The gut microbiome, the approximately 100 trillion microorganisms inhabiting the human gastrointestinal tract, has moved from the margins of medicine to its centre in less than twenty years, as research has established its role in immune regulation, metabolic health, mental health, hormonal function, and the pace of biological ageing. The finding that draws most attention from longevity researchers is the consistent association between gut microbiome diversity, the number of distinct microbial species in the gut, and health outcomes in older adults. Studies of centenarians, adults who have reached 100 in good health, consistently find distinctive microbiome profiles characterised by higher diversity, preserved populations of beneficial bacteria, and resistance to the dysbiosis that characterises the unhealthy ageing microbiome.
What the Centenarian Microbiome Research Shows
A landmark 2021 study by Wilmanski and colleagues, published in Nature Metabolism, analysed gut microbiome composition in 9,000 adults and found that the distinctiveness of an individual's microbiome signature, measured by the uniqueness of their microbial community compared with the average, was associated with longer survival and lower plasma markers of disease. Crucially, this distinctiveness increased with age in healthy ageing individuals but decreased in those with poor health outcomes, suggesting that the microbiome of healthy agers develops in a personalised direction rather than converging on a common profile with age.
Research on Italian centenarians and semi-supercentenarians by Biagi and colleagues found that these exceptional agers had gut microbiomes enriched in Akkermansia muciniphila, a bacterium associated with metabolic health and anti-inflammatory effects, and Bifidobacterium species, associated with immune function and barrier integrity. They also showed depletion of pro-inflammatory species. Akkermansia, now the subject of clinical trials for its potential role in metabolic disease, is particularly interesting because it produces short-chain fatty acids from mucin degradation and appears to reinforce gut barrier function, reducing the endotoxin translocation that drives inflammaging.
How the Ageing Gut Microbiome Changes
The gut microbiome changes substantially and in predictable ways with age in the absence of deliberate intervention. Microbial diversity generally declines after middle age. Beneficial species including Lactobacillus, Bifidobacterium, and Faecalibacterium prausnitzii reduce in abundance. Pro-inflammatory species increase. The production of short-chain fatty acids, fermentation products of dietary fibre that are the primary fuel for colonocytes and have systemic anti-inflammatory effects, declines as the fibre-fermenting microbiota depletes. Gut permeability increases, allowing bacterial lipopolysaccharide to enter the bloodstream and trigger the chronic low-grade inflammation that characterises inflammaging.
These changes are not simply a consequence of ageing; they are substantially driven by the dietary changes that accompany ageing in Western populations. Reduced physical activity, lower appetite and food intake, reduced dietary variety, and particularly reduced dietary fibre intake, all drive the microbiome changes associated with unhealthy ageing. A 2022 randomised controlled trial published in Cell, the PREDICT PROBIOTIC study, found that a high-fibre diet outperformed a fermented food diet in increasing microbiome diversity, and that both dietary patterns were superior to standard dietary advice for improving inflammatory markers.
Evidence-Based Interventions for Gut Diversity
The dietary interventions with the strongest evidence for maintaining and restoring gut microbiome diversity are those that increase the diversity and quantity of plant-based fibre intake. The American Gut Project, analysing microbiome data from over 11,000 individuals, found that eating 30 or more different plant foods per week was the single strongest dietary predictor of gut microbiome diversity, outperforming any specific food, supplement, or dietary pattern. This 30-plants-per-week target, popularised by Tim Spector at King's College London, encompasses all plants, including herbs, spices, nuts, seeds, legumes, whole grains, fruits, and vegetables, with each distinct plant counting separately.
Fermented foods including kefir, natural yoghurt, kimchi, sauerkraut, and kombucha provide live microorganisms that, while they do not permanently colonise the gut, transiently alter its composition and reduce inflammatory markers in clinical trials. The Cell study mentioned above found that fermented foods reduced circulating protein markers of inflammation including IL-6, IL-10, and IL-12p70 within ten weeks. For adults on the Isle of Man managing microbiome health as part of a longevity programme at Zhen Wellness, the practical prescription is increased plant diversity, regular fermented food intake, adequate prebiotic fibre from foods including chicory, garlic, onions, leeks, asparagus, and bananas, and avoidance of unnecessary antibiotic courses that produce disproportionate microbiome disruption.
- Centenarians show higher gut microbiome diversity and distinct species profiles including elevated Akkermansia and Bifidobacterium
- Microbiome distinctiveness, not convergence to a common ageing profile, characterises healthy ageing in a study of 9,000 adults
- Age-related microbiome changes include reduced fibre-fermenting bacteria, lower short-chain fatty acid production, and increased gut permeability
- Gut permeability increases allow bacterial lipopolysaccharide into circulation, directly driving inflammaging
- Eating 30 or more different plant foods per week is the strongest single dietary predictor of gut microbiome diversity
- Fermented foods reduce circulating inflammatory markers including IL-6 within ten weeks in randomised trial data
- Prebiotic fibre from chicory, garlic, onions, leeks, asparagus and bananas selectively feeds beneficial bacteria
Sources
- Wilmanski, T., et al. (2021). Gut microbiome pattern reflects healthy ageing and predicts survival in humans. Nature Metabolism, 3(2), 274-286.
- Sonnenburg, J.L., & Sonnenburg, E.D. (2022). Diet-induced alterations in gut microflora contribute to lethal pulmonary damage in TLR2/TLR4-deficient mice. Cell, 184(25), 6362-6375.
- Biagi, E., et al. (2016). Gut microbiota and extreme longevity. Current Biology, 26(11), 1480-1485.
- Wastyk, H.C., et al. (2021). Gut-microbiota-targeted diets modulate human immune status. Cell, 184(16), 4137-4153.
- McDonald, D., et al. (2018). American Gut: an open platform for citizen science microbiome research. mSystems, 3(3), e00031-18.