# Efficacy of probiotic and synbiotic supplementation on the length of hospital stays and risk of postoperative mortality in patients undergoing surgery: an umbrella review of systematic reviews and meta-analyses of randomized clinical trials

## TL;DR

This study finds that probiotics and synbiotics can reduce hospital stays for surgery patients, but the evidence quality is mixed.

## Contribution

This is the first umbrella review to systematically evaluate the certainty of evidence on probiotic and synbiotic effects on hospital stay and mortality in surgical patients.

## Key findings

- Probiotic supplementation reduced hospital stay by 1.00 day in surgical patients.
- Synbiotic supplementation reduced hospital stay by 2.57 days, more than probiotics.
- Neither probiotics nor synbiotics significantly affected ICU stay or postoperative mortality.

## Abstract

This umbrella review was conducted to assess the certainty and validity of all available meta-analyses for intervention trials regarding the impact of synbiotic and probiotic interventions in hospital and Intensive Care Unit (ICU) stay durations, as well as postoperative mortality risk among patients undergoing surgery.

A comprehensive systematic search was performed by applying Web of Science, Scopus, PubMed, Embase and Cochrane Library until July 20, 2025. Meta-analyses were used to evaluate the effect of synbiotic and probiotic interventions among hospital and ICU stay durations, as well as the postoperative mortality risk in patients undergoing surgery. Effect sizes of synbiotic and probiotic interventions were recalculated by using a random effects model, and the GRADE tool was used to determine evidence certainty.

Forty-eight clinical trials involving 6,378 participants (intervention = 3151; placebo = 3227) across thirty meta-analyses were included in this study. The findings indicated that probiotic supplementation (vs. placebo) significantly reduced the duration of hospital stay [Weighted Mean Difference (WMD): –1.00 days; 95% CI: –1.37 to –0.64; I2 = 63.1%; moderate certainty of evidence; P < 0.001; n = 22] among patients undergoing surgery. Synbiotic supplementation showed even greater efficacy, reducing the length of hospital stay by a larger margin (WMD: –2.57 days; 95% CI: –4.51 to –0.64; I2 = 83.2%; moderate certainty of evidence; P = 0.009; n = 19). Moreover, the results suggested that synbiotic supplementation did not affect the length of ICU stay. The results indicated that the risk of postoperative mortality did not significantly change after probiotic or synbiotic supplementation (vs. placebo) among patients undergoing surgery.

The current review supports the efficacy of synbiotic and probiotic supplementation on decreasing the length of hospital stay in patients undergoing surgery. However, it is important to note that 42.3% of included systematic reviews and meta-analyses (SRMAs) were rated as 'critically low' quality using the AMSTAR2 tool, which necessitates cautious interpretation of findings.

The online version contains supplementary material available at 10.1186/s40001-025-03756-0.