As we age, the trillions of microbes living in our gut change. The beneficial bacteria, Bifidobacterium, Faecalibacterium prausnitzii, decline. Pro-inflammatory species rise. The immune cells lining the large intestine begin to malfunction, and the gut wall becomes leaky, feeding a chronic low-grade inflammation called inflammaging that is now recognized as a driver of many age-related diseases.
The question is whether we can do anything about it.
A review published in Nature Reviews Endocrinology by Andrea Ticinesi and colleagues at the University of Parma lays out the evidence. The paper, which comprehensively reviews the gut microbiome’s role in aging trajectories, concludes that the microbiome’s causal role in defining the pace of aging “is still uncertain in clinical terms”, but the potential is too large to ignore.
The aging gut undergoes several well-characterized changes:
- Loss of diversity: Microbial richness declines, with a shift from anti-inflammatory taxa (Bifidobacterium, Lactobacillus, Faecalibacterium) toward pro-inflammatory species (certain Enterobacteriaceae)
- Immunosenescence: Immune cells in the gut lining age and malfunction, reducing their ability to maintain tolerance to commensal bacteria
- Increased permeability: The gut barrier becomes leakier, allowing bacterial products like lipopolysaccharide (LPS) to enter the bloodstream and fuel systemic inflammation
- Reduced SCFA production: Short-chain fatty acids (acetate, butyrate, propionate), which are critical for immune regulation and colon health, decline
The review frames the gut microbiome not just as a passive marker of aging but as an active participant: it provides antigenic stimulation to the senescent immune system, potentially accelerating the very inflammaging it might otherwise protect against.
The centenarian exception
A striking counterexample comes from María Branyas Morera, who died in 2024 at 117 years and 168 days, the world’s oldest verified person. A study in Cell Reports Medicine (2025) led by Manel Esteller’s team at the Josep Carreras Leukaemia Research Institute in Barcelona examined her multi-omics profile.
Her gut microbiome was dominated by Actinobacteriota, especially Bifidobacterium, bacteria that typically decline with age. Her genome carried longevity-associated variants, and her epigenetic age was significantly younger than her chronological age. The researchers noted that she ate three portions of natural unsweetened yogurt daily, potentially replenishing her Bifidobacterium populations.
The study is N = 1, a fascinating data point, not a clinical trial, but it illustrates the kind of microbiome profile associated with extreme longevity.
What the trials show
Mediterranean diet, the strongest evidence
The NU-AGE trial, one of the largest dietary interventions in older adults, assigned 612 participants aged 65,79 across five European countries to a tailored Mediterranean diet for 12 months. Published in Gut (2020), the study found that diet adherence was associated with favorable microbiome changes, increased short-chain fatty acid production, reduced secondary bile acids, and those changes correlated with lower frailty markers and improved cognitive function.
The effect was indirect: diet adherence did not directly reduce frailty, but the microbiome changes it produced did. The conclusion: a Mediterranean diet is probably the most reliable way to shift the aging microbiome in a healthier direction.
Probiotics for muscle and brain
A 16-week randomized trial of 123 sarcopenic men found that a daily high-dose probiotic (Vivomix, 112 billion CFU) improved muscle strength and quality-of-life scores compared to placebo. A meta-analysis of 7 RCTs (733 older adults) confirmed improvements in muscle mass (SMD = 0.962) and strength (SMD = 1.037), but with very high heterogeneity (I² ≈ 89%), meaning the results are not consistent enough to draw firm conclusions.
In mild cognitive impairment, a small 12-week trial (42 patients, 2023) found that probiotics improved cognitive function and sleep quality. A larger 12-month trial is now underway testing three specific Lactobacillus strains.
The meta-analysis
The most comprehensive analysis to date, Zhuang et al., a systematic review of 29 RCTs (1,633 participants) published in Nutrition Journal (2025), found:
- Probiotics alone: Increased Bifidobacterium (SMD = 0.40), but no significant anti-inflammatory effects
- Prebiotics alone: Stronger Bifidobacterium increase (SMD = 1.09) and anti-inflammatory cytokine changes (IL-10 up, IL-1β down)
- Synbiotics (prebiotic + probiotic): The strongest effects, including reduced TNF-α and increased short-chain fatty acid production
The caveat: when high-bias studies were excluded, the probiotic effects on Bifidobacterium became non-significant. High heterogeneity and small sample sizes plague the field.
What about postbiotics?
Postbiotics, non-viable bacterial products or metabolites, are the newest entrant. The advantage is stability: they do not require live organisms to survive the gut. But the evidence base is thin. No large trials have tested postbiotics specifically for aging-related outcomes. The field is watching.
The limits
The Ticinesi review is explicit about the uncertainty: the microbiome’s causal role in defining aging trajectories “could be context specific.” High inter-individual variability means what works for one person may not work for another. At-home microbiome testing kits, increasingly popular, remain unreliable, a NIST evaluation of 7 commercial tests found discrepancies between providers as large as the biological differences between individuals.
The bottom line
The strongest evidence supports dietary change, a Mediterranean-style diet, as the most effective microbiome intervention for healthy aging. Probiotics show promise for specific outcomes (sarcopenia, cognition) but the evidence is inconsistent. Prebiotics and synbiotics have more consistent effects on microbiome composition but less data on clinical outcomes. Postbiotics remain experimental.
“We are not yet at the point of prescribing specific strains for specific aging outcomes,” the review concludes. “But the trajectory of the research is clear: the gut microbiome is a modifiable factor in the biology of aging, and intervening early is likely to be more effective than waiting for disease to set in.”
Source
Ticinesi A, Maggi S, Nouvenne A, Zuliani G, Franceschi C. “The gut microbiome and aging trajectories: mechanisms and clinical implications.” Nature Reviews Endocrinology, 22, 323,337 (2026). DOI: 10.1038/s41574-026-01236-x
Additional sources: Santos-Pujol E, Esteller M, et al. Cell Reports Medicine (2025); Ghosh TS, et al. Gut (2020); Zhuang K, et al. Nutrition Journal (2025); Qaisar R, et al. Calcified Tissue International (2024).