Table 1.

The biological activities of flaxseed and its health-promoting effects.

Biological Activities and the Related Diseases	Compounds Responsible for Biological Activity	Form of Flaxseed	Design of Clinical Trials	Results of the Clinical Trials
Improvement in lipid profile; decreased risk of heart diseases	α-linolenic acid, phenolic compounds, lignans, dietary fiber	Flaxseed pre-mixed in cookies	77 participants; 12-week intervention Intervention group: 10 g of flaxseed or psyllium pre-mixed in cookies per day; control group: cookies without any additives	Reduced total cholesterol level (36.9 mg/dL; p < 0.001), LDL-C (21 mg/dL; p < 0.001), and TG (12.3 mg/dL; p = 0.045); improved HDL-C (6.0 mg/dL; p = 0.316) in the flaxseed group [13]
		Flaxseed oil, roasted flaxseed, ground flaxseed, raw flaxseed	In the group of healthy participants: 2 to 30 g/d of flaxseed; in the group of participants with lipid metabolic disorders: 15 to 40 g per day of flaxseed	Improvement in lipid profile in healthy participants with BMI >25 kg/m2 (SMD: −28.7); (95% CI −54.67–−2.62); (p = 0.031), and in dyslipidemic participants (SMD: −1.41); (95% CI −2.30–−0.79); (p < 0.001); improvement in LDL-C (SMD: −0.69); (95% CI −1.13–−0.25); (p = 0.002), and reduced TG in dyslipidemic participants (SMD: −1.47); (95% CI −2. 21–−0.72); (p < 0.001); increased HDL-C in healthy (SMD: 5.12); (95% CI 2.34–7.90); (p = 0.006) and overweight participants (SMD: 7.92); (95% CI 2.95–12.88); (p = 0.002) with flaxseed supplementation [14]
		Ground flaxseed	70 participants; 12-week intervention Intervention group: 30 g of ground flaxseed per day; control group: normal diet without flaxseed supplementation	Reduction in TG (−13.07 ± 8.31 mg/dL; p < 0.001), and total cholesterol (−16.50 ± 10.87 mg/dL; p < 0.001) and increase in HDL-C (3.67 ± 2.82 mg/dL; p = 0.04) in the flaxseed group [15]
Hypotensive properties; decreased risk of hypertension and other cardiovascular conditions	α-linolenic acid, lignans, dietary fiber	Flaxseed powder	99 participants; 12-week intervention with a control group; intervention groups: 20 or 40 g of flaxseed powder per day	The 40 g group had a significantly lowered SBP (12.24 ± 23.08 mmHg) compared to the 20 g group (2.56 ± 5.99 mmHg) and the control (−1.5 ± 6.3 mmHg) [18]
		Ground flaxseed	110 participants; 6-month intervention with a control group; intervention group: 30 g of ground flaxseed per day	Significant reduction in SBP (−10 mmHg; p = 0.04) and DBP (−7 mmHg; p = 0.004) in the flaxseed group; patients who had elevated BP at the baseline: reduction of 15 mmHg in SBP (p = 0.002) and 7 mmHg in DBP (p = 0.003) [19]
		Flaxseed powder	112 participants with hypertension; 12-week intervention with a control group; intervention groups: 10 or 30 g of flaxseed per day	Decrease in SBP (−13.38 mmHg; p = 0.001) and DBP (−5.6 mmHg; p = 0.001) in the 30 g group [20]
Hypoglycemic properties; decreased risk of type 2 diabetes and insulin resistance	Dietary fiber, α-linolenic acid	Flaxseed pre-mixed in cookies	77 participants; 12-week intervention; intervention groups: 10 g of flaxseed or psyllium pre-mixed in cookies per day; control group received placebo cookies without any additives	Significantly improved fasting glucose (−27.8 mg/dL; p = 0.004) in the flaxseed group [13]
		Flaxseed powder	99 participants; 12-week intervention with a control group; intervention groups: 20 or 40 g of flaxseed powder per day	Reduced HOMA-IR in the group consuming 20 g of flaxseed (0.27 ± 0.65; p = 0.033); significant reduction in fasting glucose in all study participants [18]
		Flaxseed powder	25 participants overweight or obese with pre-diabetes; 12-week study; participants consumed 0 g, 13 g, or 26 g of flaxseed powder per day	Fasting glucose (−2 mg/dL; p = 0.036), insulin (−1.9 mU/L; p = 0.013), and HOMA-IR (−0.6; p = 0.008) significantly decreased in the 13 g group compared to the 26 g group and placebo [23]
Anticancer properties	Lignans, linoorbitides, α-linolenic acids	-	Breast cancer cell lines (SKBR-3 and MDA-MB-231) were divided into two groups; the first was treated with the combination of chemotherapeutic agents and flaxseed lignans for 72 h, and the second was treated only with chemotherapeutic agents	Flaxseed lignans significantly enhanced the cytotoxicity of chemotherapeutic agents against breast cancer cells; the combination of ENL and metformin together in combination with low concentrations of chemotherapeutic drugs was more effective in decreasing cancer cell viability compared to the individual chemotherapeutic drug alone [25]
		-	Acute myeloid leukemia cell lines and a normal lymphoblastic cell line were cultured and treated with various concentrations of the purified flaxseed lignans	After 24 h, 48 h, and 72 h, the percent proliferation of the cells treated with 100 µM of ENL significantly decreased, reaching 55% (p < 0.0001), 46% (p < 0.0001), and 29% (p < 0.0001) in the KG-1 cell line, respectively; and 55% (p < 0.0001), 46% (p < 0.0001), and 40% (p < 0.0001) in the Monomac-1 cell line, respectively; ENL induces apoptosis and increases cellular and DNA fragmentation [26]
		-	Treatment of a variety of cancer cell lines with 0.3% or 0.9% flaxseed oil for 4–6 days	Cancer cells treated with a 10−5 or 10−6 M mixture of fatty acids and the lignans reduced cell growth; treatment with 0.3% flaxseed oil decreased the number of cells by about 50% and treatment with 0.9% flaxseed oil completely inhibited B16-BL6 cell growth [27]
		-	SGC-7901 cells were treated with various concentrations of [1–9-NαC]-linusorb B2 or B3 (80, 120, and 200 μM) for 24 h and subjected to flow cytometric analysis to examine the DNA content after PI staining; the expression levels of CDK2, CDK4, cyclin D3, cyclin E, and p27KIP1 were measured using Western blotting assay	Cell population in the G1 phase of the cell cycle increased from 33.53 ± 1.46% to 35.30 ± 1.59%, 40.03 ± 2.33%, and 46.30 ± 1.45% after treatment with [1–9-NαC]-linusorb B3 of 80, 120, and 200 μM, respectively; the percentage in G1 phase reached 43.50 ± 2.05%, 49.96 ± 1.90%, and 56.45 ± 0.72%, following exposure to [1–9-NαC]-linusorb B2 of 80, 120, and 200 μM, respectively; downregulation of CDK2, CDK4, cyclin D3, and cyclin E, as well as upregulation of p21WAF1/CIP1 and p27KIP1; the disruption of both JNK and AKT played a pivotal role in [1–9-NαC]-linusorb B2-induced G1 phase arrest, but only JNK was involved in [1–9-NαC]-linusorb B3-induce G1 phase arrest [28]
		-	Human breast cancer cell lines and melanoma cell lines were divided into two groups and cultured for 24 h and 48 h; then, were treated with different concentrations of linoorbitides	Cytotoxicity of linoorbitides against cancer cells was cell-type-specific and concentration-dependent [29]
Anti-inflammatory properties	Lignans, phenolic acids, tocopherols, linusorbs	Flaxseed oil	34 participants with hemodialysis; 8-week intervention; intervention group: 6 g of flaxseed oil per day Control group: 6 g of medium-chain fatty acids (59.4% caprylic acid, 39.6% capric acid, 0.7% caproic acid, 0.2% lauric acid, and 0.1% myristic acid)	Reduction in hs-CRP (−1.4 ± 0.5 mg/L; p = 0.05) and sVCAM-1 (−23.0 ± 10.0 mg/mL; p = 0.05) levels in the flaxseed oil group [32]
		-	RAW264.7 and HEK293 cells were treated with either LOMIX (0–200 g/mL), L-NAME (0–1 mM), Pred (0–100 µM), or individual linusorb; then, several in vitro assays (i.e., NO production, real-time PCR analysis, Western blot analysis) and in vivo analyses were carried out	Inhibition of NO production, cell shape changes, and inflammatory gene expression in stimulated RAW264.7 cells through direct targeting of Src and Syk in the NF-κB pathway; alleviation of symptoms of gastritis, colitis, and hepatitis in murine model systems mediated via inhibition of Src I Syk [33]
Influence on the concentration of female sex hormones; reduced risk of breast cancer	Lignans	Ground flaxseed	99 postmenopausal women; 7-week intervention; intervention group: 2 tablespoons (15 g) of ground flaxseed daily Control group: women on a normal diet	Significant increase in total enterolignans (62.3 mg/mL; p < 0.001), serum 2-hydroxyestrone concentration (TER: 1.54 pg/mL; 95% CI: 1.18–2.00; p = 0.002), and 2:16α-hydroxyestrone ratio (TER: 1.54; 95% CI: 1.15–2.06; p = 0.004); change in enterolignan level was positively correlated with changes in 2-hydroxyestrone and 2:16α-hydroxyestrone ratio, and negatively correlated with prolactin levels [34]
Reduction in menopausal symptoms	Lignans	No data available	140 menopausal women; 3-month intervention with a control group; intervention groups: the first group received 5 g of flaxseed daily, the second group received hormone replacement therapy and 5 g of flaxseed daily, and the third group used hormone replacement therapy	Significant decrease in menopausal symptoms and increase in quality of life in women consuming flaxseed. The intensity of menopausal symptoms decreased by 8.7% and 9.8% in two intervention groups (p < 0.05) being supplemented with flaxseed [35]
		Flaxseed extract, ground flaxseed	90 menopausal women; 6-month intervention; intervention groups: 1 g of flaxseed extract containing at least 100 mg of SDG, or 90 g of ground flaxseed containing at least 270 mg of SDG per day Control group: 1 g of collagen daily	In the flaxseed extract group, Kupperman index and hot flashes were reduced by 2.5 (p = 0.007) and 1.6 (p = 0.001), respectively, and in the ground flaxseed group by 3.05 (p = 0.005) and 1.04 (p = 0.035) compared to the control group [37]
Regulation of gut microbiota	Lignans, soluble fiber	Ground flaxseed	9 healthy men; 1-week intervention; each participant ingested 0.3 g of flaxseed for each kg of body weight per day	Significant increase in ENL blood concentration, accompanied by fecal excretion of propionate and glycerol; ENL production was linked to the abundance of Ruminococcus bromii and Ruminococcus lactaris [38]
		Flaxseed mucilage	58 obese postmenopausal women; 6-week intervention with a control group; intervention groups: daily intake of L. paracasei F19 or 10 g of flaxseed mucilage	Alterations in abundance of thirty-three metagenomic species (p < 0.01), including decreased relative abundance of eight Faecalibacterium species in the flaxseed mucilage group [40]
Increase in the frequency of evacuation and improved consistency of stools; prevention of constipation	Dietary fiber, flaxseed oil	Baked flaxseed	53 constipated patients with T2D with BMI 20.5–48.9 kg/m2; 12-week intervention; 10 g of flaxseed pre-mixed in cookies twice per day or placebo cookies for 12 weeks	Significantly improved constipation symptoms, particularly stool consistency [39]
		Flaxseed oil	50 constipated patients; 4-week intervention; intervention groups: the mineral oil group, the olive oil group, and the flaxseed oil group The initial oil dose was 4 mL/day, and adjustments during the follow-up could be made as needed. The average consumption of flaxseed oil was 6.9 ± 2.7 mL per day	The Rome III score improved significantly in patients receiving mineral oil (10.5 ± 5.0 to 4.1 ± 4.0; p < 0.01), olive oil (10.3 ± 4.2 to 3.2 ± 3.8; p < 0.01), and flaxseed oil (9.6 ± 4.2 to 6.0 ± 5.1; p < 0.01), with no significant group-by-time interaction (p < 0.15). The scores of 5 from 6 constipation symptoms reduced similarly in the mineral oil and olive oil groups, whereas only the frequency of evacuation and the consistency of stools improved in the flaxseed oil group [41]
Increased fecal fat excretion; prevention of being overweight and of obesity	Soluble dietary fiber	Flaxseed fiber drink, flaxseed fiber bread	17 participants; one-week intervention; intervention groups: a diet with flaxseed fiber drink or with flaxseed fiber bread Control group: low-fiber diet	Participants drinking flaxseed fiber drinks excreted 4.96 ± 0.31 g/d of fat, as compared to only 3.20 ± 0.33 g fat/d with the control diet, corresponding to a 55% increase. Participants eating flaxseed fiber bread eliminated 3.76 ± 0.31 g/d of fat with feces (p < 0.001) [42]
Reduction in mental fatigue	α-linolenic acid	Uncooked ground flaxseed	72 children and adolescents with a BMI > 25 kg/m2; 4-week intervention; intervention group: 20 g of flaxseed daily Control group: 25 g of puffed wheat daily	Significant reduction in mental fatigue in the group consuming flaxseed [44]
Reduction in or elimination of depression symptoms	α-linolenic acid	Flaxseed oil	60 depressed women; 10-week intervention with a control group; intervention group: 1000 mg of flaxseed oil capsule twice a day	Increase in serum BDNF concentration (1.12 ± 0.6 pg/mL vs. 0.2 ± 0.56 pg/mL; p < 0.001) and decrease in total BDI-II score (−16.62 ± 7.03 vs. −8.45 ± 7.8; p < 0.001) in the intervention group [45]
Improvement in skin condition	α-linolenic acid	Flaxseed oil	26 women with sensitive skin; 12-week intervention; intervention group: 4 capsules of flaxseed oil (555,32 mg/capsule) per day Control group: 4 capsules of safflower oil (560 mg/capsule) per day	Significant decrease in sensitivity, skin roughness, scaling, and transepidermal water loss, while epidermal hydration and smoothness were increased in the intervention group [46]
Improvement in wound healing	Omega-3 fatty acids	Flaxseed oil	60 participants with grade 3 diabetic foot syndrome; 12-week intervention; intervention group: 1000 mg of omega-3 fatty acids from flaxseed oil twice a day	Significant reduction in the length and depth of ulcers in the intervention group [47]

LDL-C—low-density lipoprotein cholesterol; TG—triglicerydes; HDL-C—high-density lipoprotein cholesterol; BMI—body mass index; SBP—systolic blood pressure; DBP—diastolic blood pressure; HOMA-IR—homeostatic model assessment for insulin resistance; ENL—enterolactone; hs-CRP—high-sensitive C-reactive protein; sVCAM-1—soluble vascular cell adhesion molecule type; NO—nitrogen oxide; PCR—polymerase chain reaction; T2D—type 2 diabetes; BDNF—brain-derived neurotrophic factor; BDI-II—Beck Depression Inventory-II.