Perspective Chapter: Flaxseed (Linumusitatissimum L) – Chemical Structure and Health-Related Functions

Abstract

Flaxseed (Linumusitatissimum L.), one of the oldest cultivated crops, continues to be widely grown for oil, fiber, and food. This herb is used in the food culture of some countries with different purposes. Flaxseed is one of the richest plants in terms of some nutrients. Numerous studies have shown that in terms of omega-3 fatty acids, this herb is one of the richest sources in the diet. Also, the lignan content in flaxseed is significantly higher than that in other plants. Also, the lignan content in flaxseed is significantly higher than that in other plants. In this chapter, the structure and chemical properties of this plant have been investigated first, and then the effectiveness of flaxseed in some chronic diseases has been mentioned.

1. Introduction

Modern living presents a challenge to maintaining good health due to the prevalence of various chronic lifestyle disorders. Medical herbs have received the well-deserved attention as a result of the rapidly shifting international health situation and the quick understanding of the negative consequences of improper food preparation and overmedication. Strong demand in foods that can act as medicines is a result of growing understanding of the importance of diet and the pursuit of well-being. Foods or dietary components known as “functional foods” or “neutraceuticals” can also provide health benefits above and beyond those of simple nutrition. Beyond what might be predicted from their typical nutritive value, functional foods improve health. One of the useful compounds that has attracted a lot of attention from researchers in recent years is flaxseed.

Flaxseed (Linum usitatissimum L.) is one of the predominant industrial oils seed crops grown in temperate climates. The terms flaxseed (Linum usitatissimum L.) and linseed are often used interchangeably. The seed oil of this oilseed crop is enriched in α-linolenic acid (ALA) (18:3cisΔ9,12,15). In addition to linolenic and linoleic acids, lignans, cyclic peptides, polysaccharides, alkaloids, cyanogenic glycosides, and cadmium are among the numerous physiologically active substances and elements that concentrate in flaxseed. The majority of a-linolenic acid or lignan-containing extracts have been the subject of biological and clinical studies on flaxseed. In this chapter, we explain about the chemical characteristics and clinical effects of flaxseed in improving health and preventing chronic diseases.

2. Origin and domestication

Flax, whose scientific name is Linum usitatissimum L., which translates to “extremely beneficial,” comes in two primary colors: brown and yellow or golden (also known as golden linseeds) [1]. The genus Linum is a large group with ∼230 species, which subclassed to fivesubgroups including: depending on the number of chromosomes, the shape of flowers, and interspecific adaptability [2]. The section Linum contains the cultivated flax, Linum usitatissimum, which has 30 diploid chromosomes, along with the proposed progenitors L. angustifolium and L.bienne, which share homostylous rather than heterosylous flowers [3, 4].

The seed of the annual herb known as the flax plant, a member of the Linaceae family, is known as flaxseed. This herb is planted in different regions of the world from eastern Mediterranean to India, Western Asia, and the Middle East, and today, it accounts for a part of the global trade of agricultural products of some countries. There is documentation that flax was used as a fiber source in Neolithic societies. Evidence of flax fiber has been found in ancient sites in Israel and Syria [5]. Between 4500 and 4000 BC, flax was farmed in Egypt. It then spread across Switzerland and was discovered much later at Willium Hill in England [6]. Flax is thought to have been introduced to Canada by Lois Hebert, the country’s first farmer, over 400 years ago [7]. Nowadays, the term “flaxseed” refers to the seeds of the flax plant when they are eaten by human, whereas the phrase “linseed” refers to the seeds of the flax plant when they are used for industrial and feed purposes [8]. The usual life cycle of a flax plant is 45–60 days of vegetative time, 15–25 days of flowering time, and 30–40 days of maturity time. It can reach a height of 12–36 meters. In accordance with the cultivar, flax can produce blue, white, pink, or violet flowers. The flax plant’s mature fruit is a five-segmented dry boll or capsule. Two seeds are contained in each segment of the boll; hence, a capsule can contain up to 10 (on average 6–8) flaxseeds [9]. Seeds of flax appear in different colors depending on the amount of tannin pigments in the pigment cells of seed coat and included medium, reddish brown, and light yellow, where the brown seeds are the most abundant form of flaxseeds with higher tannin contents [10]. A commercial flaxseed strain with yellow seeds called Solin (Linola) was introduced and sold in Canada [11].

Since its cultivation began in Mesopotamia about 5000 BC, flaxseed has mostly been used for the production of cloth and paper. As mentioned, the global trade of this plant today accounts for a part of the global economy of agricultural products. Canada is the largest producer of this plant in the world with an annual production of 20 tons, and after this country, other countries such as America, China, India, and Russia are also among the main producers of this plant in the world [12]. As mentioned, the global trade of this plant today accounts for a part of the global economy of agricultural products. Canada and Russia are among the largest producers of this plant in the world, and after this country, other countries such as America, China, India, and Kazakhstan are also among the main producers of this plant in the world [13, 14].

3. Flaxseed structure and chemical composition

An embryo with two cotyledons that is enclosed by a thin endosperm and a smooth, frequently lustrous yellow to dark brown seed coat makes up mature flaxseed, which is oblong and flattened (hull) [15]. Flaxseed sprouts are edible, with a slightly spicy flavor. Whole flax seeds are chemically stable, but ground flaxseed can go rancid at room temperature in as little as 1 week, although there is contrary evidence. A longer amount of time will be prevented from ground flax going rancid by refrigeration and storing in airtight containers. When packed quickly without exposure to air or light, milled flax is impressively resilient to oxidation for 9 months at room temperature and for 20 months at ambient temperatures under warehouse conditions [16, 17].

The components of this herb are summarized in Table 1. Also, the content of vitamins, minerals, and active compounds in flaxseed is summarized in Table 2. The protein content in flaxseed has been reported as 10–30% in some studies [18, 19, 20]. In terms of protein distribution, the highest amount of protein is in the cotyledons of the flaxseed (between 50 and 70%), and about 30% is in the coat and endosperm [21]. The amino acid profile of flaxseed protein is comparable with that of soy. As shown in Table 1, higher amounts of the some amino specially arginine, valine, glycine, leucine, valine, and serine have been found in flaxseed [22]. In terms of essential amino acid index of flaxseed, it has been reported that the score for this index for flaxseed is 69, and this score is near the score for canola and soy, that is, 75 and 79, respectively [23]. Also, according to the Food and Agriculture Organization (FAO) reports, flaxseed score based on the limiting amino acid is 82; however, this score for soybean is 67 [24]. It has also been shown in some studies that 34.3% of the amino acids in flaxseed are essential amino acids, and the ratio of lysine to arginine, which is an indicator of cholesterolemic and atherogenic effects of a protein, is about 0.22–0.37, which reveals that flaxseed is less atherogenic than canola and soybean [25].

Components (%)	Whole flaxseed	Component	g/100 g of flaxseed	Component	g/100 g of flaxseed
Moisture	7.13	α-linolenic acid	22.8	Arginine	9.2
Nitrogen	4.01	Linoleic acid	5.9	Glycine	5.8
Fat	41	Oleic acid	7.3	Leucine	5.8
Protein	20	Stearic acid	1.3	Valine	4.6
Total dietary fiber	28	Palmitic acid	1.2	Serine	4.5
Ash	3.4	Glutamic acid	19.6	Soluble Fibers	4.3–8.6
		Aspartic acid	9.3	Insoluble Fibers	12.8–17.1

Table 1.

The most important flaxseed components.

Components	g/100 g of flaxseed	Component	g/100 g of flaxseed	Phenolic Compounds mg/100 g of flaxseed
Calcium	236	δ-tocopherol	10	Secoisolariciresinol	165
Magnesium	431	vitamin C	0.5	Laricinesol	1.7
Phosphorus	622	vitamin B1	0.5	Pinoresinol	0.8
Potassium	831	vitamin B2	0.2	Total Flavonoids	35–70
Sodium	27	vitamin B3	1.2
Zinc	4	vitamin B6	0.6
Iron	5	Pantothenic acid	0.6
Manganese	3	Phenolic Compounds mg/g flaxseed powder
γ-tocopherol	522	Ferulic acid	10.9
α-tocopherol	7	Chlorogenic acid	7.5
		Gallic acid	2.8

Table 2.

The content of vitamins, minerals, and active compounds in flaxseed.

The Canadian Grain Commission examined brown Canadian flaxseed, finding that it typically included 41% fat, 20% protein, 28% total dietary fiber, 7.7% moisture, and 3.4% ash [3]. As reported, flaxseeds are rich in oil (40–46% by seed weight) with a healthy fatty acid profile. In terms of type of fatty acids, flaxseed contains about 73% polyunsaturated fatty acids (PUFAs) and 10% saturated fatty acids. Also, in terms of the type of PUFAs, the evaluation results on different samples of flaxseed show the presence of about 52–57% α-linolenic acid (ALA) and an ω-3/ω-6 ratio of 1:0.3 [26]. Considering that higher amounts of ALA make the oil prone to oxidation and Linola seeds have about 5% less ALA compared with the brown flaxseed, therefore, this type of flaxseed is more resistant to oxidation than brown flaxseed and for applications such as frying and shortenings are more suitable [11].

As shown in Table 2, in terms of minerals and vitamins content, flaxseed is one of the appropriate sources of calcium, phosphorus, potassium, magnesium, and γ-tocopherol [3]. In addition, flaxseed is a good source of some active compounds such as phenolic compounds. It has been reported that some of the bioactive phenolic compounds are ferulic acid, chlorogenic acid, and gallic acid [27]. Cyanogenic glycosides (CG), phytates, lignans, and antipyridoxin factors are some of flaxseed’s minor constituents that have been identified. Flaxseed has amounts of the lignan secoisolariciresinoldiglucoside (SDG) that are 75–800 times higher than those of any other documented plants or vegetables [26]. Flaxseed is one of the best dietary functional foods in terms of supply lignan, and the amount of lignan in it varies between 0.9 and 3% depending on various factors [11]. Based on the evidence in some experimental studies, the lignans in flaxseed have anti-estrogenic effects and may have a preventive role in the pathological process of some hormone-dependent cancers [28]. The most predominant lignan in flaxseed is SDG. Enterolactone and enterodiol, which have antiestrogenic properties and structural similarities to estrogen and can bind to cell receptors to inhibit cell proliferation, are formed from SDG [28]. Numerous items made from flaxseed are being sold in the market and promoted for their benefits as functional foods and nutraceuticals. Whole seeds, ground or milled flaxseed (flour), oil extracted from flaxseed (by pressing; cold-pressed or not), flax meal, the coat of the seed, a portion of the seed that has been removed, flaxseed hull, cyclic peptides (orbitides) from flaxseed oil, and lignan extracts from the flaxseed hull are among them [29]. Some of the experimental studies evaluated the digestibility of proteins in the flaxseed, and in some studies, the digestibility percent of this plant has been reported as 81.4–85.8% [30, 31], and this is near the soybean digestibility percent (digestibility percent = 84–85%) [32]. Also, the flaxseed biological value (BV) ranges from 66.4% to 77.4% [33]. The matrix elements, particularly mucilage and oil, and the earlier preparation of the seeds have an impact on the flaxseed protein digestibility [34]. It has been reported in some experimental studies that elimination of flaxseed mucilage improved protein digestibility to 50% compared with the 12.6% for full-fat and mucilage containing ground flaxseed [35]. Also, it has been reported that some of the other processing methods such as boiling, heat treatment can improve flaxseed protein digestibility [36]. One of the concerns related to flaxseed is allergy to the its proteins. However, to date, the results of several studies have reported rare cases of allergy to the proteins contained in flaxseed. Some researchers believe that this allergy observed in some cases is not due to flaxseed proteins, but the reason is the contamination in some seeds [37].

4. Flax: a functional food

It is appropriate to classify flax as a “functional food” due to the numerous health-promoting components found in both the seeds and the oil. Foods known as “functional foods” have potential health benefits in addition to its nutrient contents. L-arginine, cyanogenic glycosides (CNglcs), and omega-3 fatty acids can be mentioned among the active components in the seeds that cause its positive functions in the prevention and treatment of some chronic diseases. The consumer can currently choose between whole flaxseeds and milled flaxseed in the area of health-related functional foods. These goods are promoted as excellent providers of lignans, dietary fiber, and omega-3 fatty acids. Numerous common foods, including muffins, bread, crackers, tortillas, cereals, and snack bars, include whole flaxseeds. The commercial marketing of flaxseed products as sources of protein for food usage is extremely limited [38].

However, in recent years, some food manufacturing companies use flaxseed to create a pleasant nutty flavor in the preparing cereal and bakery products. Also, due to the fact that flaxseed does not contain gluten, some food companies use flax flour in the production of gluten-free food for celiac patients [39]. Some attempts have been made to fortify breads with flaxseed flour; however, some limitations have made the results not very satisfactory. For example, it has been reported that use of flaxseed flour for bread production resulted in poor texture, crumb color, graininess, volume, and crust color [40]. On the other hand, considering that flaxseed contains PUFA, the use of this plant in the bakery industry and exposure to high heat may cause the oxidation of fatty acids and the production of metabolites such as malondialdehyde (MDA), which have adverse effects on health [41]. However, Cunnane et al. were reported that cooking at the normal temperature and for a limited time does not significantly increase the production of MDA [42]. Antinutritional components included in flaxseed products present a significant obstacle to their use in food products. Linustatin, neolinustatin, and linamarin are CGs that can be found in flaxseed [43]. These substances are broken down by β-glucosidases when the cell structure is disturbed, generating small amounts of hydrogen cyanide, a potent respiratory inhibitor [44]. However, in some studies, it has been reported that usage from some methods such as extraction of flaxseed meal 2–3 times with methanol-ammonia-water, heat treatment, boiling for 5 min in water, and dry and wet autoclaving can decrease CG in flaxseed [45, 46]. Linatine, an antagonist of vitamin B6 (pyridoxine), is also found in flaxseed. Generally, linatine concentrations range from 20 to 100 mg/kg. Before eating, heat processing could be required to eliminate these antinutritional elements [47].

5. Extraction methods

There are a number of methods that have been suggested for extracting oil from flaxseed, most notably mechanical extraction, solvent extraction, supercritical/subcritical fluid extraction, and extraction with microwave or ultrasonic intervention. The constitution and amount of unsaturated fatty acids and active substances extracted using various techniques typically vary significantly due to the complexity of flaxseed oil. Flaxseed oil is traditionally produced through mechanical pressing, which depends on outside machinery to produce oil. Among the advantages of using mechanical methods to extract flaxseed oil can be mentioned the low cost and equipment, no change in the taste of the oil, acceptable quality, and no need to use chemical compounds for the extraction process [48]. It has been reported that using from the double-screw extrusion preserves the flaxseed oil quality and its ALA contents, but there are also some clear disadvantages, including low yield, high residual oil, and significant reduction in concentration of some of vitamin, phospholipids, phytosterols, and antioxidants [49]. Low extraction efficiency is properly remedied by solvent method, and up to 99% of the oil is obtained. However, there are some concerns that the use of acetone, methanol, petroleum ether, n-hexane dichloromethane, ethanol, and heptane may decrease the purity of oil, influence its physiological activities, and even result in potential issues with food safety and environmental contamination. As a result, instead of producing commercial products, this technology is primarily employed for laboratory-size investigation.

Modern methods of oil extraction have received a lot of attention recently, including supercritical CO₂ extraction, microwave-assisted extraction, ultrasound-assisted extraction, and subcritical fluid extraction. Nowadays, one of the modern methods suggested for extracting flaxseed oil is the use of supercritical CO₂ fluid extraction method, which, in addition to the high quality of the oil, preserves the high concentration of omega-3 fatty acids, phenolic compounds, and lignans [50], and the production efficiency is about 25% higher than that in the mechanical method [51]. Using the microwave and ultrasonic-assisted extraction methods compared with the solvent method has significant advantages, including shortening the extraction time, reducing the solvent consumption, thermal damage to the extract, and the loss of bioactive compounds [52]. The commonly used extraction methods are shown in Figure 1.

Figure 1.

Representative extraction methods of flaxseed oil [53].

6. Biological effects of flaxseed and flaxseed fractions

Whole flaxseed, ground flaxseed, flaxseed oil, partially defatted flaxseed meal (typically from expeller pressing), fully defatted flaxseed meal (from solvent extraction), flaxseed mucilage extracts, flaxseed hulls, flaxseed oleosomes, and flaxseed alcohol extracts are some of the flaxseed products that are consumed. These substances each have unique positive health impacts that have been linked to them. In the following, we discuss some of the positive biological effects of flaxseed in improving health and preventing and treating chronic diseases.

7. Central activities

The higher ALA concentration of flaxseed has been linked to the majority of its effects. Three distinct metabolic destinations are possible for ALA: (a) absorption into structural, transport, or storage pools; (b) use as an energy source via beta-oxidation; and (c) extension and further desaturation to produce EPA, DPA, and DHA.

Although alpha-linolenic acid plays a small role in the cell membrane directly, it plays an important role indirectly in the cell structure after being converted into long-chain omega-3 fatty acids such as EPA and DHA [54]. On the other hand, a part of ALA consumed through diet participates in energy production processes in the body through beta oxidation, the results of some studies have shown that the percentage of ALA that participates in beta oxidation is about 33% in menand 22% in women [55]. On the other hand, the ALA present in flaxseed reduces the production of inflammatory eicosanoids through metabolic pathways [56]. Additionally, some of the activities of flaxseed may not be reliant on its fatty acid concentration and type and may instead be caused by the lignan SDG. It has been established that the SDG is the primary lignin in flaxseed, and that the gastrointestinal bacteria convert this lignin into the mammalian lignans enterodiol (ED) and enterolactone (EL) [57].

8. Anti-obesity effects of flaxseed

Obesity is a serious health issue and a significant contributor to the risk of diabetes, heart disease, and cancer. By 2030, it is anticipated that 1.12 billion people worldwide would be obese [58]. Type 2 diabetes, hypertension, inflammation, metabolic syndrome, cardiovascular dysfunction, and non-alcoholic fatty liver disease are among the comorbid conditions that the majority of obese persons have [59]. Also, it has been reported in several studies that obesity is an important risk factor for some type of cancers [60]. As a result, preventing obesity is essential for lowering chronic disease rates. Several studies have evaluated the effect of flaxseed supplementation in obese people. Mohammadi-Sartang in a meta-analysis from 45 randomized controlled trial studies and 2789 participants showed that flaxseed consumption led to a significant reduction in body weight, body mass index, and waist circumference. Also, they found that the flaxseed supplementation caused significant weight loss if flaxseed was taken with a dose higher than 30 grams per day, and the duration of the intervention was more than 12 weeks [61]. Several mechanisms have been proposed for the anti-obesity effects of flaxseed. As mentioned, flaxseed is one of the richest sources of lignan (primarily SDG), and its lignan content is up to 100 times higher than that of some other plants [62, 63]. SDG, a type of purified lignans, has been demonstrated to decrease visceral (abdominal) fat in mice when compared with animals that did not consume SDG [64]. The researchers proposed that a drop in the mRNA levels of sterol regulatory element-binding proteins, which are essential for the synthesis of triacylglycerol, may result from flaxseed’s high amount of SDG [64]. Also, the results of some studies have shown that the lignans in flaxseed regulate the expression of adiponectin and stimulate fat oxidation, all of which prevent excessive fat accumulation and obesity [64, 65]. It has been demonstrated that dietary fiber, especially soluble fiber, has anti-obesity properties that reduce body weight. By delaying gastric emptying, causing sensations of fullness via absorbing significant amounts of water, and/or increasing the levels of short chain fatty acids, which operate to induce satiety by a wide range of mechanisms, dietary fiber can help control weight or aid weight loss [66].

9. Anti-inflammatory action

Inflammation is one of the main factors in the pathology of many chronic diseases. An increase in the level of inflammatory cytokines in the body provides the basis for damage to various tissues. In some studies, it has been shown that flaxseed has strong anti-inflammatory properties due to its many active compounds, especially because of its ALA contents [67]. The results of a meta-analysis study designed and implemented by our team in 2018 showed that supplementing with flaxseed had a significant effect on reducing the concentration of some inflammatory factors including tumor necrosis factor alpha and high-sensitivity C-reactive protein (hs-CRP) [68]. Positive results have also been reported from supplementing with flaxseed in inflammatory diseases such as rheumatoid arthritis [69] and inflammatory bowel diseases [70]. SDG and its metabolites (enterolactone and lignans enterodiol), which are flaxseed-related active chemicals, in particular, have demonstrated anti-inflammatory and antioxidant potential, primarily by inhibiting lipid peroxidation. Additionally, some research has indicated that the flaxseed lignan portion may stimulate the nuclear element (erythroid-derived 2)-like 2, a transcription factor of the antioxidant and detoxifying genes, including NAD(P)H quinone dehydrogenase 1 and heme oxygenase-1 [71]. It’s important to take into account the connections between the microbiome, inflammation, and diet. For instance, flaxseed is the greatest non-bioactive supply of lignan precursors and is transformed into its main metabolites, which have antioxidant activity, in the colon by gut microbiota, which may be altered by the microbial diversity [72]. On the other hand, flaxseed, as one of the richest plant sources of omega-3, can exert its anti-inflammatory effects through the conversion of alpha-linolenic acid into long-chain omega-3 fatty acids such as eicosapentaenoic acid (EPA) and Docosahexaenoic acid (DHA). The production of pro-inflammatory eicosanoids from omega-6 fatty acids, such as prostaglandin E2 (PGE2) and leukotriene B4 (LTB4), suppressed by omega 3 fatty acids and can induce the production of some anti-inflammatory agents such as resolvins and protectins. Together these provide a mechanism to suppress the activity of nuclear transcription factors including nuclear factor kappa B (NF-κB) and thus decrease the production of pro-inflammatoryenzymes and cytokines, such as cyclooxygenase-2(COX-2), TNF-α, and interleukin (IL)-1 [71, 73].

10. Cardiovascular health

Cardiovascular diseases are one of the main causes of death in the world and one of the five main causes of death and disability in most countries. About 2200 Americans every day, or one every 40 seconds, pass away from cardiovascular disease in the United States [74]. Numerous clinical studies, including DART [75], the GISSI Prevenzione trial [76], GISSI-HF [77], have declared that omega 3 supplementation led to a significant cardioprotective effects. Several studies have investigated the cardioprotective effects of flaxseed from different aspects. This includes dietary supplementation with flaxseed and its effects on atherogenesis [78], lipid profile [79], platelet aggregation [80], arrhythmias [81], hypertension [82], and oxidative stress [83]. In a clinical trial on 112 patients with high blood pressure, Toulabi et al. showed that supplementation with 30 grams of flaxseed per day caused a significant decrease in systolic anddiastolic blood pressure [84]. Also, Mahmudiono et al. in a meta-analysis study showed that flaxseed oil supplementation among the patients with metabolic syndrome and related disorders caused a significant reduction in systolic but not diastolic blood pressure [85]. It is unclear how flaxseed lowers blood pressure and how this happens. Weight loss has been advocated as an effective method for treating high blood pressure in overweight and obese people [56]. But according to one study, flaxseed contains peptides that are high in arginine and can lower blood pressure [86]. Furthermore, flaxseed has a high concentration of ALA. It has been extensively evaluated in some studies and shown that ALA can reduce blood pressure and reduce cardiovascular diseases risk [87, 88].

Also, several studies have evaluated the effect of flaxseed on the lipid profile. Hadi et al. in an updated systematic review and dose-response meta-analysis of 62 randomized controlled trials evaluated the effects of flaxseed on lipid profile, and it has been reported that flaxseed supplementation significantly reduced total cholesterol (TC), triglyceride (TG), and low-density lipoprotein cholesterol (LDL-C). However, there were not any significant effects on high-density lipoprotein (HDL-C). Also, they found that flaxseed oil had no effect compared with whole flaxseed or lignin [89]. As mentioned, these beneficial dyslipidemia effects are caused by the content of lignan, phenolic, and ALA in flaxseed. By boosting satiety, lowering caloric intake, and decreasing meal transit time, flaxseed’s high fiber content protects against dyslipidemia. It also stimulates bile acid excretion and reduces bile acid reabsorption through enhanced fecal excretion of cholesterol. Additionally, fiber affects other metabolic processes, such as fatty acid biosynthesis, lipolysis, and cholesterol synthesis by forming short-chain fatty acids that prevent the formation of liver cholesterol [90].

11. Conclusion

Flaxseed is one of the richest herbs in terms of nutrients and active compounds. This herb is known as one of the best dietary sources of omega-3 fatty acids and lignan. This herb is used in different forms, the most common of which are the whole flaxseed, ground flaxseed, and flaxseed oil. Several methods are used to extract flaxseed oil from full flaxseed, from mechanical methods that are part of traditional methods to more modern methods such as microwave and ultrasonic-assisted extraction methods. In recent years, several studies have been conducted on the beneficial properties of flaxseed in the prevention and treatment of chronic diseases as an alternative treatment, which include anti-inflammatory, antioxidant, anti-obesity effects, improved lipid profile, and reduced risk of cardiovascular diseases. Part of these beneficial effects of this plant is due to its high content of lignans. Despite the mentioned beneficial effects, there are also some concerns related to the use of this plant, such as the risk of oxidation of flaxseed oil in higher temperature due to higher content of PUFA and flaxseed contamination with toxins and heavy metals. Also, some researchers have reported concerns regarding the use of this plant in people with hormone-dependent cancers such as breast and ovarian cancer due to its phytoestrogens. Therefore, there is a need for more studies related to the different aspects of using this plant in the daily diet as well as in the prevention and treatment of chronic diseases.

Acknowledgments

The authors thank the Zanjan University of Medical Sciences for their support in preparing resources and articles for writing this chapter of the book. Both authors (MR and JH) contributed equally in writing all parts of this chapter.

Conflict of interest

The authors declare that there was no conflict of interest in the writing of this chapter.