The active fraction of psyllium seed husk.
Level 5 - mechanism / opinion, no new human data
Narrative review summarizing mechanistic fractionation and controlled diet studies
PubMed 12749348 · doi:10.1079/pns2002201
What was done
The authors summarized a series of fractionation and controlled diet experiments evaluating three isolated fractions (A, B, and C) of psyllium seed husk (PSH). The studies tested the hypothesis that a non-fermentable, gel-forming component drives psyllium's laxative and cholesterol-lowering effects by assessing stool gel formation, fecal moisture, and fecal bile acid excretion.
What was found
A distinct gel was isolated from human stools during PSH consumption but not during the control diet. Fraction B (approximately 55% of PSH) is poorly fermented, forms a gel, and drives the increases in stool moisture and fecal bile acid excretion. Fraction C (< 15% of PSH) is viscous but rapidly fermented, while fraction A is alkali-insoluble and unfermented; neither fraction A nor C altered stool moisture or bile acid output at natural concentrations. The active fraction was characterized as a highly branched arabinoxylan resistant to colonic microflora fermentation. The abstract provided no specific numerical values or effect sizes for stool moisture, bile acid excretion, or blood cholesterol changes.
Why it matters
The findings pinpoint the specific non-fermentable arabinoxylan fraction responsible for psyllium's therapeutic laxative and lipid-lowering mechanisms, distinguishing its structural resistance to fermentation from typical cereal grain fibers.
Limits
The abstract provides a narrative summary without reporting participant numbers, demographic details, study durations, numerical effect sizes, or statistical significance tests. The precise structural feature that prevents bacterial fermentation of this fraction remains unidentified.
Cited by
- supports Arabinoxylan, which is found in psyllium, clearly lowers blood cholesterol levels.