Can you see how fast you are ageing from your stool?
Your microbiome does change with age and is associated with health risks, but a reliable ageing test based on stool does not yet exist for routine clinical use.
The gut microbiome changes measurably with age. A systematic review of 27 studies shows that the composition of gut bacteria differs between young adults, younger older adults, and the very oldest elderly (80+). Some bacterial species increase at older ages, while others decline. All studies were snapshots in time, so cause and effect have not been established.
Based on 55 age-related bacterial species found in stool, researchers calculated a so-called 'microbiome age': a number indicating how 'old' your gut flora looks compared with your calendar age. This model was validated in more than 4,400 people. In metabolically unhealthy people aged 60 and over, such as those with obesity or high blood sugar, a higher microbiome age was linked to an up to 117% greater risk of cardiovascular disease. However, this is an association: there is as yet no evidence that actively adjusting your microbiome also reduces the risk.
There is also mechanistic research showing how gut bacteria influence ageing. A particular gut bacterium (Clostridium sp.) produces increasing amounts of phenylacetic acid as we age, a substance that accelerates vascular disease. In mouse studies, this sped up the ageing of blood vessels. At the same time, acetate, a protective substance produced by other gut bacteria, decreases with age. Whether these insights can be translated into treatments in humans remains unknown.
Stool analysis also has diagnostic potential. A meta-analysis of 8 studies identified 29 bacterial species that are consistently elevated in colorectal cancer; the researchers involved have commercial interests, which should be taken into account. In addition, research in nearly 800 cancer patients shows that microbiome patterns can predict who will benefit from immunotherapy. Abnormal patterns have also been found in Parkinson's disease, but those findings partly contradict one another and it is unclear what is cause and what is effect.
In short: stool analysis is not a mature ageing test you can do at home. There are promising associations, but clinically validated tests based on the microbiome do not yet exist for everyday use.
Based on a systematic review (27 studies), a large Chinese cohort study (>10,000 participants + validation in 4,425 samples), Swiss mechanistic research (human + mouse), a meta-analysis for colorectal cancer diagnostics (768 patients, with reported commercial interests), and two systematic reviews/meta-analyses for immunotherapy (808 patients) and Parkinson's disease (26 studies) respectively. All studies are associative in nature, except for the mechanistic animal research (likely_causal).
Can your microbiome reveal how old you are biologically?
Your microbiome does send signals about how you are ageing, but a reliable clinical test to measure your biological age with it does not yet exist. It certainly makes sense to take your gut health seriously, even if it is still too early to know how best to do so in order to slow ageing.
Can certain fungi or bacteria in your gut influence your cellular ageing?
Certain gut bacteria produce substances that accelerate cellular ageing, while a diverse microbiome rich in fibre-fermenting bacteria is actually protective. You can already take this into account through a high-fibre diet, but direct interventions in humans have barely been studied.
Does my gut microbiome change as I get older, and does it matter?
Your gut microbiome certainly changes as you get older, but whether that is harmful depends strongly on which direction that change goes. What you eat has a major influence on this, so that is a concrete area to pay attention to.
Can your gut microbiome influence how long you live?
There are clear indications that the composition of your gut microbiome is associated with how long and how healthily you age, but whether modifying your microbiome extends your life has not yet been demonstrated in humans.
Can your gut microbiome influence inflammation in your body?
Your gut microbiome can influence inflammatory processes throughout your body via the gut wall. Eating more fibre and exercising regularly are the most well-supported ways to influence this favourably.
Can your gut microbiome control your appetite and hunger?
Yes, your gut microbiome can influence your hunger and eating behaviour via a direct connection to your brain. Eating more fibre is the best thing you can do right now to support that route.