cavities, which more than 80% of Americans have by the time they enter their mid-30s. 

Other mouth microbes are actively helpful. For instance, if beneficial bacteria such as Veillonella, Actinomyces, some species of Streptococcus, or Neisseria make your mouth their home, they can prevent harmful pathogenic strains from colonising.

Having a good oral microbiome isn't just important for dental health. If you don't brush your teeth regularly or fastidiously enough then small pockets can form in the space between teeth and gums. In this oxygen-poor environment, bugs such as Porphyromonas gingivalis can thrive.

Once there, P. gingivalis causes gum disease, but also raises 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 poor oral microbiome to colon and pancreatic cancer.

In one recent study, a team of scientists from across the US tested the saliva of participants and then followed up to identify their subsequent risk of cancer. Those whose oral microbiome contained certain bacterial species linked to tooth decay or Candida yeast were found to have a higher risk of pancreatic cancer.

There's also emerging evidence that, as with the gut, it's important to have a varied mix. For instance, one recent study found that a lower diversity of microbes in the mouth is associated with depression.

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

What to eat – and what to avoid

Snacks or beverages to avoid are those primarily made up of lots of sugar, as these are gobbled up by cavity-causing bacteria. It's also a good idea to limit your intake of processed carbohydrates, as these are easily broken down into sugars in the mouth.  Starchy snacks to avoid include white bread, crackers, biscuits, cakes, and pretzels.

Attracting "good" bacteria is helpful for two reasons. They compete for food and space with those that are linked to cavities and disease, reducing their populations. But some also directly attack the ones you don't want moving into your........

© BBC