People have long given up on the search for the Fountain of Youth, a mythical spring that could reverse aging. But for some scientists, the hunt has not ended – it’s just moved to a different place. These modern-day Ponce de Leóns are investigating whether gut microbes hold the secret to aging well.

The gut microbiome refers to the vast collection of microscopic organisms – bacteria, fungi and viruses – that largely inhabit the colon. These microbes aid in digestion and produce molecules that affect your physiology and psychology. The composition of the microbiome is influenced by a combination of factors, including genetics, diet, the environment, medications and age.

I’m a microbiology professor and author of “Pleased to Meet Me: Genes, Germs and the Curious Forces That Make Us Who We Are,” which describes how the gut microbiome contributes to physical and mental health. The discovery that the gut microbiome changes with age has ignited studies to determine whether the Fountain of Youth might be right under your nose, down inside your gut.

You’re only as old as your gut microbes

People are most familiar with outward signs of aging, such as wrinkles and graying hair, but there are also microscopic changes taking place deep inside. The gut microbes of older people tend to be less diverse, with more bacteria that promote inflammation and other hallmarks of aging. Changes to the microbiome across age are so consistent that algorithms can reliably predict a person’s age based on their microbiome composition.

There are exceptions to this rule. Older adults and supercentenarians who age........

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