Can your microbiome reveal how old you are biologically?
Your gut microbiome demonstrably changes with the years and is associated with healthy ageing, but as a biological age marker it is currently too unreliable to draw practical conclusions from. What you eat carries at least as much weight as your age; it is therefore better to focus on a diverse, fibre-rich diet than on microbiome testing.
The bacteria in your gut shift gradually throughout your entire life. There is no clear tipping point, but the cumulative changes have been repeatedly demonstrated in studies conducted worldwide. For example, the bacterium Akkermansia (linked to a healthy gut wall) becomes relatively more abundant in older adults, while bacteria such as Faecalibacterium and Lachnospiraceae actually decline.
Researchers are building 'ageing clocks' based on the composition of your gut microbiome: models that try to predict how biologically old you are. That field is growing, but is still very much in development. The microbiome can also indirectly influence the epigenetic ageing of your cells through small molecules (metabolites), although this mechanism has not yet been well established in humans.
One surprising finding: in the very oldest individuals, people in their eighties and nineties, the diversity of bacterial species in the gut is sometimes actually higher than in people aged sixty to seventy. A diverse gut microbiome containing bacteria that produce anti-inflammatory substances (such as butyrate) has been linked to healthy ageing in multiple countries. At the same time, in most people as they age, microbial diversity gradually declines, and a disrupted microbiome can contribute to the smouldering chronic inflammation that characterises ageing.
There is an important practical nuance: your diet and living situation, such as residing in a care home for an extended period, are at least as influential on your microbiome composition as your age itself. This makes it difficult to say whether a microbiome reflects something about your biological age, or simply about what you have been eating for years. Combinations with other biological measures, such as DNA methylation or lipid profiles, appear more promising for distinguishing biological from chronological age, but those are still in development as well.
Claims are based on multiple observational studies and a systematic review (27 human studies). No RCTs or interventions are involved. All associations are correlational; causality has not been proven, except for the inflammaging mechanism (likely causal). Ageing clocks based on the microbiome are in development but have not yet been clinically validated.