The Gut-Longevity Connection: Microbiome and Ageing

Medically reviewed and written by Dr Zeeshan Afzal, MBBS — Medical Officer at Welzo. Last updated: 27 July 2026. Reading time: approximately 14 minutes.

The relationship between gut health and ageing is one of the most active areas in longevity science — and it is the natural next step after our foundational guide to gut health in the UK and our practical guide to gut health in older adults. Your gut microbiome — the trillions of bacteria, fungi, viruses and archaea living in your digestive tract — does not stay still across a lifetime. It shifts in composition, function and stability as you get older, and the direction of that shift now appears to track closely with how well you age, not simply how long you live. Browse the full Welzo gut health range and our probiotic supplements for the products referenced throughout this article, including Akkermansia, citrus pectin powder, Welzo Ultra Purity Berberine and Welzo Ultra Purity TUDCA.

In 2023, an updated version of the landmark "hallmarks of ageing" framework formally added dysbiosis — disruption of the microbiome — to the list of core biological drivers of ageing, alongside genomic instability, cellular senescence and chronic inflammation. That was a significant moment: gut health moved from a wellness talking point to a recognised pillar of ageing biology, sitting alongside microbiome diversity, gut barrier function and short-chain fatty acid production as measurable markers of how the body is ageing.

This guide explains what actually happens to the gut as you age, what the human evidence does and does not show, and the practical, evidence-based steps you can take from your forties onwards — from increasing fibre and eating 30 plants a week to choosing the best probiotics in the UK for your situation. Everything here is referenced to peer-reviewed research, NHS guidance or UK statistical bodies.

Start here: related Welzo guides

• Gut health in the UK: the complete guide — the pillar article for this cluster
• Gut health in older adults — symptoms and management after 65
• Microbiome diversity and how to increase gut bacteria diversity
• The gut–brain connection and gut health and the immune system
• How to choose a probiotic and the best prebiotic supplements in the UK
• The gut reset protocol — the structured version of the 8-week plan below

Key takeaways

• Microbiome composition begins drifting in mid-to-late adulthood — from roughly age 40–50 — long before most people notice any digestive change.
• In healthy older adults, the microbiome becomes increasingly unique to the individual. In less healthy older adults, that drift is absent. This "uniqueness signature" has been associated with survival in adults aged 78–98.
• Loss of fibre-fermenting, butyrate-producing bacteria is a consistent feature of unhealthy ageing and is linked to frailty and inflammation.
• Diet is the strongest modifiable lever. A 12-month Mediterranean-style diet trial in 612 older adults across five European countries shifted the microbiome and was associated with reduced frailty markers and lower inflammation.
• Most UK adults eat around 20g of fibre a day against a 30g target — closing that gap is the single highest-value change for most people.
• Supplements can support, but not replace, dietary and lifestyle change. Always check interactions with prescribed medicines.

Table of contents

• Why gut health and ageing are biologically linked
• What actually changes in the gut microbiome as you age
• Inflammaging: the inflammation–gut barrier connection
• The key human studies, summarised
• How digestion itself changes after 50
• Gut health and the systems that age fastest
• Evidence-based ways to support gut health as you age
• Supplements worth considering after 50
• A practical 8-week plan
• Testing and monitoring your gut as you age
• Red flags: when to see your GP
• Five myths about gut health and ageing
• Frequently asked questions
• References

Why gut health and ageing are biologically linked

The UK population is ageing rapidly. In 2022 there were around 12.7 million people aged 65 or over in the UK, making up 19% of the population; official projections suggest this could reach 22.1 million people, or 27%, by 2072. The central public health challenge is no longer lifespan alone but healthspan — the years lived in good function, free of disabling disease.

Ageing is a biological process, not just a number

Two people of the same chronological age can have very different biological ages. The rate at which tissues lose function is shaped by inflammation, immune competence, nutrient status, muscle mass and metabolic control — and the gut microbiome influences every one of those.

The gut is the largest immune interface in the body, the site where dietary fibre is converted into signalling molecules, and a major producer of neurotransmitter precursors. When that ecosystem degrades, the downstream effects are systemic rather than purely digestive.

Dysbiosis is now a formal hallmark of ageing

The 2023 update of the hallmarks of ageing framework expanded the original nine hallmarks to twelve, adding disabled macroautophagy, chronic inflammation and dysbiosis. This reflects a decade of accumulated evidence that age-associated microbiome disturbance is not just a passive marker of poor health but a plausible contributor to it.

Read more on what dysbiosis means in practice in our detailed article on gut dysbiosis and on microbiome diversity.

What "healthy ageing" looks like in gut terms

Researchers have moved away from the idea that there is one ideal "young" microbiome to preserve. Instead, healthy ageing appears to be characterised by a microbiome that continues to adapt — retaining fibre-fermenting capacity and metabolic output — rather than one that stalls in a generic, low-diversity state.

Diagram of the human digestive system. Image: Mariana Ruiz (LadyofHats), public domain, via Wikimedia Commons.

What actually changes in the gut microbiome as you age

The lifelong arc: infancy, stability, later-life flux

Microbiome change with age is best understood as a continuation of a lifelong succession that begins at birth. Infancy is a period of rapid assembly. Late childhood through middle age is typically a period of relative stability, unless disrupted by illness, antibiotics or major dietary change. The microbiome then enters a period of flux again in later life.

Antibiotics are a particularly important disruptor in older adults, who are prescribed them more frequently. If you have recently completed a course, see our guidance on taking probiotics after antibiotics.

Loss of diversity — and why context matters

The ELDERMET study, published in Nature in 2012, profiled the faecal microbiota of 178 older adults in Ireland. It found that microbiota composition clustered by residence setting — community, day hospital, rehabilitation or long-term residential care — and that clustering by diet separated people in the same way. People in long-stay care had significantly less diverse microbiota than community dwellers, and loss of the community-associated microbiota pattern correlated with increased frailty.

The crucial nuance is that the driver was diet, not age itself. Institutional diets tend to be lower in fibre variety, and the microbiome followed.

The "uniqueness signature" in healthy ageing

A 2021 Nature Metabolism study analysed gut microbiome, phenotypic and clinical data from more than 9,000 people aged 18 to 101 across three independent cohorts. Starting in mid-to-late adulthood, gut microbiomes became increasingly unique to each individual. This uniqueness was strongly associated with microbially produced amino acid derivatives circulating in the bloodstream.

In participants over roughly 80 years old, healthy individuals showed continued drift towards a unique compositional state, whereas this drift was absent in less healthy individuals. The pattern was characterised by depletion of core genera found in most humans, primarily Bacteroides. Retaining high Bacteroides dominance into older age, or having low microbiome uniqueness, predicted decreased survival over a four-year follow-up in a cohort of community-dwelling men aged 78–98.

The genus-level drift was reported to begin between roughly 40 and 50 years of age — which is why gut-focused interventions in midlife may matter more than interventions started at 75.

Fewer fibre fermenters, more opportunists

Across studies, a recurring pattern in less healthy older adults is a reduction in bacteria that ferment dietary fibre into short-chain fatty acids, alongside relative expansion of opportunistic organisms. This shift reduces the gut's output of beneficial metabolites at precisely the point in life when the body is least able to compensate.

Why butyrate matters more with age

Butyrate is the primary fuel source for colonocytes — the cells lining your colon. It supports tight junction integrity, has anti-inflammatory signalling effects, and helps regulate immune tone in the gut wall. When butyrate production falls, the barrier that separates gut contents from your bloodstream becomes less well maintained.

We cover this in depth in our guides to short-chain fatty acids, gut barrier function and butyrate supplements in the UK.

Inflammaging: the inflammation–gut barrier connection

"Inflammaging" describes the low-grade, chronic, sterile inflammation that accumulates with age. It is now listed among the twelve hallmarks of ageing, and it is mechanistically linked to cardiovascular disease, type 2 diabetes, neurodegeneration, sarcopenia and frailty.

Gut barrier decline

The intestinal barrier is a single cell layer with a protective mucus coat above it. With reduced butyrate supply, thinning mucus and altered mucin turnover, the barrier becomes more permeable to bacterial components such as lipopolysaccharide. When these fragments reach systemic circulation, they trigger innate immune activation — a plausible contributor to the inflammatory background noise of ageing.

For a balanced look at the science and its limits, see is leaky gut real? and the best supplements for leaky gut in the UK.

Immunosenescence

Immune ageing runs in parallel. Thymic involution reduces naive T-cell output, vaccine responses weaken, and infection resilience declines. Because a large proportion of immune tissue sits along the gut, microbiome quality plausibly influences how well that system holds up. Our article on the gut health and immune system connection covers the mechanisms in more detail, as does our piece on gut health and autoimmunity.

The key human studies, summarised

Study	Design	Main finding	Strength of evidence
Claesson et al., Nature, 2012 (ELDERMET)	178 older adults, observational	Diet-driven microbiota differences tracked with frailty, inflammation and residential setting	Observational; strong hypothesis-generating data
Ghosh et al., Gut, 2020 (NU-AGE)	612 non-frail/pre-frail adults, five countries, 12-month dietary intervention	Mediterranean diet adherence altered the microbiome; enriched taxa associated with lower frailty, better cognitive scores and lower inflammatory markers	Interventional; one of the largest dietary trials in older adults
Wilmanski et al., Nature Metabolism, 2021	>9,000 people, three cohorts, four-year survival follow-up in the oldest group	Microbiome uniqueness increases in healthy ageing; low uniqueness and high Bacteroides predicted reduced survival	Large observational cohorts; association, not proof of causation
Bárcena et al., Nature Medicine, 2019	Progeroid mouse models; faecal transplant and single-strain intervention	Transplant from healthy mice extended healthspan and lifespan; Akkermansia muciniphila alone was sufficient for benefit	Animal model — mechanistically important, not directly transferable to humans
López-Otín et al., Cell, 2023	Framework review	Dysbiosis and chronic inflammation added as formal hallmarks of ageing	Expert synthesis of the field

How to read this evidence honestly

Most human data on gut health and ageing is observational. It shows that microbiome patterns travel with health outcomes; it does not prove that changing the microbiome changes the outcome. The strongest interventional signal comes from whole-diet trials such as NU-AGE, not from single supplements. Animal work — including the striking progeria transplant experiments — establishes plausible mechanism but should not be presented as a human lifespan result. Anyone claiming a supplement extends human lifespan is going beyond the evidence.

For a critical look at the supplement evidence base, see do probiotics actually work?

How digestion itself changes after 50

Alongside microbiome shifts, the mechanics of digestion change with age. These changes are common, often manageable, and frequently mistaken for "just getting older".

Slower transit and constipation

Colonic transit tends to slow, pelvic floor coordination can weaken, physical activity often falls, and many commonly prescribed medicines slow the bowel further. Constipation becomes markedly more common in later life and is a frequent reason for reduced quality of life and hospital presentation.

Practical guidance is in our articles on constipation relief in the UK, magnesium for constipation and gut health in older adults.

Lower stomach acid and nutrient absorption

Gastric acid output can decline with age and is markedly reduced by long-term acid-suppressing medication. Stomach acid is needed to liberate vitamin B12 from food protein and to support absorption of iron, calcium and magnesium. Reduced acidity also weakens one of the body's defences against ingested organisms.

Relevant reading: low stomach acid symptoms, betaine HCl in the UK, digestive bitters and the long-term effects of omeprazole. Never stop a prescribed acid-suppressing medicine without speaking to your GP.

Polypharmacy: the underrated microbiome factor

Older adults typically take more prescribed medicines, and many of them influence the gut — proton pump inhibitors, metformin, antibiotics, opioid analgesics, iron supplements, antidepressants and non-steroidal anti-inflammatories among them. Medication effects can rival diet as a driver of microbiome change in later life.

See our guides to metformin stomach side effects, ibuprofen and stomach damage, iron supplements and constipation and antidepressants and constipation.

Appetite, protein intake and muscle

Appetite tends to fall with age while protein requirements per kilogram arguably rise. Reduced intake of varied plant foods narrows fibre diversity, which in turn narrows microbial diversity — a loop that accelerates in people who are unwell, isolated or in institutional care, as ELDERMET illustrated.

Gut health and the systems that age fastest

Brain and cognition

The gut–brain axis operates through vagal signalling, immune mediators and microbial metabolites. In the NU-AGE trial, taxa enriched by Mediterranean diet adherence were positively associated with markers of improved cognitive function and negatively associated with inflammatory markers including C-reactive protein. This is an association within a dietary trial, not proof that bacteria improve memory — but it is one of the better-quality human signals available.

Explore further in the gut–brain connection, the vagus nerve and the gut and probiotics for anxiety.

Muscle, bone and frailty

Frailty is the outcome most consistently linked to microbiome pattern in ageing research. Both ELDERMET and NU-AGE reported associations between microbiota composition and frailty measures. The plausible mechanisms include inflammation-driven muscle catabolism, altered amino acid availability and reduced nutrient absorption.

Metabolic health and blood sugar

Fibre fermentation influences post-meal glucose responses, insulin sensitivity and lipid handling. As metabolic tolerance narrows with age, these effects become more consequential. See gut health and blood sugar and fibre and cholesterol.

Skin, hormones and sleep

Age-related changes in gut function also intersect with skin barrier health, hormonal transitions and sleep quality. Our related guides cover gut health and skin, gut health and hormones, gut health in menopause and gut health and sleep.

Evidence-based ways to support gut health as you age

The interventions with the best human evidence are dietary and behavioural. Supplements are a supporting layer, not a substitute.

The Mediterranean dietary pattern used in the NU-AGE trial emphasises plants, pulses, wholegrains, olive oil and fish. Image via Wikimedia Commons.

1. Close the fibre gap

UK government guidance is 30g of dietary fibre per day for adults, yet NHS figures indicate most adults consume only around 20g. Fibre is the raw material your microbiome ferments into short-chain fatty acids, so a fibre gap is, functionally, a metabolite gap.

Increase intake gradually over several weeks, and increase fluid alongside it. Moving too quickly commonly causes bloating and wind. Our step-by-step guides: how to increase fibre and high-fibre foods in the UK.

2. Aim for plant diversity, not just plant quantity

Different fibres feed different microbes. Counting distinct plant foods per week — vegetables, fruit, wholegrains, legumes, nuts, seeds, herbs and spices all count — is a practical way to widen the substrate range. See 30 plants a week and how to increase gut bacteria diversity.

3. Adopt a Mediterranean-style pattern

NU-AGE remains the most relevant intervention trial for this age group: 612 non-frail or pre-frail participants across the UK, France, the Netherlands, Italy and Poland followed a 12-month Mediterranean diet tailored to older adults. Adherence produced specific microbiome changes, and taxa enriched by the diet occupied keystone positions in microbial networks while frailty-associated taxa sat at the periphery.

See also the best foods for gut health, prebiotic foods, polyphenols and gut health and resistant starch.

Pulses are among the highest-fibre foods available in UK supermarkets. Image: public domain, via Wikimedia Commons.

4. Include fermented foods regularly

Live yoghurt, kefir, sauerkraut, kimchi and traditionally fermented cheeses introduce live organisms and fermentation by-products. They are not equivalent to a defined-strain probiotic, but they are a low-cost, food-first option that fits easily into most diets.

Compare the approaches in fermented food vs probiotics, fermented foods in the UK, kefir benefits and kefir vs probiotics.

Traditional fermentation vessels. Image via Wikimedia Commons.

5. Protect muscle with protein and resistance training

Muscle is the tissue most strongly associated with independence in later life. Spreading protein across meals and performing resistance exercise two to three times weekly supports muscle retention, and physical activity independently improves bowel transit. Our article on gut health in athletes covers exercise–gut interactions in more depth.

6. Reduce ultra-processed food and manage alcohol

Diets dominated by ultra-processed foods tend to be low in fibre and plant variety and high in emulsifiers and certain sweeteners. See ultra-processed food and the gut and sweeteners and gut health.

7. Sleep, stress and circadian rhythm

The gut has a circadian rhythm of its own. Irregular sleep, night eating and shift patterns disturb it. Our guides to shift work and digestion and gut health and sleep cover practical adjustments.

Supplements worth considering after 50

Supplements should be chosen for a specific, defined purpose and reviewed after 8–12 weeks. If you take prescribed medication, have kidney or liver disease, or are immunocompromised, speak to your GP or pharmacist before starting anything new.

Probiotics

Effects are strain-specific, not species-specific or generic. Choose products that state the exact strain, the guaranteed count at end of shelf life, and the evidence behind that strain. Browse the Welzo probiotics range, and read how to choose a probiotic, the best probiotics in the UK, when to take probiotics and probiotic safety.

Prebiotics and synbiotics

Prebiotics feed the bacteria you already have, which can be a more sensible starting point than adding new organisms. Start low: gas and bloating are common when doses escalate too quickly. See the best prebiotic supplements in the UK, prebiotic vs probiotic and synbiotic supplements.

Akkermansia muciniphila

Akkermansia is a mucin-associated organism that has attracted attention in ageing research. In progeroid mice, transplantation of A. muciniphila alone was sufficient to produce benefit, and centenarians have been reported to show higher levels of Verrucomicrobia, the phylum it belongs to. Human intervention data in ageing populations remains limited, so treat this as promising rather than proven.

See our Akkermansia supplement, plus Akkermansia vs conventional probiotics and pasteurised Akkermansia.

Modified citrus pectin

Pectin is a soluble fibre; modified citrus pectin is a lower-molecular-weight form that has been studied for reasons beyond fermentation. As a fibre source it contributes to the substrate pool your microbes rely on. See our citrus pectin powder and compare formats in modified citrus pectin vs standard pectin and psyllium vs inulin.

Berberine

Berberine is a plant alkaloid studied mainly for metabolic endpoints, and it also has antimicrobial activity that affects gut organisms. It interacts with several common medicines, including some statins and diabetes drugs, so medical advice first is essential. See Welzo Ultra Purity Berberine, berberine interactions and berberine vs metformin.

TUDCA and bile flow

Bile acids are microbially modified and act as signalling molecules. The 2019 progeria work pointed to restoration of secondary bile acids as one plausible mechanism behind the benefits of correcting dysbiosis. TUDCA is a bile acid derivative available as a supplement. See Welzo Ultra Purity TUDCA, TUDCA side effects, TUDCA vs milk thistle and bile acid malabsorption.

Barrier-support nutrients

Zinc carnosine, L-glutamine, collagen peptides and colostrum are commonly used for gut lining support. Evidence quality varies considerably by ingredient and indication. See zinc carnosine, glutamine vs collagen for the gut, collagen for gut health and the best colostrum in the UK.

Digestive enzymes

Enzyme supplements are appropriate for specific deficiencies rather than as a general anti-ageing measure. Lactase for diagnosed lactose intolerance is a clear example. See how to take digestive enzymes, enzymes vs probiotics and lactose intolerance supplements.

Safety notes specific to older adults

• Check every new supplement against your current prescription list with a pharmacist.
• People who are significantly immunocompromised, have central venous access, or are critically unwell should not start live probiotics without specialist advice.
• Introduce one product at a time so you can attribute any effect — or side effect — accurately.
• Review after 8–12 weeks. If nothing has changed, stop rather than accumulate products.
• Very high fibre supplement doses without adequate fluid can worsen constipation rather than relieve it.

A practical 8-week plan

Weeks	Focus	Actions
1–2	Baseline	Record current fibre intake and distinct plant foods per week. Note stool form using the Bristol scale. List all medicines and supplements.
3–4	Fibre and fluid	Add roughly 5g fibre per week towards 30g. Increase water. Add one pulse-based meal every other day.
5–6	Diversity and fermentation	Push plant variety towards 30 per week. Introduce one fermented food daily. Add resistance training twice weekly.
7–8	Targeted support	If symptoms persist, consider one targeted supplement. Reassess stool form, bloating, energy and regularity against your week 1 baseline.

A structured version of this approach is set out in our gut reset protocol.

Testing and monitoring your gut as you age

Track stool form first — it is free

The Bristol Stool Chart is the simplest validated tool for tracking bowel function over time, and it is more useful than most consumer tests for spotting a genuine change.

Bristol Stool Chart. Image: Cabot Health, CC BY-SA 3.0, via Wikimedia Commons. See our full guide to the Bristol Stool Chart.

Microbiome tests

Consumer microbiome sequencing can be interesting, but the science is not yet at the point where a report can tell you reliably which supplement you personally need. Treat results as a snapshot rather than a diagnosis. See gut microbiome tests in the UK and our microbiome test comparison.

Clinically meaningful tests

Tests with established clinical use include faecal calprotectin for inflammation, coeliac serology, H. pylori testing, and standard blood tests covering full blood count, ferritin, B12, folate and inflammatory markers. See calprotectin testing, coeliac testing, H. pylori testing and the gut health blood test.

Do not skip NHS bowel screening

NHS bowel cancer screening is offered by post to eligible age groups across the UK. Screening detects disease before symptoms appear and is a far higher-value use of attention than any supplement decision. See bowel cancer screening in the UK.

Red flags: when to see your GP

Do not attribute new digestive symptoms in later life to ageing. Contact your GP promptly if you notice:

• Blood in your stool, or black, tarry stools
• Unintentional weight loss
• A persistent change in bowel habit lasting three weeks or more
• Difficulty or pain when swallowing
• Persistent vomiting, or vomiting blood
• A new abdominal or rectal lump
• Unexplained iron deficiency anaemia
• Persistent abdominal pain, particularly if it wakes you at night
• New symptoms starting after age 50 without an obvious cause

Our guide on when to see a GP about stomach symptoms explains what to expect at the appointment.

Five myths about gut health and ageing

Myth 1: Everyone's microbiome inevitably deteriorates with age

The data suggest otherwise. Healthy older adults show continued adaptive change; it is the absence of that drift that tracks with poorer outcomes.

Myth 2: More probiotic strains and higher CFU counts are always better

Dose and strain count are marketing-friendly numbers, not measures of efficacy. What matters is whether the specific strain has been studied for your specific goal. See single vs multi-strain probiotics and CFU vs AFU.

Myth 3: Digestive symptoms are a normal part of getting older

Some functional changes are common with age, but persistent new symptoms warrant assessment rather than acceptance.

Myth 4: A faecal transplant can rejuvenate the human microbiome

Faecal microbiota transplantation is an established treatment for recurrent Clostridioides difficile infection. Its use as an anti-ageing intervention rests on animal data. See C. difficile and probiotics.

Myth 5: Supplements can replace diet

The strongest human intervention data in this field comes from whole-diet change, not capsules. Supplements are best used to fill a defined gap.

Frequently asked questions

At what age does the gut microbiome start to change?

Compositional drift towards a more individual microbiome profile has been reported to begin between roughly 40 and 50 years of age at the genus level, and slightly later at finer taxonomic resolution. Most people notice no symptoms at that stage, which is why midlife is a sensible point to start paying attention.

Does poor gut health actually shorten life expectancy?

Observational data in adults aged 78–98 found that low microbiome uniqueness and retained high Bacteroides dominance predicted decreased survival over four years of follow-up. That is an association within one cohort, not proof that the microbiome causes mortality. It does, however, place gut health among the measurable markers of ageing trajectory.

What is the single best thing I can do for my gut after 60?

Increase dietary fibre towards the 30g daily target using a wide variety of plant foods, introduced gradually with adequate fluid. It is the intervention with the broadest supporting evidence and the widest downstream benefit, including cardiovascular and bowel cancer risk.

Should older adults take a probiotic every day?

Daily use is reasonable if you have a specific goal and a strain chosen for it, and if you review the benefit after 8–12 weeks. It is not automatically necessary. Read should I take probiotics every day? and how long probiotics take to work.

Is Akkermansia the "longevity bacterium"?

It is one of the most interesting organisms in ageing research — single-strain administration produced benefit in progeroid mice, and centenarians have shown higher levels of its phylum. But human trials in ageing populations are limited, and calling it a longevity bacterium overstates current evidence.

Can improving gut health reduce inflammation?

In the NU-AGE trial, microbiome changes driven by Mediterranean diet adherence were negatively associated with inflammatory markers including C-reactive protein and interleukin-17. Diet-led improvement in gut function plausibly contributes to lower inflammatory burden, though isolating the microbiome's specific contribution remains difficult.

Why do I bloat more now than I did in my thirties?

Common contributors include slower transit, altered fermentation patterns, changes in medication, reduced physical activity, and abrupt increases in fibre. See supplements for bloating, foods that cause bloating and trapped wind relief. Persistent new bloating in older adults should always be discussed with a GP.

Do gut changes with age affect vitamin absorption?

Yes. Reduced gastric acid — from age or long-term acid-suppressing medication — impairs the release of vitamin B12 from food protein and can affect iron, calcium and magnesium absorption. B12 status is worth checking if you have been on a proton pump inhibitor long term.

Is a low FODMAP diet suitable for older adults?

It can help diagnosed IBS but is restrictive and reduces fibre variety, which is a real drawback in later life. It should be time-limited and supervised, with structured reintroduction. See the low FODMAP diet and FODMAP reintroduction.

How long before I notice a difference?

Bowel regularity often responds to fibre and fluid changes within one to two weeks. Microbiome composition shifts over weeks to months — the NU-AGE intervention ran for twelve months. Judge dietary changes over at least eight weeks rather than eight days.

References

1. López-Otín C, Blasco MA, Partridge L, Serrano M, Kroemer G. Hallmarks of aging: an expanding universe. Cell. 2023;186(2):243–278. Read the paper
2. Wilmanski T, Diener C, Rappaport N, et al. Gut microbiome pattern reflects healthy ageing and predicts survival in humans. Nature Metabolism. 2021;3(2):274–286. Read the paper | Full text (PMC)
3. National Institute on Aging. Unique gut microbiome patterns linked to healthy aging, increased longevity. NIA summary
4. Ghosh TS, Rampelli S, Jeffery IB, 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;69(7):1218–1228. PubMed record | DOI
5. Claesson MJ, Jeffery IB, Conde S, et al. Gut microbiota composition correlates with diet and health in the elderly. Nature. 2012;488(7410):178–184. Read the paper | PubMed record
6. Bárcena C, Valdés-Mas R, Mayoral P, et al. Healthspan and lifespan extension by fecal microbiota transplantation into progeroid mice. Nature Medicine. 2019;25:1234–1242. Read the paper | PubMed record
7. Ghosh TS, Shanahan F, O'Toole PW. The gut microbiome as a modulator of healthy ageing. Nature Reviews Gastroenterology & Hepatology. 2022;19:565–584. Read the review
8. O'Toole PW. Ageing, microbes and health. Microbial Biotechnology. 2024. Full text (PMC)
9. From dysbiosis to longevity: a narrative review into the gut microbiome's impact on aging. Journal of Biomedical Science. 2025. Read the review
10. NHS. How to get more fibre into your diet. NHS guidance
11. British Nutrition Foundation. Fibre. Nutrition information
12. House of Commons Library. The UK's changing population. Briefing
13. Office for National Statistics. Past and projected period and cohort life tables, 2022-based, UK. ONS bulletin
14. Centre for Ageing Better. The State of Ageing 2025: our ageing population. Report
15. British Heart Foundation. High fibre foods: how much fibre should you eat per day? Guidance

About the author

Dr Zeeshan Afzal, MBBS is a qualified medical doctor and Medical Officer at Welzo. He writes and medically reviews Welzo's digestive health and longevity content, with a focus on translating peer-reviewed evidence into practical guidance for UK patients.

Medical disclaimer

This article is for general information and education. It is not a substitute for individual medical advice, diagnosis or treatment. Do not delay seeking advice from your GP or another qualified healthcare professional because of something you have read here, and do not stop or change prescribed medication without medical advice. If you have concerning symptoms, contact your GP, call NHS 111, or in an emergency call 999. Supplements are not intended to diagnose, treat, cure or prevent any disease.

Continue reading

• Gut health in older adults
• Gut health in the UK: the complete guide
• Best probiotics in the UK
• 30 plants a week
• Shop gut health supplements