Psyllium Husk Not Digested

Psyllium Husk Not Digested

An unfermented gel component of psyllium seed husk

promotes laxation as a lubricant in humans.

Am J Clin Nutr, 2000 Sep;72(3):784-9

Marlett JA, Kais TM, Fischer MH.


BACKGROUND: In addition to increasing stool weight, supplements of psyllium seed husk produce stools that are slick and gelatinous.

OBJECTIVE: Our purpose was to test the hypothesis that a gel-forming fraction of psyllium escapes microbial fermentation and is responsible for the characteristics that enhance laxation.

DESIGN: Fifteen healthy adults consumed controlled diets for two 7-d periods, one of which included 8.8 g dietary fiber provided by 15 g/d of a psyllium seed husk preparation. All stools were collected and evaluated and diet was monitored throughout.

RESULTS: Psyllium significantly increased the apparent viscosity of an aqueous stool extract, stool moisture, and wet and dry stool weights. A very viscous fraction, not present in low-fiber stool and containing predominantly 2 sugars that are also found in abundance in psyllium husk, was isolated from psyllium stool.

CONCLUSIONS: In contrast with other viscous fibers that are fermented completely in the colon, a component of psylliumis not fermented. This gel provided lubrication that facilitated propulsion of colon contents and produced a stool that was bulkier and more moist than were stools resulting with use of comparable amounts of other bowel-regulating fiber sources.
PMID:10966900[PubMed – indexed for MEDLINE]

The active fraction of psyllium seed husk.

Proc Nutri Soc, 2003 Feb;62(1):207-9

Marlett JA, Fischer MH.

Department of Nutrition Sciences, University of Wisconsin-Madison, Wisconsin 53706, USA.


A series of experiments and evaluations of fractions isolated from psyllium seed husk (PSH) were used to test the overall hypothesis that a gel-forming component of PSH is not fermented and that it is this component that is responsible for the laxative and cholesterol-lowering properties of PSH. A gel is isolated from human stools collected during a controlled diet study when PSH is consumed but not when the control diet only is consumed. Evaluations of three fractions isolated from PSH suggest that gel-forming fraction B, which is about 55% of PSH, is poorly fermented and is the component that increases stool moisture and faecal bile acid excretion, the latter leading to lower blood cholesterol levels. Fraction C, representing < 15% of PSH, is viscous, but is rapidly fermented. Fraction A is alkali-insoluble material that is not fermented. In concentrations comparable with their presence in PSH, fractions A and C do not alter moisture and bile acid output. The active fraction of PSH is a highly-branched arabinoxylan consisting of a xylose backbone and arabinose- and xylose-containing side chains. In contrast to arabinoxylans in cereal grains that are extensively fermented, PSH possesses a structural feature, as yet unidentified, that hinders its fermentation by typical colonic microflora.

PMD:12749348[PubMed – indexed from MEDLINE]

A poorly fermented gel from psyllium seed husk

increases excreta moisture and bile acid excretion in rats.

J Nutr, 2002 Sep;132(9):2638-43.

Marlett JA, Fischer MH.


Psyllium seed husk (PSH) increases stool output and lowers blood cholesterol levels in humans. PSH and three fractions isolated from it were meal-fed to colectomized rats and fermented in vitro to test the hypothesis that viscous, gel-forming fraction B was responsible for these physiological actions. Control rats were fed 50 g/kg cellulose. The concentration of each PSH fraction in the test meals was equivalent to its concentration in PSH. Yields of the fractions were: A, 171; B, 575; and C, 129 g/kg of PSH. The wet weight and moisture content of ileal excreta (IE) from rats fed test meals containing PSH or fraction B were greater than those measured in excreta from rats fed meals containing cellulose or the other two PSH fractions. Total bile acids in IE did not differ between rats fed PSH or fraction B and were greater in these groups than in the other groups. Fraction A was not fermented during 3 d of incubation; fraction B was poorly fermented, with approximately 30% of the constituent sugars disappearing; and fraction C was rapidly and nearly completely fermented. These results indicate that the gel-forming fraction we isolated from PSH is the physiologically active component of the husks.

PMID:12221223[PubMed – indexed for MEDLINE]

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