Two people who share a birthday can be aging at very different speeds under the hood. A new study from the University of Hawaii at Manoa suggests part of that difference may be sitting in the gut.
In 123 adults, differences in gut bacteria were tied to about 15 percent of the variation in how fast participants were aging biologically. The findings appeared in Scientific Reports on July 14, 2026.
The team measured biological aging with DunedinPACE, a DNA methylation biomarker developed from the long-running Dunedin cohort in New Zealand. Rather than guessing someone's age from a blood sample, it estimates how fast their body is actually deteriorating.
That is a notable design choice. Most epigenetic "clocks" compare people of different ages at one snapshot in time. DunedinPACE was built to isolate the pace of aging within individuals, and shows strong test-retest reliability.
Also read: Seven days of deep meditation may trigger brain changes similar to psychedelics
Two bacteria stood out
When the Hawaii team looked at which microbes tracked with faster or slower aging, two names surfaced. Bifidobacterium adolescentis, a fiber-fermenting resident of the adult colon, showed one of the clearest links to a slower pace of aging.
On the other end, Succinivibrio dextrinosolvens had one of the strongest associations with faster biological aging. The study is correlational, and the authors are careful about the limits of what 123 people can prove.
"This study advances our understanding of the relationship between the gut microbiome and biological aging," senior author Alika K. Maunakea, a professor at the John A. Burns School of Medicine at UH Manoa, said in a university statement.
He framed the finding as an early step toward understanding the gut microbiome's role in healthy aging. The cohort notably included Native Hawaiian and Pacific Islander participants, groups historically underrepresented in aging and microbiome research.
Also read: The everyday habits that could raise your dementia risk
Why the gut-aging link is plausible
The gut is not just a digestive tube. Its bacteria ferment fiber into short-chain fatty acids that influence inflammation, metabolism and immune signaling, all systems that shape how the body ages.
That biological plausibility is one reason the microbiome has drawn so much attention in longevity research. Lead author Braden P. Kunihiro, a first-year medical student at JABSOM, pointed to the everyday relevance.
"The gut microbiome is highly responsive to lifestyle, diet, environment and other everyday exposures," he said.
What this means in practice
The study does not hand out a diet plan, and readers should not treat it as one. But it fits a wider pattern in aging research.
Also read: Your cells age faster with these habits - and some of the damage may be reversible
Habits that feed a diverse gut community, such as plant fibers, legumes, whole grains and resistant starches, are the same habits already linked to lower risk of chronic disease. The take-home from Hawaii is modest and honest.
Gut bacteria appear to be part of the biological aging story, not the whole of it. Anyone with specific concerns about aging, metabolism or gut health should talk with their own doctor before making bigger changes.
Also read: The cholesterol marker most doctors don't routinely test may be raising your heart risk