The Gut Microbiome and Aging
What studies show about gut bacteria in older adults and centenarians, what diet and probiotic trials found, and why cause and effect are still unclear.
Content last updated . This page has not been medically reviewed.
Diet trials in older adults
In the NU-AGE trial, 612 non-frail or pre-frail older people in five European countries had their gut bacteria profiled before and after a 12-month Mediterranean-style diet designed for older adults. [3] Diet adherence was associated with specific microbiome changes, and bacteria that increased were associated with lower frailty markers, better cognitive function and lower inflammatory markers. [3] This was a diet intervention measured through the microbiome, so it cannot separate the effect of the bacteria from the effect of the diet itself. More on diet is in dietary patterns and healthy aging.Probiotics, prebiotics and synbiotics in older adults
A 2026 systematic review and meta-analysis looked at adults aged 60 and over: 14 studies (13 randomized), made up of 10 probiotic, 2 prebiotic and 2 synbiotic trials. [4] Nine studies reported a statistically significant improvement in at least one cognitive domain, and a subgroup meta-analysis found a small improvement in global cognition scores (mean difference 1.28 points, 95% CI 0.15 to 2.40). [4] The authors note heterogeneity and a shortage of high-quality studies. [4] Label: mixed; read as hypothesis-generating, and not as proof of a clinical benefit.For other uses, the NIH's NCCIH said (page last updated 2019) that probiotics may be helpful for antibiotic-associated diarrhea in young and middle-aged people, but a benefit had not been demonstrated in elderly people, according to a 2016 review of 30 studies of which 5 focused on people 65 or older. [5] Product details are in probiotic supplements explained.
What animal studies show
In mice, repeated transfers of stool material from young mice throughout life improved coordination and intestinal permeability compared with transfers from same-age mice. [6] Label: preclinical (cells/animals only). It does not show that stool transplants slow aging in people.Frequently asked questions
Does gut bacteria composition change with age?
Studies report that older people's stool bacteria differ from younger adults and vary more between individuals, and are linked with diet, residence and frailty. [1]
Do centenarians have a special microbiome?
Several reviewed studies reported higher levels of Akkermansia, Alistipes and Parabacteroides, but the systematic review says healthy-ageing signatures remain poorly defined. [2]
Can probiotics slow aging?
No source we read shows that. A meta-analysis of cognition in older adults found some positive results with heterogeneity, and NCCIH said a diarrhea benefit had not been shown in elderly people. [4][5]
Does a Mediterranean-style diet change gut bacteria in older adults?
In the 12-month NU-AGE trial, diet adherence was associated with specific microbiome changes linked with lower frailty and inflammation markers. [3]
Are stool transplants an anti-aging treatment?
Only mouse data were read: transfers from young mice improved some measures in mice. [6] Human evidence of an aging benefit was not found.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
How to read the evidence labels
Labels used on this page: established, promising but limited, mixed, insufficient evidence, preclinical (cells/animals only) and marketing claim.
What studies of older people observed
These are observational findings, which show association and not cause.- Diet, residence and frailty. In a study of 178 older people, stool bacteria formed groups that matched where people lived and how they ate. The groups correlated with frailty, other illnesses, nutrition and markers of inflammation. [1] People in long-term residential care had significantly less diverse bacteria than people living in the community, and loss of a community-type microbiota correlated with greater frailty. [1] The authors suggest diet-driven changes may be involved in different rates of health decline. [1] Because people in care differ in many ways, this does not show the bacteria caused the decline.
- Centenarians. A 2026 systematic review found that microbial signatures of "healthy ageing", separate from age-related disease, are still poorly defined. [2] Higher levels of Akkermansia, Alistipes and Parabacteroides were consistently reported in centenarians. [2] The review also notes that geographic representation was limited. [2]
Label: promising but limited as a research area; insufficient evidence that any specific bacterial pattern should be a target.
Safety and limits
- The NCCIH notes severe or fatal infections have been reported in premature infants given probiotics, and the FDA has warned health care providers. [5] People with weak immune systems or serious illness should talk with their clinician before using probiotic products.
- No source we read shows that stool or microbiome tests sold to the public can guide aging decisions. See microbiome tests sold in integrative practice.
- The microbiome is one of twelve proposed hallmarks of aging, listed as "dysbiosis". [7] A hallmark is a framework for research, not a treatment target. See the hallmarks of aging.
For basic digestive biology see how digestion and the microbiome work, and for the animal-to-human gap see aging in animals vs humans.
References
- Claesson MJ et al. Gut microbiota composition correlates with diet and health in the elderly. Nature, 2012. Read 2026-10-22.
- Gut microbiome and healthy ageing: a systematic review of literature. Microbiology (Reading), 2026. Read 2026-10-22.
- Ghosh TS et al. Mediterranean diet intervention alters the gut microbiome in older people reducing frailty and improving health status: the NU-AGE 1-year dietary intervention across five European countries. Gut, 2020. Read 2026-10-22.
- Gut microbiome modulation can improve cognitive function in older adults: a systematic review and meta-analysis. Age and Ageing, 2026. Read 2026-10-22.
- NCCIH, Probiotics: What You Need To Know. Page last updated August 2019. Read 2026-10-22.
- Life-long microbiome rejuvenation improves intestinal barrier function and inflammaging in mice. Microbiome, 2025. Read 2026-10-22.
- López-Otín C et al. Hallmarks of aging: An expanding universe. Cell, 2023. Read 2026-10-22.