Psyllium

Psyllium /ˈsɪliəm/, or ispaghula (isabgol) /ˌɪspəˈɡuːlə/, is the common name used for several members of the plant genus Plantago whose seeds are used commercially for the production of mucilage. Psyllium is mainly used as a dietary fiber to relieve symptoms of both constipation and mild diarrhea, and occasionally as a food thickener.[1] It is commonly used as a food ingredient in manufactured breakfast cereals which may contribute to a healthy lifestyle by improving blood cholesterol levels and gastrointestinal function.[2]

Psyllium husk

Use of psyllium in the diet for three weeks or longer lowers blood cholesterol levels in people with elevated cholesterol,[2][3] and lowers blood glucose levels in people with type 2 diabetes.[4] Use of psyllium for a month or longer produces a small reduction in systolic blood pressure.[5]

The plants from which the seeds are extracted tolerate dry and cool climates and are mainly cultivated in northern India.

Uses

Preparations containing psyllium are sold under brand names such as Metamucil (in the US and elsewhere) and Fybogel (in the UK).

Constipation

Psyllium is mainly used as a viscous, soluble dietary fiber, which is not absorbed by the small intestine. The purely mechanical action of psyllium mucilage is to absorb 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: it absorbs water and subsequently softens the stool. It does increase flatulence to some degree.[6]

High blood cholesterol

Psyllium fiber is an effective and well-tolerated part of a prudent diet for the treatment of mild to moderate hypercholesterolemia, functioning by interfering with cholesterol absorption.[7] In 1998, the U.S. Food and Drug Administration approved a health claim for dietary psyllium as a soluble fiber that would reduce the risk of heart disease.[8] What was proven in clinical trials was that seven grams or more per day of soluble fiber from psyllium seed husk would sufficiently lower total cholesterol and low density lipoprotein cholesterol in people with hypercholesterolemia, accepted biomarkers for risk for coronary heart disease. None of the clinical trials were large enough or long enough to confirm that consuming psyllium had the expected disease effect. The science available at the time was summarized in a review,[9] and has since been confirmed in a meta-analysis that incorporated more evidence.[7] For a food or dietary supplement for the FDA-allowed health claim it must contain at least 1.7 grams of psyllium per serving, i.e., 25% of the amount designated as effective. Psyllium joined whole oats, barley and sources of beta-glucan soluble fiber as deserving the coronary heart disease risk lowering label claim.[8] The European Food Safety Authority – responsible for reviewing health claim proposals for the European Union – has no record of having considered a psyllium health claim for lipid management.

Type 2 diabetes

In 2014 the U.S. Food and Drug Administration approved a Qualified Health Claim (QHC) for psyllium being a benefit for people with diabetes. Any company wishing to use this QHC must use the FDA-approved wording on the label: "Psyllium husk may reduce the risk of type 2 diabetes, although the FDA has concluded that there is very little scientific evidence for this claim." [10] A meta-analysis published after the FDA decision reported that psyllium provided before meals improved fasting blood glucose and glycated hemoglobin (HbA1c), but that the larger effect was seen in people diagnosed with and being treated for type 2 diabetes, and only a modest improvement for people classified as pre-diabetic.[4] The European Food Safety Authority - responsible for reviewing health claim proposals for the European Union - has no record of having considered a psyllium health claim for glucose management.

Food

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.

Veterinary Medicine

Psyllium fiber supplements are commonly used in veterinary medicine to treat cases of sand impaction in horses by aiding in the elimination of sand from the colon.[11]

Adverse effects

Fibre generally has few side effects.[12]

  • Psyllium can cause bowel obstructions or bezoars, if taken without adequate amount of water.[13][14]
  • Gas or stomach bloating may also occur.[12]
  • Choking is a hazard if psyllium is taken without adequate water as it thickens in the throat.[15]

Allergy

Psyllium can cause allergic reactions, including anaphylaxis.[16] Psyllium may act as a potent inhalant allergen capable of eliciting asthma symptoms.[17] Health care professionals at geriatric care hospitals, who are frequently exposed to psyllium in the laxatives administered to patients, are commonly IgE sensitized to psyllium (13.8%), and 8.6% have clinical allergy to psyllium.[18] Pharmaceutical manufacturing employees who have been exposed to psyllium during the processing have developed occupational asthma and IgE sensitization.[19] In order to protect sensitized workers, psyllium has an extremely low occupational exposure limit of 150 ng/m3.[20]

Mechanism of action

The soluble fibre in psyllium is the polysaccharide heteroxylan, a hemicellulose.[21]

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 (i.e. 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.

Cultivation

The genus Plantago contains over 200 species. P. ovata and P. psyllium are produced commercially in several European countries, the former Soviet Union and India. Plantago seed, known commercially as black, French, or Spanish psyllium, is obtained from P. psyllium, also known as P. arenaria. Seed produced from P. ovata is known in trading circles as white or blonde psyllium, Indian plantago, or isabgol. Isabgol is the common name in India for P. ovata. it is known as Aspaghol in Pakistan, coming from the Persian asp and gul, meaning "horse flower", which is descriptive of the shape of the seed. India dominates the world market in the production and export of psyllium.

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.

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 Arizonan 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.

Plantago wilt (Fusarium oxysporum) and downy mildew (Peronospora alta) are the major diseases of Isabgol. White grubs and aphids are the major insect pests.

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 winnowed.

Harvested seed must be dried to 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.

References
  1. Slavin, Joanne (22 April 2013). "Fiber and prebiotics: Mechanisms and health benefits". Nutrients. 5 (4): 1417–1435. doi:10.3390/nu5041417. ISSN 2072-6643. PMC 3705355. PMID 23609775.
  2. Williams, Peter G. (1 August 2014). "The Benefits of Breakfast Cereal Consumption: A Systematic Review of the Evidence Base". Advances in Nutrition. 5 (5): 636S–673S. doi:10.3945/an.114.006247. ISSN 2156-5376. PMC 4188247. PMID 25225349.
  3. Jovanovski, Elena; Yashpal, Shahen; Komishon, Allison; Zurbau, Andreea; Blanco Mejia, Sonia; Ho, Hoang Vi Thanh; Li, Dandan; Sievenpiper, John; Duvnjak, Lea; Vuksan, Vladimir (15 September 2018). "Effect of psyllium (Plantago ovata) fiber on LDL cholesterol and alternative lipid targets, non-HDL cholesterol and apolipoprotein B: a systematic review and meta-analysis of randomized controlled trials". The American Journal of Clinical Nutrition. 108 (5): 922–932. doi:10.1093/ajcn/nqy115. ISSN 0002-9165. PMID 30239559.
  4. Gibb RD, McRorie JW, Russell DA, Hasselblad V, D'Alessio DA (December 2015). "Psyllium fiber improves glycemic control proportional to loss of glycemic control: a meta-analysis of data in euglycemic subjects, patients at risk of type 2 diabetes mellitus, and patients being treated for type 2 diabetes mellitus". Am. J. Clin. Nutr. 102 (6): 1604–14. doi:10.3945/ajcn.115.106989. PMID 26561625.
  5. Khan, K.; Jovanovski, E.; Ho, H.V.T.; Marques, A.C.R.; Zurbau, A.; Mejia, S.B.; Sievenpiper, J.L.; Vuksan, V. (2018). "The effect of viscous soluble fiber on blood pressure: A systematic review and meta-analysis of randomized controlled trials". Nutrition, Metabolism and Cardiovascular Diseases. 28 (1): 3–13. doi:10.1016/j.numecd.2017.09.007. ISSN 0939-4753. PMID 29153856.
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  8. Sec. 101.81 Health claims: Soluble fiber from certain foods and risk of coronary heart disease (CHD) U.S. Food and Drug Administration, Code of Federal Regulations Title 21.
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