Your gut contains billions of bacteria that help regulate everything from digestion to immune system functionality, yet scientists still don’t know much about your microbiome. They aren’t sure how it can change over time, or even what a “normal” one looks like. However, new research on gut bacteria has come to one conclusion: the microbiome does a fantastic job at predicting peoples’ ages. 

Researchers at InSilico Medicine, a Rockville, Maryland–based artificial intelligence startup, trained a computer to analyze more than 3,600 samples of gut bacteria from 1,165 healthy adults across the world. The program -- which analyzed 95 different species from 90% of samples, as well as the age of the people they had come from -- was able to accurately predict someone’s age within 4 years. It also determined that 39 of the 95 types of bacteria were most important in predicting age.

Researchers analyzed the results and found that some microbes became more abundant or less abundant as people aged. They also believe changes in diet, sleep habits, and physical activity likely contribute to bacterial shifts. Scientists say this “microbiome aging clock” could be used as a baseline to test how fast or slow a person’s gut is aging and whether things like alcohol, antibiotics, probiotics, or diet have any effect on longevity. It could also be used to compare healthy people with those who have certain diseases, like Alzheimer’s, to see whether their microbiomes deviate from the norm.

If the idea is validated by other studies, it would be added to the list of biomarkers used to predict biological age and changes to DNA expression over a lifetime. Together, these tools can help researchers better test whether certain interventions -- for example, drugs and other treatments -- have any effect on the aging process.