Dysbiosis

What it is

The gut microbiome — trillions of microorganisms in the lower gastrointestinal tract — shifts in composition and function with age. Diversity tends to fall, beneficial short-chain-fatty-acid producers decrease, and pro-inflammatory species expand. The result is changes in nutrient handling, bile-acid signalling, immune education, and even the metabolites that cross to the brain.

Why it matters in aging

Microbiome composition correlates with frailty, cognitive function, immune status, and response to many drugs (including immunotherapies). Centenarian microbiomes share distinctive features (e.g. enriched Akkermansia, Christensenellaceae) across populations.

Mechanisms

• SCFA production (acetate, propionate, butyrate) regulates colonic epithelial health and systemic inflammation.
• Bile-acid transformations modulate FXR and TGR5 signalling.
• TMAO from choline/carnitine metabolism associates with cardiovascular risk.
• Gut barrier integrity declines; LPS translocation feeds inflammaging.

What’s being studied

Mediterranean diet, fibre-rich and fermented-food interventions, and (cautiously) faecal microbiota transplantation in frailty trials. Akkermansia muciniphila supplementation is an active area. Generic over-the-counter probiotics have weak evidence for healthspan endpoints.

Related entries

See also: Chronic inflammation, Mediterranean diet.