We all know that eating too much sugar can lead to cavities, but new research suggests that starchy foods might also play a role—depending on your genes.

A study published on February 19 in Microorganisms found that a specific gene called AMY1 influences how starch affects the bacteria in your mouth. This could impact your risk for cavities and gum disease.

AMY1 is a gene that helps your body produce salivary amylase, an enzyme that breaks down starch in the mouth.

Some people have more copies of this gene than others, which affects how efficiently their bodies process starchy foods like bread, rice, and pasta.

Researchers collected saliva samples from 31 people with different AMY1 gene copies and added starch to see how bacteria reacted.

They found that the presence of starch changed the balance of bacteria in the mouth.

In samples with a high number of AMY1 copies, the amount of certain bacteria, such as Atopobium and Veillonella, decreased, while Streptococcus increased. All three bacteria are linked to tooth decay or gum disease.

“It’s not as simple as saying starch is bad for your teeth,” said Angela Poole, senior author and assistant professor at Cornell University.

“The way starch affects your oral health depends on how many copies of AMY1 you have and the types of bacteria already in your mouth.”

Since people with more AMY1 copies break down starch more efficiently, they produce more sugar in their mouths. This can encourage bacteria like Streptococcus to grow, which may contribute to cavities and gum disease.

“If you have a high AMY1 copy number, you may want to be just as careful about brushing your teeth after eating starchy foods as you are with sugary foods,” Poole said.

The researchers also discovered that populations with a long history of eating starchy foods—such as those from agricultural societies—tend to have more AMY1 copies.

This suggests that over time, human bodies adapted to process starch better. However, as a result, their oral bacteria also adapted, which may influence oral health risks today.

While sugar remains a well-known culprit for cavities, starch could also play a role—especially for people with a high AMY1 copy number. Good oral hygiene, including brushing and flossing after meals, is key to keeping your teeth healthy, no matter what’s on your plate.

Source: Cornell University.