Ageing is accompanied by physiological and lifestyle changes that may influence gut microbial metabolism. Short-chain fatty acids (SCFAs), including acetate, propionate, and butyrate, are microbial metabolites derived from dietary fibre fermentation and play important roles in host metabolic and immune function. This systematic review and meta-analysis examined age-related differences in faecal SCFA concentrations among apparently healthy adults. Following PRISMA guidelines, searches across five databases (MEDLINE, Embase, Cochrane Central, Scopus, and PubMed) identified 18 eligible studies comparing faecal SCFA levels between stratified age groups. Random-effects meta-analyses showed that older adults had lower faecal concentrations of acetate (standardised mean difference SMD −0.53, 95% CI −0.90 to −0.16; p = 0.005), propionate (SMD −0.32, 95% CI −0.53 to −0.12; p = 0.002), butyrate (SMD −0.25, 95% CI −0.44 to −0.05; p = 0.015), and total SCFAs (SMD −0.59, 95% CI −0.98 to −0.21; p = 0.003) compared with younger adults. Insufficient reporting of dietary intake and physical activity precluded reliable meta-regression analyses to determine the contribution of these lifestyle factors to between-study heterogeneity. However, meta-regression identified methodological factors, specifically immediate post-collection freezing of faecal samples, exclusion of participants using antibiotics and the geographic region of studies, as significant sources of heterogeneity. Collectively, these meta-analyses provide quantitative evidence that ageing is associated with reduced faecal SCFA concentrations, indicating a potential age-related decline in microbial fermentation capacity. Understanding whether this decline is a modifiable feature of healthy ageing warrants investigation in future longitudinal and interventional studies. • Ageing reduces faecal acetate, propionate, and butyrate levels • Large heterogeneity identified but not explained by age differences alone • Faecal sample freezing and antibiotic exclusion identified heterogeneity sources • Findings support reduced gut microbial fermentation as a hallmark of ageing
Alqarni et al. (2026) studied this question.