Can Your Gut Microbiome Reveal How Well You’re Aging? What a New Study Found

We usually think of ageing as something written on our birth certificate. The older you are, the more your body drifts into a low, simmering state of inflammation — scientists even have a name for it: “inflammaging.” It is thought to feed many of the diseases of later life, from diabetes to heart disease.

But everyone knows a 45-year-old who seems 30, and a 30-year-old who seems 50. A new study in Nature Communications asked a simple question: when it comes to inflammation, what matters more — how old you are, or which bacteria live in your gut?

The result was striking.

For some inflammatory and physiological markers, young adults with the “Bacteroides 2” enterotype showed an inflammaging-like profile that other enterotypes reached up to about 37 years later. This is not the same as being biologically 37 years older.

What the study found

1. Gut microbiota composition outperformed age for most measured outcomes. Danish researchers measured 30 inflammation-related proteins in the blood, plus 19 biochemical and physiological measures such as BMI, body fat, cholesterol, blood sugar, blood pressure and cardiorespiratory fitness, and matched them with stool microbiota profiles. Chronological age was associated with about 40% of the inflammatory cytokines. But microbiota composition explained more variation than age for 29 of 30 cytokines (97%) and 16 of 19 physiological variables (84%). This does not mean age was relevant to only one marker; it means the microbiome explained more variance than age for 29 of 30.

2. Researchers grouped the gut communities into four broad enterotypes. These are research-based community patterns, not fixed biological types like blood groups. The four clusters were Bacteroides 1 (34%), a high-diversity Richness type (30%), Prevotella (19%) and Bacteroides 2 (17%).

People with Bacteroides 2 stood out. Even after accounting for age, they had higher levels of classic inflammation signals — IL-6, TNF-α and CRP among them — plus higher BMI and triglycerides, lower “good” HDL cholesterol and lower fitness. Their numbers were still within normal clinical ranges, but sat consistently closer to the edge.

The most striking finding was that, for some markers, a 20-year-old with Bacteroides 2 already had levels that people with other enterotypes reached around 37 years later. The safest interpretation is that this enterotype was associated with an earlier inflammaging-like profile — not that the person's whole body was literally 37 years older.

3. That gut type was associated with higher future disease risk. The team linked participants to Denmark's national hospital records for up to about nine years. People with Bacteroides 2 had a 21% higher relative hazard of receiving a new hospital diagnosis (hazard ratio 1.21) across seven disease chapters, including circulatory, digestive, respiratory, musculoskeletal, nervous-system, eye and infectious diseases. Mediation analyses suggested that inflammatory cytokines accounted for part of this association — around 4% overall, with larger proportions for some respiratory and infectious outcomes.

4. Higher diversity was associated with a more favorable profile. People with the high-diversity Richness enterotype had the lowest CRP, lower BMI and triglycerides, and a 21% lower relative hazard of new diagnoses (hazard ratio 0.79). Several taxa enriched in this group, including members of the Ruminococcaceae family and the Eubacterium siraeum group, include organisms known from other research to produce butyrate. This study did not show that butyrate itself caused the lower inflammatory or disease-risk profile.

Several key enterotype–inflammation associations were also reproduced in the independent European MetaCardis cohort. That strengthens confidence in the inflammatory pattern, although the Danish registry-based future-disease findings were not simply replicated as a second prospective cohort.

Relative hazard of a new hospital diagnosis during follow-up, compared with the other enterotypes. These are associations, not proof that the microbiome caused the difference.

Now the part the headline can't fit

It shows a link, not a cause. The authors make this clear. The microbiome could contribute to inflammation, but inflammation, adiposity, medicines, diet or other lifestyle factors could also shape the microbiome. The study cannot establish which came first.

Diet is an important confounder. What we eat shapes both the gut microbiome and systemic inflammation. The study had only broad dietary categories, so some of the apparent microbiome association may reflect underlying diet or other lifestyle patterns.

One stool sample, one snapshot. Gut bacteria were measured once, with a method (16S sequencing) that identifies bacteria mostly at the genus level. Gut communities shift with diet, medicines and illness, and a single sample may not represent someone's usual gut.

“37 years earlier” is not a biological age. It applies to a handful of markers, and the differences between gut types largely faded by around age 65. It does not mean a person's body is 37 years older.

The population was fairly narrow. Participants were Danish-born adults living near Copenhagen, and participation was selective. Results may differ in populations with different diets, ethnic backgrounds, healthcare systems or baseline disease patterns.

And “good bacteria” is not so simple. One of the genera linked to higher inflammation was Lactobacillus — the very name on many probiotic labels. That doesn't mean probiotics are harmful, but it's a reminder that you can't reduce gut health to a single bacterial name on a bottle.

This post is a plain-language summary of published research and is not medical advice. It describes an observational study, so it cannot show that changing gut bacteria changes disease risk. Talk to your doctor before making major changes to your diet, supplements or medicines.

Source
Eriksen C, Chatzigiannidou I, Dehli RK, et al. Gut microbiota composition outperforms chronological age in predicting systemic inflammation and incident disease risk. Nature Communications. Published 8 September 2026. doi:10.1038/s41467-026-77499-9