Psyllium husk is a soluble fiber best known for its ability to treat constipation. But, what other contributions can it make to our health, and is it truly harmless? Read on to discover the other fascinating benefits and side effects of psyllium husk.
What is Psyllium?
Psyllium is a robust herb that grows around the world but is most commonly found in India, which remains the largest producer of psyllium husk today. It is also referred to as Isabghol (Ispaghol in Pakistan), derived from the Sanskrit words “asp” and “ghol,” together meaning “horse flower.” The whole seed has been used in traditional Iranian medicine for hundreds of years.
The inner seed contains many starches and fatty acids, making it an excellent natural additive for animal feed. The outer coat (the husk) is ground down into mucilage, a term describing clear, colorless, gelatinous dietary fiber that confers the majority of health benefits in both humans and animals [R].
Not only does it have health benefits, but its gel-like character makes it a popular addition to foods to produce desired thickening and texture [R].
Psyllium husk is largely composed of carbohydrates (85%), with the remainder consisting of fats, plant ash, and protein [R].
The carbohydrate portion contains twice as much insoluble fiber (cellulose, hemicellulose, lignin) as soluble, both of which are essential to the benefits provided by psyllium husk.
- Soluble fiber: The gel-like material that easily absorbs water, which then causes it to expand
- Insoluble fiber: Consists of the non-digestible, water-resistant plant matter [R]
Mechanism of Action
The dry, fibrous content of psyllium husk draws water into the gut by pulling water from high- to low-moisture environments.
- The soluble portion easily absorbs water, causing it to expand in the gut. This has the dual effect of softening the stool and physically stimulating gut transport.
- The insoluble fiber is not water absorbent but still helps draw water into the gut and physically stimulates gut flow. It also adds bulk, contributing to a larger, more firm stool.
This is the mechanism that psyllium husk is best known for. However, it also binds to muscarinic and 5-HT4 receptors, which would contribute even more to the laxative effect described above.
It may also block calcium channels while activating the NO-cGMP pathway, with the combined effect of decreased gut stimulation. This may explain its paradoxical ability to treat constipation and diarrhea alike [R].
Health Benefits of Psyllium Husk
1) Psyllium Husk Treats Constipation
Adding psyllium husk to your diet is proven to reduce constipation by drawing in and absorbing water as it passes through the gut. This causes the stool to soften and expand, making it simultaneously easier to move while stimulating normal gut flow [R, R].
In multiple small human studies (following up to 15 patients in one study), psyllium husk significantly decreased stool transit time and increased both bulk weight and relative stool softness [R, R, R].
This was achieved without disrupting nutrient absorption [R].
Furthermore, in a multi-site DB-RCT involving 170 patients, psyllium was more superior in softening stool and treating chronic constipation than docusate sodium (a stool softener commonly used in healthcare settings) [R].
A study in rats found that psyllium was more effective than cellulose (insoluble fiber found in most plants) in creating stool moisture, likely due to its soluble fiber content that resists fermentation [R].
2) Psyllium Husk May Relieve Diarrhea
Psyllium husk may also relieve diarrhea, which may seem strange considering its long-proven role in reducing constipation [R].
In 2 human studies (with as many as 39 subjects), psyllium husk increased stool transit time and improved the consistency of the stool in patients with diarrhea. In the same studies, patients with constipation had decreased transit time [R, R].
While the mechanism for controlling diarrhea is less understood, this study in living mice (in addition to rabbit/pig guts) may shed some light:
- Psyllium husk treated constipation in mice. But, it also stimulated muscarinic and 5-HT4 receptors of the gut, which would complement the physical stimulation it produces.
- When psyllium husk was given to mice with diarrhea, transit time was slowed and stool consistency improved. Receptor pathways were changed in these mice as well, specifically blocking calcium ion channels and activation of the NO-cGMP pathways, which would combine to inhibit gut flow [R].
With that information in mind, it may help to think of psyllium husk as a “regulatory” fiber rather than strictly anti-diarrheal or anti-constipation. This makes it an excellent option for patients with irritable bowel syndrome, who often have diarrhea and constipation.
A randomized controlled pilot study evaluated psyllium husk in 60 cancer patients with radiation-induced diarrhea, showing a decrease in both the incidence of diarrhea and the severity of symptoms [R].
Sometimes diarrhea is an unavoidable side-effect of another medication. Patients with liver failure may have a liver-caused brain injury, where ammonia builds up in the blood and causes altered mental status. This is treated with lactulose, which can cause significant amounts of diarrhea [R].
A randomized crossover study of 8 patients showed that psyllium husk delayed stomach emptying and reduced the speed of gut transit, possibly due to the poor fermentation of psyllium husk compared to other fibers [R].
3) Psyllium Husk May Lower Blood Sugar Levels
Multiple types of fiber have the ability to curb your blood sugar [R].
In multiple double- and single-blind RCTs (with as many as 125 subjects), psyllium husk significantly reduced both fasting and after-meal blood sugar levels, reduced insulin spikes, and decreased the absorption of glucose, with a reduction in HbA1c [R, R, R, R, R, R].
Similar results were seen in a meta-analysis of 7 studies of 378 patients, including 3 that were randomized and blinded [R].
In a small DB-RCT of 49 patients, psyllium husk not only improved fasting blood sugar and HbA1c levels but enhanced patient tolerance to metformin (a very common oral medication for treating type 2 diabetes) [R].
It is important to note that these results were achieved when psyllium husk was consumed with meals.
4) Psyllium Husk May Aid in Weight Loss
Psyllium husk may be able to help with weight loss by increasing fullness [R].
In a 200-subject DB-RCT, consuming psyllium husk with meals increased fullness and reduced subjective appetite sensation, resulting in weight loss (approximately 10 lbs.) [R].
The mechanism behind this may be explained by a small RCT of 12 patients that found that psyllium delayed stomach emptying, which likely contributes to the increased fullness and reduced appetite [R].
Another triple-blind study of 17 females revealed the same changes in fullness and appetite and found that subjects inherently reduced their daily fat intake [R].
Not only is psyllium husk associated with weight loss, but another double-blind RCT study of 72 patients showed that it reduced BMI and total body fat percentage. The study does note that while this was achieved with psyllium husk alone, combining it with a healthy diet produced superior results [R].
5) Psyllium Husk May Lower Cholesterol
Taking psyllium husk could improve your overall cholesterol profile [R].
This was observed again in a meta-analysis (21 RCTs and total of 1,030 subjects), though it noted the reduction in total cholesterol occurred faster than the drop in LDL. It also indicated that the effects may be dose- and timing-dependent [R].
Bile acid production and subsequent excretion is a primary method of eliminating blood cholesterol [R].
A small single-blind RCT studied the effects of psyllium husk in 45 teenage males at risk for developing metabolic syndrome. Not only did they observe an improvement in their cholesterol profiles, but there was an improvement in overall body composition/distribution of body fat [R].
6) Psyllium Husk May Decrease Blood Pressure
Psyllium husk might help you treat high blood pressure. One small RCT of 36 subjects showed that eating fiber and protein provided additive reductions in systolic pressure, averaging 5.9 mmHg with both. These findings were independent of age, gender, weight change, alcohol intake, or urinary sodium/potassium [R].
A study in rats prone to salt-driven hypertension found smaller increases in pressure when psyllium husk was added to the diet and proposed that this was due to the psyllium causing increased fecal excretion of sodium [R].
Although this was a rat study, this is an important consideration as patients with heart failure are highly sensitive to dietary sodium, often ending up in the emergency department after a holiday. This increase is correlated to overeating during the holiday, emotional stress, and reduced exercise. While attention to diet is the best intervention, psyllium husk may curb some of the short-term damage [R].
A separate SB-RCT following 72 healthy people on a regular diet compared fiber and healthy diet separately against placebo for 12 weeks. It showed that psyllium husk alone initially lowered systolic and diastolic pressures but the effect did not last for the full 12 weeks, whereas healthy diet alone had lasting effects and created larger improvements in blood pressure [R].
Given the data, psyllium husk may have an adjunctive role in treating high blood pressure, but more studies are needed.
7) Psyllium Husk May Treat Irritable Bowel Syndrome and Ulcerative Colitis
We know psyllium husk has a role in treating both diarrhea and constipation, as previously stated. These are also symptoms of irritable bowel syndrome and ulcerative colitis [R].
One RCT of 28 subjects looked specifically at whether psyllium husk plays a role in patients with irritable bowel syndrome, discovering that psyllium husk eliminated symptoms and further showing that stopping psyllium husk causes a relapse [R].
A placebo-controlled trial of 29 subjects with ulcerative colitis in remission found superior control of gut symptoms using psyllium husk vs. placebo. Four patients were unable to finish the trial due to relapse, noting that three were in the placebo category [R].
8) Psyllium Husk May Be Anti-Amoebic
Interestingly, psyllium husk may help fight amoebic infections. A study in cells found that a water- and petroleum-based husk extract inhibited 3 Entamoeba species, including histolytica, which causes a wide array of symptoms in humans. The petroleum-based extract showed much greater inhibition of growth [R].
9) Psyllium Husk May Prevent Colon Cancer
In a study of rats exposed to a known colon carcinogen (cancer-causing chemical), psyllium husk strongly reduced the incidence of tumors, compared to cellulose and control [R].
However, there are several case reports that you should know about.
- Two studies found a total of 11 nurses with occupational asthma linked to psyllium exposure:
- One looked at 5 nurses who had symptoms after preparing psyllium husk solutions for patients. They had all tested positive for IgE antibodies to psyllium, and inhalation challenges produced symptoms in all of them. One patient had reactive airway closure and required 3 hours of assisted ventilation [R].
- The other study looked to see if nurses with known exposure reactions could have a reaction to ingestion. All 6 developed airway symptoms, one requiring urgent intervention [R].
- One case study of a 40-year-old woman who had been taking a psyllium-containing laxative for 2 years found that the woman developed a whole-body itching (pruritic) rash, sparing only her face. The symptoms resolved when psyllium was stopped and started again with an oral challenge. She was IgE positive for psyllium antibodies. She underwent sensitization therapy to allow her to continue using the laxative. It is important to note that her sensitivity was protein-based and likely due to inner seed exposure, rather than the husk [R].
- One case study of a patient on oral lithium (a medication used to treat bipolar disorder) experienced a drop in blood lithium levels while taking psyllium husk, which returned to normal after cessation of psyllium [R].
- Four patients developed small bowel obstruction after psyllium was used as an oral contrast agent for CT or MRI scans. The takeaway was that caution must be used when considering psyllium husk in anyone with suspected bowel strictures or active inflammation [R].
Limitations and Caveats
Most of the studies were done in humans and even include meta-analyses, but overall the sample sizes in these studies were small and sometimes limited by gender or other restrictions. Care should thus be taken when considering psyllium husk therapy (as you should with any supplement).
As mentioned above, there is a case report of psyllium interfering with lithium absorption [R].
It may also delay digoxin (a common heart failure medication) absorption, but is unlikely to prevent it or cause any clinically significant effect [R].
The LexiComp Drug Interactions used by physicians to screen for drug interactions gives psyllium/digoxin a B risk rating, meaning they may interact with each other but no action is needed as there is little concerning evidence [R].
Other sources suggest that psyllium may interfere with the absorption of tricyclic antidepressants (amitriptyline, doxepin, imipramine), seizure medications (carbamazepine), bile acid sequestrants (cholestyramine, colestipol), and a variety of diabetes medications. However, there is no evidence of this.
Natural Sources (or Forms of Supplementation)
Psyllium husk is sold over the counter in the whole form, granulated, encapsulated, or powdered. Because it lacks a distinct flavor, functions as a food thickener, and stores easily, psyllium has been fortified into many food products, especially ice cream and high-fiber cereals [R].
The Lexicomp drug database recommends the following dosages:
- For constipation: 2.5 to 30 g/day in divided doses (In children age 6 to 11 years old: 1.25 to 15 g/day in divided doses).
- For reduction of coronary heart disease: At least 10.2 g/day (translates to at least 7g soluble fiber/day)
- For adjunctive therapy of type 2 diabetes: 6.8 to 13.6 g/day split between 2 doses
- For irritable bowel syndrome: 10 g/day over 1 or 2 doses [R]
Regarding bagged, whole husks:
- People find that mixing whole husks in liquid produces a thick, grainy substance that is difficult to consume unless they finish it quickly. However, they say it is less likely to get stuck in your teeth and on the glass than the powder.
- A user who added it to their cooking found the husks much more palatable, especially in gluten-free cooking or on a dry cereal with fruit.
- Multiple users endorse improvement in their stool form with whole husks, requiring less toilet paper.
Regarding psyllium capsules:
- Users generally find the capsules easy to use and work with compared to the bagged whole husks or powder, especially when trying to make a drink.
- People appreciate the lack of artificial sweeteners.
- Again, users state that psyllium capsules support their stool regularity.
Regarding bagged, powdered psyllium husk:
- Many users add a spoonful to their water or on food to get their daily fiber intake.
- One user compared it to Metamucil in effectiveness but appreciated the lack of sugar in the psyllium powder.
- Multiple users say they dislike the texture it produces when mixed in liquids and must be consumed quickly, with one person describing it as “a raw egg texture.”
- Another user stated appreciated that it had no foul taste and wasn’t too bulky, adding it to their hot cereal in the morning.
- Users state that the powder is helpful in maintaining bowel regularity.
Summary: Psyllium can be difficult to consume in a drink, and if you choose to do so, people recommend drinking it quickly before it thickens. Alternatively, have it over food that takes well to thickening (oatmeal, for example). Experiences with encapsulated psyllium seem to be positive overall.