Impact of Bowel Preparation on Gut Microbiota

Bowel preparation, commonly employed prior to colonoscopy or colorectal surgery, exerts a pronounced yet largely transient disturbance on the human gut microbiota. Mechanical lavage with polyethylene glycol or osmotic agents, often combined with stimulant laxatives or enemas, leads to substantial reductions in microbial richness and evenness, particularly affecting obligate anaerobes within the Firmicutes and Bacteroidetes phyla. Metabolic outputs such as short-chain fatty acids decline in parallel, reflecting a temporary loss of fermentative activity. Most studies indicate that community structure and metabolite profiles recover within one to two weeks, although the trajectory of re-colonisation varies among individuals and preparation regimens. The timing of faecal sampling relative to preparation is critical: samples collected immediately post-prep may misrepresent steady-state ecology, whereas those obtained after the recovery phase better reflect baseline composition. In surgical settings, alterations in microbiota composition have been linked to postoperative infection risk and anastomotic leakage, prompting investigation of targeted probiotic or prebiotic interventions to accelerate microbial restoration. Standardising preparation protocols and integrating microbiome-friendly adjuvants could mitigate dysbiosis, optimise diagnostic yield, and enhance patient outcomes. A deeper understanding of how different preparation modalities impact mucosal-associated versus luminal communities will inform both clinical practice and the design of robust microbiome studies.

Research from Nature Portfolio

A foundational analysis demonstrated that standard bowel cleansing markedly reduces genera-level diversity and profoundly disrupts metabolite networks immediately after preparation. Using 16S rRNA sequencing and metabolomic profiling, researchers found significant declines in community complexity and short-chain fatty acid concentrations, with near-complete restoration by day 14. This work established critical guidelines for timing of faecal sampling and highlighted the resilience of the gut ecosystem, underscoring the importance of avoiding post-prep sampling when assessing baseline microbiome status.

Impact of Bowel Preparation on Gut Microbiota publication trend

The graph below shows the total number of articles in impact of bowel preparation on gut microbiota across all publications each year (not limited to Nature Index journals).

Technical terms

Bowel preparation: Administration of agents (e.g. polyethylene glycol, stimulant laxatives, enemas) to cleanse the colon prior to endoscopy or surgery.

Gut microbiota: The community of bacteria, archaea, fungi and viruses residing within the gastrointestinal tract.

Dysbiosis: A state of disrupted microbial balance characterised by loss of diversity or overrepresentation of opportunistic taxa.

16S rRNA sequencing: A molecular method that targets the 16S ribosomal RNA gene to profile bacterial community composition.

Short-chain fatty acids (SCFAs): Metabolic by-products (e.g. acetate, propionate, butyrate) produced by bacterial fermentation of dietary fibres, important for colonic health.

β-diversity: A metric of compositional dissimilarity between microbial communities across different samples or time points.

References

1. Gut microbiota dynamics and fecal SCFAs after colonoscopy: accelerating microbiome stabilization by Clostridium butyricum. Journal of Translational Medicine (2024).
2. Impact of mechanical bowel preparation on the gut microbiome of patients undergoing left-sided colorectal cancer surgery: randomized clinical trial. British Journal of Surgery (2024).
3. Effects of bowel preparation on the human gut microbiome and metabolome. Scientific Reports (2019).