Fiber intake and laxation in people with normal bowel function: a systematic review

Area of Science:

• Gastroenterology
• Nutrition Science
• Evidence-Based Medicine

Background:

• Optimal evidence-based dietary recommendations for fiber intake remain undefined.
• The impact of dietary fiber on gut motility requires further clarification.

Purpose of the Study:

• To conduct a systematic review and meta-analysis of randomized controlled trials (RCTs) on dietary fiber and gut motility (laxation).
• To assess the effects of varying fiber amounts and types on bowel function in non-infants with normal bowel function.

Main Methods:

• Systematic search of PubMed, Embase, and CINAHL databases up to March 4, 2025.
• Inclusion of 113 RCTs in the general population without bowel dysfunction.
• Categorization of fibers by solubility, viscosity, and fermentability, with Bayesian regression and spline analyses.

Main Results:

• Increased fiber intake softens stool consistency, increases fecal weight and frequency, and shortens gut transit time.
• Low solubility and low fermentability fibers demonstrated the strongest associations with laxation outcomes.
• Effects varied by fiber dose and type, with moderate strength of evidence (SoE).

Conclusions:

• Randomized controlled trials support small to modest effects of dietary fiber on laxation in healthy individuals.
• Fibers with low solubility and low fermentability are most effective for promoting laxation.
• Future research should investigate wider fiber dose ranges and comprehensively report intake.