What are lentils

Lentil (Lens culinaris; Family: Fabaceae) is an annual indigenous plant from Western Asia and other parts of the world, including North America. The lentil is an edible pulse 1). Lentil is a bushy annual plant of the legume family, known for its lens-shaped seeds, which has the most significant dietary compositions, containing macro- and micro-nutrients 2). Lentil is about 40 cm (16 in) tall, and the seeds grow in pods, usually with two seeds in each. Lentils play an important role in crop rotation and the ability to fix atmospheric nitrogen.

Lentils are the world’s oldest cultivated legume, so it’s no surprise that lentils have become a staple across the globe – from India to the Middle East, Europe, and the Americas. Like beans, lentils add a great high-fiber and high-protein element to many meals. Because of their size, lentils cook much more quickly than dried beans and do not have to be soaked before cooking. They are extremely versatile and inexpensive, which makes them an accessible form of high-quality protein.

Lentils exist as a spectrum of colors, which includes yellow, orange, red, green, brown or black, depending on the cultivar, the composition of the seed coats and cotyledons 3). The color of dehulled seeds is mainly associated with the cotyledon color, which could be yellow, red or green. While the color of the intact seed is based on the seed coat, it could be tan, brown, green, gray or black. The seed coats of lentil have a higher amount of flavan-3-ols, proanthocyanidins and some flavonols. This suggests that lentil featuring green and gray seed coats might be more promising for a health-promoting diet. According to the Food and Agriculture Organization statistics report in 2014, the global production of the lentils was primarily cultivated and harvested by Canada and India, which were estimated to be 1.99 million and 1.1 million metric tons, followed by Turkey (0.34 million), Nepal (0.22 million) and China (0.125 million). The evidence demonstrated that the consumption of lentils is highly associated with reductions in the incidence of degenerative diseases including diabetes, cardiovascular disease (CVD) and cancers. There has been an increase in scientific interest of the study of lentils as a functional food due to their high nutritional compositions, nutritive value and the presence of bioactive secondary metabolites. These bioactive compounds in lentils play a vital role in the prevention of degenerative diseases in humans and a significant role in improving health.

Lentil Types

There are four main categories of lentils: brown, green, red/yellow, and specialty.

Brown Lentils

Brown lentils are the most common variety – any bag in the grocery store that says “lentils” without any other descriptor is most likely full of brown lentils. This variety can range in color from khaki brown to dark black and has a mild, earthy flavor.

Good For:

This variety holds its shape well during cooking, making it ideal for use in warm salads, casseroles, soups, and stews. Brown lentils also work well in veggie burgers or vegetarian meatloaf.

To Cook:

In a medium pot, combine 1 cup dry brown lentils with 2½ to 3 cups of water. Bring to a boil and then simmer for 35–45 minutes until tender. If they will be used in a soup or stew, add them to the pot with about 40 minutes cooking time left.

Green Lentils

Green lentils are extremely similar to brown lentils, but they have a more robust and slightly peppery flavor and come in a range of sizes. Green lentils can vary in color from a pale or spotted green to a green-slate color with hints of blue and black. Pro tip: Green lentils are a great (and less expensive) substitute for the famous French Puy lentils.

Good For:

Like brown lentils, green lentils retain their shape well. This, combined with their strong flavor, makes green lentils ideal for salads or side dishes.

To Cook:

Combine 1 cup lentils with 2½ cups water. Bring to a boil and simmer 35–45 minutes until tender. (Don’t forget to flavor the cooking water with some aromatics or herbs for a tastier end product.)

Red and Yellow Lentils

This variety of lentil ranges in color from golden yellow to orange and red. They are also the only variety sold “split,” meaning they processed into smaller lentil bits. These somewhat sweet and nutty lentils are very common in Indian and Middle Eastern cuisine and are the key to classic dishes such as Indian dhal.

Good For:

Because of their “split” nature, this variety of lentil tends to disintegrate when cooked, making them ideal to use in soups or stews (especially as a thickener), and in casseroles or any other dish where they are pureed.

To Cook:

Split lentils cook quickly, usually in about 15–30 minutes.2425 When you’re using them in a soup or stew, just add them to the pot with 15–30 minutes left in the cooking time. When cooking them on their own, bring 1½ cups water and 1 cup dry lentils to a boil, then simmer until tender, 10–15 minutes.

Specialty Lentils

There are many varieties of specialty lentils, but two are most common: Black beluga and Puy. Both varieties are about one-third of the size of brown or green lentils and have a rich, earthy flavor.

Black Beluga Lentils

When cooked, black beluga lentils are shiny, tiny, and black – they look kind of like caviar: hence their name.

Good For:

Thanks to their rich, earthy flavor, soft texture, and beautiful appearance, these lentils make a great base for salads or as a feature with any kind of protein.

To Cook:

Combine 2¼ cups water and 1 cup lentils. Bring to a boil and simmer 25–30 minutes or until tender.

Puy Lentils

Puy lentils are grown in the volcanic soil of a specific region in central France called Le Puy. Puy lentils are known for their dark, bluish-slate-green color and rich, peppery flavor.

Good For:

These high-quality lentils should star as the center of a meal. They make a great base for meat or fish, or can be easily featured in a side dish or main dish salad.

To Cook:

Combine 2½ cups water with 1 cup lentils. Bring to a boil and simmer 20–30 minutes until tender.

Whether in a salad or soup or as the base of a main dish, lentils make a hearty and healthy addition to any meal. If using a recipe isn’t possible, it’s easy to whip up a tasty lentil-based dish without a lot of direction. Follow the guidelines regarding water to lentil ratio, and add plenty of flavorings to the water itself – an onion (quartered), a bay leaf, or a bundle of other herbs – to flavor the lentils as they cook. Serve with a pan of roasted vegetables and a piece of meat for an easy, complete meal. Lentils easily take the place of any hearty grain or legume in most recipes or cooking applications.

Figure 1. Lentils


Lentils Preparation, Cooking, and Storage

Lentils are sold in two forms: canned and dried. While canned are good for ready-to-eat uses such as a quick salad or side dish, the dried version works well for soups and stews, salads, and sides. A bag of dried lentils can really last forever, but they are best used within a year of purchase (or by the date printed on the package). Once the bag is opened, store any remaining lentils in an airtight container and keep them in a cool, dry place.

One benefit of lentils is that they can be cooked in less than an hour. While it seems like an unnecessary step, don’t skip rinsing your lentils and sifting through them before cooking to remove any stones or debris. It is rare to find stones, but it does happen. When cooking, treat lentils more like pasta than rice – the lentils do not need to absorb every bit of cooking liquid the way rice does, but you also don’t need to completely flood the lentils like you would pasta. As a general rule, one cup of dried lentils yields two to two-and-a-half cups of cooked lentils.

Because of their rather delicate, earthy flavor, lentils work well in a variety of dishes and in almost any type of cuisine. The best time to add flavor to lentils is during the cooking process. Don’t be afraid to get creative. Adding half an onion (peeled), a few cloves of crushed garlic, a bundle of herbs, or a bay leaf to the cooking liquid and a pinch of salt gives lentils plenty of flavor, especially when they’re the base for a salad or side dish.

Lentils nutrition facts

Nutritional compositions of raw, sprouted and cooked lentils are summarized in Table 1. According to the USDA National Nutrient Database, 100 g of raw lentils (variety unspecified) provide 352 calories; the same weight of cooked lentils provides 116 calories. Raw lentils are 8% water, 63% carbohydrates including 11% dietary fiber, 25% protein, and 1% fat (see Table 1). Lentils are a rich source (20% or more of the Daily Value, DV) of numerous essential nutrients, including folate (120% DV), thiamin (76% DV), pantothenic acid (43% DV), vitamin B6 (42% DV), phosphorus (40% DV), iron (50% DV), and zinc (35%), among others. When lentils are cooked by boiling, protein content declines to 9% of total composition, and B vitamins and minerals decrease due to the overall water content increasing (protein itself is not lost) 4).

Lentils are known to have the second-highest ratio of protein per calorie of any legume, after soybeans, providing essential and non-essential amino acids to the human body. The predominant proteins in lentils are globulin (47% of the total seed proteins) and an adequate quantity of albumin 5). High quantities of these proteins and essential amino acids in lentils offer an important dietary source for low and middle-income countries 6).

Among 23 pulses, lentils yield the second highest starch percentage of 47.1% and a greater percentage of insoluble dietary fibers 7). The low levels of readily digestible starch (5%) and high levels of slowly digested starch make lentils of potential value to people with diabetes 8). The remaining 65% of the starch is a resistant starch classified as RS1. Lentils have nutritionally important quantities of prebiotic carbohydrates (12.3–14.1 g/100 g of dry lentils), also known as “resistant starch” that  escapes digestion and absorption in the small intestine 9), making lentils a good source of prebiotics 10) that help to keep up the gut microbial environment and prevent gut-associated diseases 11).

Furthermore, lentils are relatively low in fat and sodium, but high in potassium content (1:30 ratio of sodium and potassium) 12). Given that, it is the best dietary food for patients with obesity and cardiovascular disease. Lentil seeds are an excellent vegetable source of iron. Studies have shown that the consumption of cooked lentil in the diet prevents iron deficiency anemia 13), iron being a very important mineral, which is required daily, especially for adolescents and pregnant women. Several minerals (zinc, copper, manganese, molybdenum, selenium and boron) and vitamins (thiamine, riboflavin, niacin, pantothenic acid, pyridoxine, folate, α, β and γ tocopherols and phylloquinone) have been well documented in lentils 14). Moreover, lentils have an average quantity of vitamin K of 5 μg/100 g, as reported by the United States Department of Agriculture (USDA) 15). However, the daily requirement of this vitamin in adults is about 80 μg. The low content of vitamin K renders lentils as safe for patients with cardiovascular disease upon anticoagulant treatment. Overall, lentils are considered as one of the best dietary sources that has health-promoting effects on various illnesses.

On the down side, lentils also have antinutrient factors, such as trypsin inhibitors and a relatively high phytate content. Trypsin is an enzyme involved in digestion, and phytates reduce the bioavailability of dietary minerals 16). The phytates can be reduced by prolonged soaking and fermentation or sprouting.

Table 1. Lentils (raw) nutrition facts

Total lipid (fat)g0.92–1.060.42–0.550.38–0.75
Total dietary fiberg10.7–31.47.9–15.6
Total sugarsg2.03–2.861.80–3.56
Vitamin Cmg3.4–4.512.7–16.51.5–3.0
Vitamin B6mg0.540–0.6980.146–0.1900.178–0.352
Vitamin B12µg0.000.000.00
Vitamin A, RAEµg2.0–2.51.8–2.00
Vitamin A, IUIU32–3935–458–16
Vitamin Emg0.49–0.5500.11–0.22
Vitamin Kµg4.2–5.001.7–3.4
Total saturated fatty acidsg0.154–0.1980.044–0.0570.053–0.105
Total monounsaturated fatty acidsg0.0179–0.1930.08–0.1040.064–0.127
Total polyunsaturated fatty acidsg0.469–0.5260.169–0.2190.175–0.346
[Source 17)]

Bioactive Compounds in Lentils

Various bioactive compounds or secondary metabolites are present in the lentil seed, which are categorized into different functional groups. The bioactive functional groups and their quantity in lentils are listed in Table 2.

Table 2. List of bioactive functional groups in lentils and their biological functions

Bioactive Functional GroupsIndividual ComponentsQuantity in 100 g of LentilsBiological FunctionsReference
Phytosterolsβ-sitosterol15.0–24.0 mgRegulate the membrane fluid18)
campesterol15.0 mg
stigmasterol20.0 mg
Active Proteins
Trypsin/protease inhibitorsBowman–Birk trypsin inhibitors3–8 trypsin inhibitor unit (TIU)/mgAnti-nutritional components; decrease the digestibility of dietary proteins; inhibit the cell proliferation in cancer19)
LectinsLectins or hemagglutinins12.0 mgAbility to agglutinate red blood cells RBC and strong stimulators of murine B lymphocyte proliferation20)
DefensinsDefensins8.0 mgParticipate in the development of innate immunity21)
Dietary FibersFibersInsoluble fibers (93–99.7 mg/g) and soluble fibers (<7 mg/g)Potential effect of hypocholesterolemic, anti-cancer, anti-tumor, antibacterial and hypoglycemic effects22)
Resistant starches25.4 gSignificant contributor to gastrointestinal health and gut microbiota23)
Polyphenols FlavonoidsFlavonols (e.g., quercetin and kaempferol)0.03 to 10.85 and 0.24 to 13.20 mgAntioxidant potential24)
Flavones, flavanonesTotal phenolic content: 26 mg gallic acid equivalents (GAE/100 g fresh wt; total flavonoid content: 21 mg catechin equivalents/100 g, and the condensed tannin content of 870 mg catechin equivalents/100 gAntioxidant activity and potential effect on cardiovascular disease (CVD), diabetes, osteoporosis and neurodegenerative diseases25)
Proanthocyanidins or condensed tannins (e.g., prodelphinidins and procyanidins)
Flavan-3-ols or flavanols (e.g., catechin and gallocatechin)759 mg (GAE)/100 g; glycosides of flavanones: 33.1–186.0 µg; glycosides of flavonols: 9.6–241 µg; dimers procyanidins: 619–1122 µg; trimer procyanidins: 441–498 µg; tetramer procyanidins: 18.5–59.5 µg; galloylated procyanidins 69.3–123 µgAntioxidant activity26)
Anthocyanidins (e.g., delphinidin and cyanidin)
Polyphenols Non-flavonoidsHydroxybenzoic acidsHydroxybenzoic acids: 4.5–28.4 µgAntioxidant activity and potential effect on diabetes, osteoporosis CVD and neurodegenerative diseases27)
Hydroxycinnamic acids (e.g., p-coumaric acid, ferulic acid and sinapic acid)Prodelphinidins 369–725 µg; condensed tannins: 870 mg catechins equivalentAntioxidant activity28)
Stilbenoids, trans-resveratrol-3-O-glucosideGlycosides of trans-resveratrol: 5.5–9.3 µg;Antioxidant activity and potential effect on diabetes and CVD29)
Phytoestrogens: isoflavonesFormononetin, daidzein, genistein, glycitein, matairesinol, biochanin A, coumestrol, lariciresinol, pinoresinol, secoisolariciresinol, coumestrolTotal isoflavones (9.5 μg), total lignans (26.6 μg) and total phytoestrogens (36.5 μg)Antioxidant potential30)
PhytatePhytic acid620 mgInhibit the proliferation of colorectal cancer31)
TriterpenoidsSqualene0.7 mgChemopreventive potential against colorectal cancer32)
SaponinsSaponins25 mgHypoglycemic and antidiabetic potential33)

Polyphenols in Lentils

Lentils have the highest total phenolic content in comparison to six other common legumes, such as green pea, chickpea, cowpea, yellow pea, mung bean and peanut 34). Polyphenols are generally a large group of compounds, classified into different classes, based on the presence of the number of phenolic rings and their structural elements or substituents 35). Two main groups can be identified based on the aromatic rings, which are attached to the heterocyclic rings, known as the flavonoid groups (flavones, flavonols, flavanones, flavanonols, flavanols or catechins, anthocyanins, neoflavonoids and chalcones) and the non-flavonoid groups (simple phenols, phenolic acids, hydroxybenzoic acids, tannins, acetophenones and phenylacetic acids; hydroxycinnamic acids, coumarins, benzophenones, xanthones, stilbenes, lignans and secoiridoids) 36), 37). Various functional polyphenols in the lentils are described according to their classes and subclasses in Table 3.

Table 3. List of polyphenols in lentils

PolyphenolClassesSub-ClassesCompound Name
Catechin gallate
Epicatechin gallate
Kaempferol-3-O-rutinoside 7-O-rhamnoside
4″″-Acetylsagittatin A
Non-flavonoidsPhenolic acidsHydroxybenzoic acidsSyringic acid
Vanillic acid 4-|A-D-glucoside
2,3-Dihydroxy benzoic acid
p-hydroxy benzoic acid
Gallic acid
Hydroxycinnamic acid3-hydroxy cinnamic acid
p-Coumaroyl malic acid
Sinapic acid
Other polyphenolsHydroxycoumarin4-Hydroxy-6-methyl coumarin
[Source 38)]

Health benefits of lentils

Polyphenol-rich lentils have potential health benefits as complementary and alternative medicines, which are exerted in the form of antioxidant, antibacterial, anti-fungal, antiviral, cardioprotective, anti-inflammatory, nephroprotective, antidiabetic, anticancer, anti-obesity, hypolipidemic and chemopreventive activities. Furthermore, lentils are useful as a prognostic marker for various cancers including thyroid and hepatic carcinoma.

Anti-Diabetic Activity of Lentils

Świeca et al. 39) observed that the regular consumption of the germinated lentils is beneficial for the prevention and management of diabetes. Lentils have the ability to improve blood glucose, lipid and lipoprotein metabolism in diabetic and healthy human beings 40). Human diabetes studies of polyphenol-rich lentil seed showed the anti-diabetic potentials of lentils. The regular consumption of cooked lentils (50 g) among diabetic patients leads to significant reductions of fasting blood sugar and glycemic load 41). Reductions of the glycemic index from the diet are due to the presence of polyphenols in the lentils that have been linked with health-promoting impacts on metabolic disorders such as diabetes, obesity, coronary heart diseases and cardiovascular disease 42). Furthermore, in vitro and in vivo studies have also demonstrated that lentils in the diet regulate starch digestibility, glycemic load and the glycemic index, which diminish diabetes complications 43). 44). In a study involving forty- eight overweight and obese type 2 diabetic patients who ate 60 grams of lentil sprouts daily for 8 weeks in addition to the usual medications, diets and exercise pattern 45). Although the weight did not differ significantly between 2 groups (ie. lentil sprouts group and control group who ate normal diet) after 8 weeks intervention. In that short study, the lentil sprouts subjects improved their glycemic control and reduce their serum lipids and increase their HDL “good” cholesterol level after 8 weeks of lentil sprouts consumption and this effect could be due to some bioactive components in lentil sprouts 46). Thus, a diet including lentils appears to be an effective intervention and management strategy for the prevention of diabetes. A large, well-designed randomized controlled trial is needed to assess the potential value of lentils in improving diabetes.

Antioxidant Potential of Lentils

A wide range of in vitro evidence implies that lentils have the highest total antioxidant capacity when they are compared to chickpeas, common beans and soybeans, which were measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing antioxidant power, oxygen radical absorbing capacity, Trolox equivalent antioxidant capacity and total radical-trapping antioxidant parameters [51,52,53,54]. Evidence has shown that lentils have greater oxygen radical scavenging potential compared to various vegetables and fruits, such as onion, horseradish, potatoes, wheat germ, blueberries and sweet cherries. Lentils have different groups of phenolic compounds such as procyanidin and prodelphinidin dimers and trimers, gallate procyanidins, kaempferol derivatives, quercetin glucoside acetate, luteolin derivatives and p-coumaric acid, hydroxybenzoic compounds, protocatechuic, vanillic acid, aldehyde p-hydroxybenzoic, trans-ferulic acid and trans-p-coumaric acid, compared to other legumes, providing greater antioxidant potentials and health-promoting effects. These phenolic compounds in lentils naturally act as antioxidants and have the ability to restrict the formation of reactive oxygen species, as well as superoxide anion by chelating metal ions or inhibiting enzymes 47). Further research is needed to confirm these findings.

Anti-Obesity Activity of Lentils

Large prospective epidemiological studies have reported that the intake of phenolic-rich lentils is inversely connected with the incidence of obesity and diabetes 48). An earlier human study shows that the intake of lentil seed along with pasta and sauce reduces food intake, body weight and waist circumference 49). Furthermore, lentil seed containing flavonoids and fiber enhances satiety and lowers the amount of food intake, which lead to maintaining body weight in obese subjects 50). Observational studies have further reported an inverse relationship between the consumption of lentils and the basal metabolic index or risk associated with obesity 51). Besides that, interventional studies have shown the potential of lentils to inhibit α-glucosidase and pancreatic lipase, which has the ability to decrease glucose and fat digestion and absorption in the intestine. Ultimately, polyphenol-rich lentils control postprandial glucose and fat, which is crucial in the management of diabetes and obesity 52). Flavonoids in lentils have the potential to inhibit the actions of α-glucosidase and lipase, which suggests that dietary lentil consumption could manage post-prandial blood glucose and body weight 53). Further research is needed to evaluate the usefulness of lentils in managing obesity.

Cardioprotective Effect of Lentils

Phenolic-rich lentil seed consumption has been inversely linked with the occurrence of various cardiovascular diseases 54). Lentils containing polyphenols have the potential to reduce blood pressure by angiotensin I-converting enzyme (ACE) inhibitor activity 55). The recent study observed that bioactive compounds (legumin, vicilin and convicilin) in lentil possess higher antioxidant, ACE-inhibitory and cardioprotective activity 56). Besides that, the polyphenol-rich lentil seeds have the ability of antihyperlipidemic, hypohomocysteinemic, anti-cholesterolemic and a cardioprotective effect that reduces the risk of hypertension and coronary artery diseases 57). In the hypertensive animal model, administration of lentils actively reduces the total cholesterol (TC), triglycerides (TG), low density lipoprotein (LDL) and pathological manifestations of cardio-morphometric analysis. These findings reinforce the importance of lentil seed and its diet prescription as a therapeutic potential for hypertensive patients 58). Al-Tibi et al. 59) observed that treatment with lentil seeds reduces the glycemic index and hyperlipidemic effects in the STZ-induced diabetic animal model. In this study, lentils significantly raised the high density lipoprotein (HDL) levels and reduced blood glucose levels in diabetic rats. Concisely, these studies recommend that the dietary consumption of polyphenol-rich lentils should be on a regular basis, having the potential to decrease the risk of cardiovascular and coronary artery diseases by lowering serum total and LDL cholesterol 60).

Antimicrobial Activity of Lentils

Lentils containing flavonoids and lectins have been reported as non-toxic and safe for use in medical diagnostic kits 61). A bioactive peptide called “defensing”, which is isolated from germinated lentil seeds, possesses a broad spectrum of biological activities, including antimicrobial activities against various infections associated with bacteria and fungi 62). It is a group of “host defense peptides” synthesized in the lentil seeds, which are involved in the development of innate immunity. They are tiny, basic, cysteine-rich peptides, containing antifungal activity, which inhibit the growth of Aspergillus niger 63). Likely, “defensins” can interrupt viral digestive enzymes, such as human immunovirus (HIV)-1 reverse transcriptase, which impacts viral replication. “Defensins” have been further observed to block ion channels and to inhibit protein translation. Therefore, “defensing” in lentil seeds along with phenolic compounds acts as a potential inhibitor of microbial growth. Additional studies are needed before a more definitive link between lentils and its alleged antimicrobial activity can be established.

Anticancer Activity of Lentils

The consumption of lentil seeds reduces the incidence of various cancers including colon, thyroid, liver, breast and prostate 64). A large prospective epidemiologic study associated with polyphenol-rich lentils and breast cancer on 90,630 women exhibited an inverse relationship between lentils and the risk of breast cancer 65). Lentil seeds have a high polyphenolic content that potentially could prevent carcinogens through chemo-preventive activities, including the uptake of carcinogens, activation or formation, detoxification, binding to DNA and fidelity of DNA repair 66). Moreover, lectins in lentils have anticancer properties, which have been observed in various in vitro, in vivo and human studies 67). These lectins along with phenolic compounds in lentil seeds have been proven as therapeutic agents. They potentially bind to cancer cell membranes/receptors, causing cytotoxicity, apoptosis and autophagy; thereby, they inhibit the growth of tumors 68). The underlying mechanism of the anticancer potential of lectins and phenolic compounds in lentil is that they bind to ribosomes, which inhibits protein synthesis. Furthermore, this provokes a change of the cell cycle by inducing non-apoptotic G1-phase accumulation mechanisms, G2/M phase cell cycle arrest and apoptosis. In addition to that, this can also activate the caspase cascade in mitochondria and downregulate telomerase activity, which inhibits angiogenesis 69). Thus, lectins and phenolic compounds derived from lentil seeds seem to be promising therapeutic agents against tumorigenesis or cancer cell agglutination and/or aggregation. The lentil seeds and their chemo-preventive potential on colorectal carcinogenesis have been well documented using azoxymethane, significantly reducing the number of dysplastic lesions and neoplasms in the colon of rats 70). In addition, lentils have greater chemopreventive potential when compared to green and yellow peas 71). This is because lentils contain antioxidant bioactive compounds such as flavonoids (flavanones, flavan-3-ols, flavones, flavonols, anthocyanidins and tannins, including condensed tannins or proanthocyanidins) that are greatly responsible for chemoprevention. This chemo-preventive potential is not constrained to polyphenolic-rich lentils or split seeds. More studies are needed in order to establish a definitive link between anti-cancer activity, cancer reduction and lentils consumption.

References   [ + ]