Combined Magnesium Oxide and Soluble Fibre Supplementation Relieves Functional Constipation and Modulates Gut Microbiota in Adults: A Randomized, Double-Blind, Placebo-Controlled Trial

Abstract

Background: Functional constipation is highly prevalent and is often managed sequentially with osmotic laxatives or fibre alone,
despite their complementary mechanisms. Objective: To synthesise published evidence on combined magnesium oxide and
soluble fibre supplementation for functional constipation and its effects on gut microbiota. Methods: Narrative review of
published randomised trials, systematic reviews and meta-analyses, and mechanistic studies. Findings: Magnesium oxide
reliably increases stool frequency and softens consistency through osmotic, aquaporin-mediated water retention, soluble fibres
such as psyllium and partially hydrolysed guar gum add viscosity-driven bulking and fermentation-dependent microbiota
remodelling, and combined regimens show additive laxation with enrichment of short-chain-fatty-acid-producing taxa.
Conclusions: Combined magnesium oxide-soluble fibre supplementation is a mechanistically coherent, evidence-supported
strategy for functional constipation with favourable microbiota effects.