<p><b>AIM</b></p><p>To investigate effects of host- and gut microbiota (GM)-altering interventions on sarcopenia (parameters).</p><p><b>METHODS</b></p><p>Upon PROSPERO registration (CRD42022347363), six databases and one registry were searched until January 5th 2024 and updated on June 10th 2025 for diet, pre-, pro-, or synbiotics mono-interventions in populations with mean age ≥ 50 years. (Standardized) mean differences (SMD) and 95% confidence intervals (CI) were computed using random-effects models if heterogeneity was > 50%. Risk of bias (Rob) & GRADE assessments were carried out to assess the evidence' quality and certainty.</p><p><b>RESULTS</b></p><p>The qualitative analysis included 38 diet, 13 prebiotics, 11 probiotics and 1 synbiotics studies, totaling 4842 participants (59%♀), mostly of high RoB.

The quantitative analysis included 49 studies. Probiotics improved muscle strength by 1.90 kg and gait speed by 0.08 m/s.

Fiber (whole-food)-enriched diets improved muscle strength with 1.25 kg and energy-restricted diets, aimed at weight loss, improved muscle mass if mean age was < 60 years and if the intervention lasted no longer than 12 weeks. High-protein diets improved muscle mass in women and if the intervention lasted at least 12 weeks.

Studies involving participants with sarcopenia were only included in the qualitative analysis, since none provided sufficient data to allow a quantitative synthesis.</p><p><b>DISCUSSION</b></p><p>Fiber (whole food)-enriched diets and probiotics improve muscle strength. The latter intervention also improves gait speed.

High-protein diets improve muscle mass in women and with intervention durations ≥ 12 weeks. Future studies should include fecal sampling to assess whether GM modulate the observed effects.</p><p><b>CONCLUSION</b></p><p>Specific diets and probiotics offer potential to improve sarcopenia parameters.</p>