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Fermented Fiber Supplements Are No Better Than Placebo for a Laxative Effect

Abstract

Background

Misconceptions about the effects of dietary fiber and ‘functional’ fiber on stool parameters and constipation persist in the literature.

Methods

A comprehensive literature review was conducted with the use of the Scopus and PubMed scientific databases to identify and objectively assess well-controlled clinical studies that evaluated the effects of fiber on stool parameters and constipation.

Results

The totality of well-controlled randomized clinical studies show that, to exert a laxative effect, fiber must: (1) resist fermentation to remain intact throughout the large bowel and present in stool, and (2) significantly increase stool water content and stool output, resulting in soft/bulky/easy-to-pass stools. Poorly fermented insoluble fiber (e.g., wheat bran) remains as discreet particles which can mechanically irritate the gut mucosa, stimulating water & mucous secretion if the particles are sufficiently large/coarse. For soluble fibers, some have no effect on viscosity (e.g., inulin, wheat dextrin) while others form high viscosity gels (e.g., β-glucan, psyllium). If the soluble fiber is readily fermented, whether non-viscous or gel-forming, it has no effect on stool output or stool water content, and has no laxative effect. In contrast, a non-fermented, gel-forming soluble fiber (e.g., psyllium) retains its gelled nature and high water-holding capacity throughout the large bowel, resulting in soft/bulky/easy-to-pass stools.

Conclusion

When considering a recommendation for a fiber supplement regimen to treat and/or prevent constipation, it is important to consider which fibers have the physical characteristics to exert a laxative effect, and which fiber supplements have rigorous clinical evidence of a significant benefit in patients with constipation.

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Author's contributions

JWM is the guarantor of the manuscript. JWM collected the data and drafted the manuscript. WDC reviewed and edited the manuscript and contributed to the discussion. JWM and WDC approved the final version of the article.

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Correspondence to Johnson W. McRorie.

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Conflict of interest

JWM is a full-time employee of the Procter & Gamble Company, which markets a fiber product (Metamucil). WDC has no conflict of interest.

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McRorie, J.W., Chey, W.D. Fermented Fiber Supplements Are No Better Than Placebo for a Laxative Effect. Dig Dis Sci 61, 3140–3146 (2016). https://doi.org/10.1007/s10620-016-4304-1

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  • DOI: https://doi.org/10.1007/s10620-016-4304-1

Keywords

  • Fiber
  • Supplement
  • Laxative
  • Placebo
  • Ferment
  • Stool