Several studies point to a cholesterol reduction attributed to a diet that includes dietary fiber such as psyllium. Research published in The American Journal of Clinical Nutritionconcludes that the use of soluble-fiber cereals is an effective and well-tolerated part of a prudent diet for the treatment of mild to moderate hypercholesterolemia. Although the cholesterol-reducing and glycemic-response properties of psyllium-containing foods are fairly well documented, the effect of long-term inclusion of psyllium in the diet has not been determined.
Choking is a hazard if psyllium is taken without adequate water as it thickens in the throat (see Psyllium seed husks). Cases of allergic reaction to psyllium-containing cereal have also been documented.
Psyllium is mainly used as a dietary fiber, which is not absorbed by the small intestine. The purely mechanical action of psyllium mucilage absorbs excess water while stimulating normal bowel elimination. Although its main use has been as a laxative, it is more appropriately termed a true dietary fiber and as such can help reduce the symptoms of both constipation and mild diarrhea. The laxative properties of psyllium are attributed to the fiber absorbing water and subsequently softening the stool. It is also one of the few laxatives that does not promote flatulence.
Psyllium is produced mainly for its mucilage content. The term mucilage describes a group of clear, colorless, gelling agents derived from plants. The mucilage obtained from psyllium comes from the seed coat. Mucilage is obtained by mechanical milling/grinding of the outer layer of the seed. Mucilage yield amounts to about 25% (by weight) of the total seed yield. Plantago-seed mucilage is often referred to as husk, or psyllium husk. The milled seed mucilage is a white fibrous material that is hydrophilic, meaning that its molecular structure causes it to attract and bind to water. Upon absorbing water, the clear, colorless, mucilaginous gel that forms increases in volume by tenfold or more.
The United States is the world’s largest importer of psyllium husk, with over 60% of total imports going to pharmaceutical firms for use in products such as Metamucil. In Australia, psyllium husk is used to make Bonvit psyllium products. In the UK, ispaghula husk is used in the popular constipation remedy Fybogel. Psyllium mucilage is also used as a natural dietary fiber for animals. The dehusked seed that remains after the seed coat is milled off is rich in starch and fatty acids, and is used as chicken and cattle feed.
Psyllium mucilage possesses several other desirable properties. As a thickener, it has been used in ice cream and frozen desserts. A 1.5% weight/volume ratio of psyllium mucilage exhibits binding properties that are superior to a 10% weight/volume ratio of starch mucilage. The viscosity of psyllium mucilage dispersions are relatively unaffected between temperatures of 20 and 50 °C (68 and 122 °F), by pH from 2 to 10 and by salt (sodium chloride) concentrations up to 0.15 M. These physical properties, along with its status as a natural dietary fiber, may lead to increased use of psyllium by the food-processing industry. Technical-grade psyllium has been used as a hydrocolloidal agent to improve water retention for newly seeded grass areas, and to improve transplanting success with woody plants.
It is suggested that the isabgol husk is a suitable carrier for the sustained release of drugs and is also used as a gastroretentive carrier due to its swellable and floatable nature. The mucilage of isabgol is used as a super disintegrant in many formulations.
Plantago ovata is an annual herb that grows to a height of 30–46 cm (12–18 in). Leaves are opposite, linear or linear lanceolate 1 cm × 19 cm (0.39 in × 7.48 in). The root system has a well-developed tap root with few fibrous secondary roots. A large number of flowering shoots arise from the base of the plant. Flowers are numerous, small, and white. Plants flower about 60 days after planting. The seeds are enclosed in capsules that open at maturity.
P. ovata is a 119- to 130-day crop that responds well to cool, dry weather. In India, P. ovata is cultivated mainly in North Gujarat as a “Rabi” or post–rainy season crop (October to March). During this season, which follows the monsoons, average temperatures are in the range of 15–30 °C (59–86 °F), and moisture is deficient. Isabgol (P. ovata), which has a moderate water requirement, is given 5 to 6 light irrigations. A very important environmental requirement of this crop is clear, sunny and dry weather preceding harvest. High night temperature and cloudy wet weather close to harvest have a large negative impact on yield. Rainfall on the mature crop may result in shattering and therefore major field losses.
Isabgol grows best on light, well drained, sandy loams. The nutrient requirements of the crop are low. In northern Gujarat, the soil tends to be low in nitrogen and phosphorus and high in potash with a pH between 7.2 and 7.9. Nitrogen trials under these conditions have shown a maximum seed yield response with the addition of 22 kg/hectare (20 lb/acre) of nitrogen.
Seed preparation and germination
P. ovata has small seeds; 1,000 seeds weigh less than 2 grams. Under ideal conditions of adequate moisture and low temperature 10 to 20 °C (50 to 68 °F), 30% of seeds germinate in 5 to 8 days. The seed shows some innate dormancy (3 months) following harvest. Attempts to eliminate this dormancy period by scarification, or by exposure to wet or dry heat, cold, ethylene, or carbon dioxide, are ineffective. Post-dormancy seeds show reliable germination in excess of 90% at 29 °C (84 °F), with lower rates of germination as temperature is increased.
The fields are generally irrigated prior to seeding to achieve ideal soil moisture, to enhance seed soil contact, and to avoid burying the seed too deeply as a result of later irrigations or rainfall. Maximum germination occurs at a seeding depth of 6 mm (1/4 in). Emerging seedlings are frost sensitive; therefore, planting should be delayed until conditions are expected to remain frost free. Seed is broadcast at 5.5 to 8.25 kg/hectare (5 to 7.5 lb/acre) in India. In Arizona trials, seeding rates of 22 to 27.5 kg/ha (20 to 25 lb/acre) resulted in stands of 1 plant/25mm (1 inch) in 15 cm (6 inch) rows produced excellent yields. Weed control is normally achieved by one or two hand weedings early in the growing season. Control of weeds by pre-plant irrigation that germinates weed seeds followed by shallow tillage may be effective on fields with minimal weed pressure. Psyllium is a poor competitor with most weed species.
The flower spikes turn reddish brown at ripening, the lower leaves dry and the upper leaves yellow. The crop is harvested in the morning after the dew is gone to minimize shattering and field losses. In India, mature plants are cut 15 cm above the ground and then bound, left for a few days to dry, thrashed, and winnowing.
Harvested seed must be dried below 12% moisture to allow for cleaning, milling, and storage. Seed stored for future crops has shown a significant loss in viability after 2 years in storage.