Sugary foods are well-known culprits of cavities, but is it only sugar that raises the risk? Researchers have now found that starchy foods might also contribute to cavities. However, the risk isn't the same for everyone—it depends on a specific set of genes.

In a recent study published in the journal Microorganisms, researchers investigated how the oral microbiome responds to starch in a group of 31 participants. The oral microbiome refers to the diverse community of microorganisms such as bacteria, viruses, fungi, and other microbes that naturally live inside the mouth and contribute to oral health.

The researchers focused on a specific gene, AMY1, which codes for the enzyme salivary amylase responsible for breaking down starches in the mouth. They found that the number of copies of the AMY1 gene in an individual's DNA, when combined with the presence of starch, influenced the composition of bacteria in the oral microbiome.

"Most people have been warned that if you eat a bunch of sugar, make sure you brush your teeth. The takeaway finding here is that depending on your AMY1 copy number, you may want to be just as vigilant about brushing your teeth after eating those digestible starches," said Angela Poole, senior author of the study in a news release.

For the study, researchers collected saliva samples from participants with varying numbers of AMY1 gene copies and introduced starch into the cultured samples. This allowed them to observe how the bacterial composition changed when starch was added.

They discovered that, in general, the diversity of bacteria decreased with the addition of starch. In samples with a higher number of AMY1 copies, the starch caused a significant reduction in Atopobium and Veillonella bacteria while the levels of Streptococcus increased. These bacteria are all linked to tooth decay and gum disease.

"Some increased and some decreased, so it's not so straightforward as saying, 'The whole thing is good or bad. It's an interaction, but it looks like the AMY1 copy number, as well as which species are present in people's mouths when they eat starch, is affecting the risk for developing these diseases," Poole said.

The researchers also noted that the oral microbiome has evolved alongside the AMY1 gene, with higher copies found in populations with a long history of starch consumption.

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