Psyllium

Psyllium is the common word used to refer to fibers taken from the plant known as Plantago ovata (Plantago psyllium is used synonymously, and is where the fiber name is derived from); the fiber is characterized by being water soluble (hydrophilic) and gel forming, while possessing low fermentability. It is commonly known by the brand name Metamucil.

Psyllium is used clinically as a bulk laxative, an agent that has laxative effects but secondary to increasing fecal size; a gentler laxative relative to chemical agents like caffeine or senna alexandrina. This bulk occurs due to water and gas absorption in the small intestines and colon to give chyme (made from digested food) more size and softness. This bulk is retained in the colon despite microflora as psyllium is poorly fermented (highly fermented fibers may be metabolized by bacteria in the colon, and water retaining properties with the fiber would be lost in this scenario).

Psyllium is proven to increase fecal size and moisture, and the most common characteristics of stool following supplementation of psyllium are 'soft, sleek, and easily passable.' Relative to other sources of dietary fiber, psyllium appears to be more effective at forming feces and appears to be one of the few fiber sources not associated with excessive flatulence.

Beyond the fecal properties, psyllium appears to be able to reduce total cholesterol and LDL cholesterol in persons with high cholesterol (secondary to the gel forming properties leeching bile acids, and cholesterol being used up to replace hepatic bile acids) and there is a slight reduction of HDL as well. This is common to all dietary fibers and is not unique to psyllium.

There appears to be some glucose reducing properties associated with psyllium supplementation that may benefit diabetics. These are not overly potent, but appear reliable as long as psyllium is taken; cessation of psyllium usage is associated with a loss of the glucose reduction, and this may be common to all soluble dietary fibers rather than just psyllium.

Psyllium may reduce appetite slightly when taken in high doses, but does not appear to be potent or reliable; long term studies using psyllium in the doses for fecal management have failed to find weight reducing properties of psyllium suggesting it is not a good weight management intervention.

On the lower end of dosing, 5g of psyllium is taken once with meals alongside some form of liquid (200mL of water or more) and can be taken at every meal if desired; coingestion of psyllium with a meal is not mandatory although coingestion with water is highly advised.

Acute doses of up to 30g appear to be well tolerated assuming enough water (in these instances, around 500mL or so) are also coingested.

If using psyllium for the fecal forming properties, a daily dose of 15g (thrice daily dosing of 5g) is a good starting point and then the dose can be titrated up or down depending on its effects on fecal formation.

The Human Effect Matrix looks at human studies (it excludes animal and in vitro studies) to tell you what effects psyllium has on your body, and how strong these effects are.

Grade	Level of Evidence [show legend]
	Robust research conducted with repeated double-blind clinical trials
	Multiple studies where at least two are double-blind and placebo controlled
	Single double-blind study or multiple cohort studies
	Uncontrolled or observational studies only

Level of Evidence ? The amount of high quality evidence. The more evidence, the more we can trust the results.	Outcome	Magnitude of effect ? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.	Consistency of research results ? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.	Notes
	LDL-C	Minor	Very High See all 6 studies	Not overly potent reductions of LDL-C, although they seem to reliably occur in persons with high cholesterol
	Blood Glucose	Minor	Very High See all 4 studies	Reductions in blood glucose seen with psyllium seem to occur reliably in persons with high blood glucose, but are transient benefits and not of a remarkable magnitude.
	HDL-C	Minor	Very High See all 3 studies	Similar to the reductions in LDL-C and total cholesterol, the reduction in HDL-C is seemingly small in magnitude and likely not much to be concerned about
	HbA1c	Minor	Very High See 2 studies	Reduction seen in HbA1c was not overly remarkable
	Total Cholesterol	Minor	Very High See all 4 studies	Not unique to psyllium, but has the standard slight reduction of cholesterol that affects persons with high cholesterol. Not strong enough for monotherapy, can be a nice addition to more potent supplements or drugs
	Blood Pressure	-	High See all 3 studies	No real significant effect of psyllium on blood pressure directly, although there may be an insignificant reduction seen with correcting other parameters of metabolic syndrome.
	Triglycerides	-	Very High See all 4 studies	Currently, it does not seem like there is a significant influence of psyllium on circulating triglycerides
	Weight	-	Very High See all 4 studies	No convincing evidence for a weight reducing effect of psyllium.
	Fecal Moisture	Strong	Very High See all 4 studies	Psyllium is the reference drug for increasing water content of stool.
	Fecal Weight	Strong	Very High See all 4 studies	Psyllium tends to be the reference drug for increasing fecal weight, and due to that and the reliability of which this occurs it gets a strong rating
	Appetite	Minor	Very High See all 3 studies	Studies that report appetite note that there is a significant reduction after a meal containing psyllium (relative to no fiber ingestion) although it does not appear to be too remarkable in potency as overall food intake does not appear influenced.
	Blood Flow	Minor	- See study	Study noted an improved augmentation index by 22% alongside a reduction in blood pressure, mechanisms unknown and no reference drug for comparison.
	Carbohydrate Absorption	Minor	- See study	Supplementation of 12g psyllium husk with a test breakfast is able to reduce carbohydrate absorption by around 12% relative to control.
	Fructosamine	Minor	- See study	A decrease in fructosamine has been noted in diabetics supplementing psyllium husk.
	Insulin	Minor	Moderate See 2 studies	A minor decrease in diabetics following supplementation, although it is small in magnitude and does not carry over to nondiabetics.
	Rate of Gastric Emptying	Minor	- See study	No reference drug to compare it to, and thus the potency in psyllium delaying gastric emptying is not certain.
	Uric Acid	Minor	- See study	An 11% decrease in uric acid has been noted in diabetics supplementing with psyllium husk.
	Insulin Sensitivity	-	- See study	No significant alterations of insulin sensitivity in those who are not insulin resistant at baseline
	Iron Absorption	-	Very High See 2 studies	No significant influence on iron absorption; it is possible the inhibitory effect of phytates in the small intestine are negated by the reduced pH in the colon that enhances mineral reuptake
	Flatulence	Notable	- See study	Notably effective as dietary fibers should normally enhance flatus (almost being a 'per se' effect of dietary fiber) yet psyllium has noted the opposite effect.
	Symptoms of Ulcerative Colitis	Notable	- See study	The potency of psyllium husk in controlling remission of ulcerative colitis is comparable to the reference drug mesalamine.
	Intestinal Motility	Minor	- See study	Increases intestinal motility due to being a bulk laxative, but is unlikely to have a strong laxative effect.
	Food Intake	-	- See study	Failed to significantly influence food intake
	Lipid Absorption	-	- See study	A significant reduction of lipid absorption (assessed via fecal lipids) is not yet supported.
	Thermic Effect of Food	-	- See study	Failed to modify the thermic effect of food.

Studies Excluded from Consideration

• Confounded with inclusion of carbohydrates in test wafers^[1]