Table 2 Age-related changes in gut microbiota composition

Reduced Bifidobacterium

Decline in dietary fiber intake, increased oxidative stress

Decreased production of short-chain fatty acids (SCFAs), impaired gut barrier integrity

[66, 67, 71]

Increased Proteobacteria

Low-grade inflammation (inflammageing), immune surveillance decline

Enhanced pathobiont colonization, systemic inflammation

[65, 68, 76]

Enrichment of Pathobionts (e.g., Enterobacteriaceae)

Impaired immune regulation, changes in gut mucosal niche

Increased susceptibility to infections, gut dysbiosis

[66, 68, 81]

Reduced diversity of microbial species

Reduced mucus secretion, slower intestinal transit, dietary simplification

Weakened resilience against environmental stressors, impaired immune function

[69, 70, 74]

Altered Firmicutes/Bacteroidetes ratio

Changes in epithelial barrier integrity, chronic inflammation

Dysregulated immune responses, reduced SCFA production

[66, 69, 75]

Depletion of Clostridiales

Reduced dietary fiber fermentation, increased oxidative stress

Impaired Treg induction, increased inflammation

[67, 71, 79]

Reduction in SCFA-producing bacteria (e.g., Faecalibacterium prausnitzii)

Reduced metabolic cross-talk between gut and host

Weakened anti-inflammatory responses, enhanced leaky gut syndrome

[70, 74, 77]

Decreased Akkermansia muciniphila

Reduced mucin production, impaired intestinal epithelial repair

Increased intestinal permeability, systemic inflammation

[71, 78, 81]

Reduction in commensal bacteria (e.g., Lactobacillus)

Chronic inflammation, reduced immune surveillance

Reduced gut homeostasis, enhanced vulnerability to gut pathogens

[66, 67, 82]