Flaxseed

What Is Flaxseed?

Flaxseed, or linseed, is the seed of Linum usitatissimum, one of the oldest cultivated plants. The stem gives linen fibre and the seed gives linseed oil, and the seed itself is eaten as a food and taken as a medicine ^{15Reference 15Morin · 2016Linum usitatissimum Linnaeus — species description, habitat and distribution — floraView study →}.

Flax has been cultivated since prehistoric times, and its exact origin is uncertain ^{16,17Reference 16Liu et al. · 2008Linum usitatissimum Linnaeus — species description and distribution — floraView study →Reference 17AbdullaLinum usitatissimum LinnView study →}. It is now grown across the temperate world as a field crop.

The seed is rich in gel-forming mucilage, in lignans and in the omega-3 fatty acid alpha-linolenic acid ^{4,12,13Reference 4Khalesi et al. · 2015Meta-analysisFlaxseed consumption may reduce blood pressure: a systematic review and meta-analysis of controlled trialsView study →Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →Reference 13Kuijsten et al. · 2005RCTThe relative bioavailability of enterolignans in humans is enhanced by milling and crushing of flaxseed — randomised crossover trial, n=12View study →}. Dozens of human trials have tested the ground seed for cholesterol, blood pressure, blood sugar, weight and bowel function, with small but consistent effects on cholesterol and blood pressure ^{1,2,3,4,5,6,7Reference 1Pan et al. · 2009Meta-analysisMeta-analysis of the effects of flaxseed interventions on blood lipidsView study →Reference 2Rodriguez-Leyva et al. · 2013Potent antihypertensive action of dietary flaxseed in hypertensive patients (FLAX-PAD)View study →Reference 3Ursoniu et al. · 2016Meta-analysisEffects of flaxseed supplements on blood pressure: a systematic review and meta-analysis of controlled clinical trialsView study →Reference 4Khalesi et al. · 2015Meta-analysisFlaxseed consumption may reduce blood pressure: a systematic review and meta-analysis of controlled trialsView study →Reference 5Mohammadi-Sartang et al. · 2017Meta-analysisThe effect of flaxseed supplementation on body weight and body composition: a systematic review and meta-analysis of 45 randomised placebo-controlled trialsView study →Reference 6Musazadeh et al. · 2024Meta-analysisEffects of flaxseed supplementation on inflammatory biomarkers: a GRADE-assessed systematic review and meta-analysis of randomised controlled trialsView study →Reference 7Xi et al. · 2023Meta-analysisFlaxseed supplementation significantly reduces hemoglobin A1c in patients with type 2 diabetes mellitus: a systematic review and meta-analysisView study →}.

Flax oil and the ground seed are used differently. The oil carries the fatty acids but not the fibre or lignans.

How Is Flaxseed Used?

Flaxseed is taken as the seed itself, whole, crushed or ground, and stirred into water, cereal, yoghurt or baked food.

• Ground seed (flaxseed meal) — about 30 g a day in most cholesterol and blood-pressure trials ^{1,2Reference 1Pan et al. · 2009Meta-analysisMeta-analysis of the effects of flaxseed interventions on blood lipidsView study →Reference 2Rodriguez-Leyva et al. · 2013Potent antihypertensive action of dietary flaxseed in hypertensive patients (FLAX-PAD)View study →}.
• Whole or bruised seed — 10–15 g with a glass of water two or three times a day, as a bulk laxative ^{12Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →}.
• Soaked seed — 5–10 g soaked in water to release the mucilage, as a soothing drink for mild digestive discomfort ^{12Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →}.
• Lignan extracts — concentrated seed lignans, used in some trials ^{1,8Reference 1Pan et al. · 2009Meta-analysisMeta-analysis of the effects of flaxseed interventions on blood lipidsView study →Reference 8Pan et al. · 2007RCTEffects of a flaxseed-derived lignan supplement in type 2 diabetic patients: a randomised, double-blind, cross-over trialView study →}.
• Flax oil — pressed from the seed and used as a culinary source of alpha-linolenic acid.
• Poultice — warm ground seed applied to the skin.

Grinding or crushing the seed releases much more of its lignans than swallowing it whole ^{13Reference 13Kuijsten et al. · 2005RCTThe relative bioavailability of enterolignans in humans is enhanced by milling and crushing of flaxseed — randomised crossover trial, n=12View study →}. The seed swells as it absorbs water, so it is always taken with plenty of fluid ^{12Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →}.

Traditional Uses

Western Herbal Medicine

Flaxseed is a long-standing demulcent and bulk laxative. The mucilaginous seed, or a drink made by soaking it, was taken to soothe irritated digestive and urinary membranes and to ease constipation.

A warm poultice of ground seed was a standard household remedy for boils, skin inflammation and chest complaints.

The EU recognises the soaked seed as a traditional demulcent for mild digestive discomfort, and the whole seed as a laxative for habitual constipation ^{12Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →}.

Indications

• High total and LDL cholesterol [ground seed, lignan extract]
• Mild high blood pressure [milled seed]
• Habitual constipation [whole or ground seed; EU monograph]
• Mild digestive discomfort [soaked seed; traditional EU use]
• Raised blood sugar in type 2 diabetes [ground seed, lignan extract]
• Metabolic syndrome [ground seed]
• Boils and skin inflammation [warm seed poultice; Western folk use]
• Menopausal hot flashes [lignan-rich seed] ⚠Caution: A phase III placebo-controlled trial of a flaxseed bar providing 410 mg of lignans a day found no benefit over placebo ¹¹.

Botany

Flax is a slender annual herb in the flax family (Linaceae), growing 20–120 cm tall ^{15,16Reference 15Morin · 2016Linum usitatissimum Linnaeus — species description, habitat and distribution — floraView study →Reference 16Liu et al. · 2008Linum usitatissimum Linnaeus — species description and distribution — floraView study →}. Its stems are erect and branch mainly near the top or the base ^{15,16Reference 15Morin · 2016Linum usitatissimum Linnaeus — species description, habitat and distribution — floraView study →Reference 16Liu et al. · 2008Linum usitatissimum Linnaeus — species description and distribution — floraView study →}.

The leaves are narrow, linear to lance-shaped, and 1–4 cm long ^{15,16Reference 15Morin · 2016Linum usitatissimum Linnaeus — species description, habitat and distribution — floraView study →Reference 16Liu et al. · 2008Linum usitatissimum Linnaeus — species description and distribution — floraView study →}. The flowers are usually blue and occasionally white, with obovate petals 0.8–1.5 cm long ^{15,16Reference 15Morin · 2016Linum usitatissimum Linnaeus — species description, habitat and distribution — floraView study →Reference 16Liu et al. · 2008Linum usitatissimum Linnaeus — species description and distribution — floraView study →}.

Each flower ripens into a rounded capsule 6–10 mm across, holding up to ten seeds ^{15,16Reference 15Morin · 2016Linum usitatissimum Linnaeus — species description, habitat and distribution — floraView study →Reference 16Liu et al. · 2008Linum usitatissimum Linnaeus — species description and distribution — floraView study →}. The seeds are flattened, oblong, shiny and brown, about 3.5–6 mm long ^{15,16,17Reference 15Morin · 2016Linum usitatissimum Linnaeus — species description, habitat and distribution — floraView study →Reference 16Liu et al. · 2008Linum usitatissimum Linnaeus — species description and distribution — floraView study →Reference 17AbdullaLinum usitatissimum LinnView study →}.

The seed coat carries a layer of mucilage that swells in water ^{12,15Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →Reference 15Morin · 2016Linum usitatissimum Linnaeus — species description, habitat and distribution — floraView study →}.

Distribution

Flax is grown across Europe, Asia and the Americas, from the plains up to about 1,900 m in Pakistan ^{16,17Reference 16Liu et al. · 2008Linum usitatissimum Linnaeus — species description and distribution — floraView study →Reference 17AbdullaLinum usitatissimum LinnView study →}. Its original homeland is uncertain, and may lie in the Mediterranean region and western Asia ^{16Reference 16Liu et al. · 2008Linum usitatissimum Linnaeus — species description and distribution — floraView study →}.

The cultivated plant has escaped and naturalised in many places. In North America it turns up on roadsides, fields and disturbed ground ^{15Reference 15Morin · 2016Linum usitatissimum Linnaeus — species description, habitat and distribution — floraView study →}.

Growing Conditions

Cultivation snapshot for Flaxseed

Lifeannual

ZoneUSDA 3–9 as a sown field crop; it wants a cool temperate growing season.

• Full sun on deep, fertile, well-drained loam, sown direct in spring — it is a broadacre crop rather than a garden plant.
• Fibre and seed varieties are the same species bred two ways: fibre flax is grown tall, dense and unbranched for linen; oilseed varieties are shorter, branchier and higher-yielding for seed.

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Pharmacology & Research

Flaxseed has been tested in dozens of randomised controlled trials, pooled in meta-analyses of blood lipids, blood pressure, body weight, inflammation and blood sugar ^{1,3,4,5,6,7Reference 1Pan et al. · 2009Meta-analysisMeta-analysis of the effects of flaxseed interventions on blood lipidsView study →Reference 3Ursoniu et al. · 2016Meta-analysisEffects of flaxseed supplements on blood pressure: a systematic review and meta-analysis of controlled clinical trialsView study →Reference 4Khalesi et al. · 2015Meta-analysisFlaxseed consumption may reduce blood pressure: a systematic review and meta-analysis of controlled trialsView study →Reference 5Mohammadi-Sartang et al. · 2017Meta-analysisThe effect of flaxseed supplementation on body weight and body composition: a systematic review and meta-analysis of 45 randomised placebo-controlled trialsView study →Reference 6Musazadeh et al. · 2024Meta-analysisEffects of flaxseed supplementation on inflammatory biomarkers: a GRADE-assessed systematic review and meta-analysis of randomised controlled trialsView study →Reference 7Xi et al. · 2023Meta-analysisFlaxseed supplementation significantly reduces hemoglobin A1c in patients with type 2 diabetes mellitus: a systematic review and meta-analysisView study →}. It is also approved in the EU as a bulk laxative ^{12Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →}.

The clearest findings are a small fall in total and LDL cholesterol and a small fall in blood pressure ^{1,2,3,4Reference 1Pan et al. · 2009Meta-analysisMeta-analysis of the effects of flaxseed interventions on blood lipidsView study →Reference 2Rodriguez-Leyva et al. · 2013Potent antihypertensive action of dietary flaxseed in hypertensive patients (FLAX-PAD)View study →Reference 3Ursoniu et al. · 2016Meta-analysisEffects of flaxseed supplements on blood pressure: a systematic review and meta-analysis of controlled clinical trialsView study →Reference 4Khalesi et al. · 2015Meta-analysisFlaxseed consumption may reduce blood pressure: a systematic review and meta-analysis of controlled trialsView study →}. In the lipid meta-analysis, the whole seed and lignan supplements lowered cholesterol and flaxseed oil did not ^{1Reference 1Pan et al. · 2009Meta-analysisMeta-analysis of the effects of flaxseed interventions on blood lipidsView study →}.

Most positive trials used around 30 g a day of milled seed for twelve weeks or more ^{2,5Reference 2Rodriguez-Leyva et al. · 2013Potent antihypertensive action of dietary flaxseed in hypertensive patients (FLAX-PAD)View study →Reference 5Mohammadi-Sartang et al. · 2017Meta-analysisThe effect of flaxseed supplementation on body weight and body composition: a systematic review and meta-analysis of 45 randomised placebo-controlled trialsView study →}. A phase III trial for menopausal hot flashes found no benefit ^{11Reference 11Pruthi et al. · 2012RCTA phase III, randomised, placebo-controlled, double-blind trial of flaxseed for the treatment of hot flashes (NCCTG N08C7)View study →}.

1. Cholesterol

A meta-analysis of 28 randomised controlled trials found that flaxseed lowered total cholesterol by about 0.10 mmol/L and LDL by about 0.08 mmol/L overall ^{1Reference 1Pan et al. · 2009Meta-analysisMeta-analysis of the effects of flaxseed interventions on blood lipidsView study →}.

The reductions were significant for whole flaxseed (total −0.21, LDL −0.16 mmol/L) and for lignan supplements (total −0.28, LDL −0.16 mmol/L), but not for flaxseed oil ^{1Reference 1Pan et al. · 2009Meta-analysisMeta-analysis of the effects of flaxseed interventions on blood lipidsView study →}.

Effects were larger in women, particularly after menopause, in people with higher starting cholesterol, and in better-designed trials. HDL and triglycerides did not change ^{1Reference 1Pan et al. · 2009Meta-analysisMeta-analysis of the effects of flaxseed interventions on blood lipidsView study →}.

In a 12-week trial in constipated people with type 2 diabetes, cookies containing 10 g of flaxseed twice a day lowered total and LDL cholesterol compared with placebo ^{10Reference 10Soltanian et al. · 2019Effect of flaxseed or psyllium vs. placebo on management of constipation, weight, glycemia and lipids in constipated patients with type 2 diabetesView study →}.

Gap: the effects are small, and depend on the seed or lignan form rather than the oil.

2. Blood Pressure

Two meta-analyses found a small fall in blood pressure.

One, of 15 trials with 1,302 participants, found systolic pressure down 2.85 mmHg and diastolic down 2.39 mmHg. Trials of 12 weeks or more showed larger falls, and systolic pressure fell with flaxseed powder but not with oil or lignan extract ^{3Reference 3Ursoniu et al. · 2016Meta-analysisEffects of flaxseed supplements on blood pressure: a systematic review and meta-analysis of controlled clinical trialsView study →}.

The other, of 11 studies, found systolic pressure down 1.77 mmHg and diastolic down 1.58 mmHg. Diastolic pressure fell further with whole flaxseed and with 12 weeks or more of use ^{4Reference 4Khalesi et al. · 2015Meta-analysisFlaxseed consumption may reduce blood pressure: a systematic review and meta-analysis of controlled trialsView study →}.

In the FLAX-PAD trial, 110 people with peripheral artery disease ate foods containing 30 g of milled flaxseed or placebo every day for six months. Systolic pressure was about 10 mmHg lower and diastolic about 7 mmHg lower with flaxseed ^{2Reference 2Rodriguez-Leyva et al. · 2013Potent antihypertensive action of dietary flaxseed in hypertensive patients (FLAX-PAD)View study →}.

In those who started with systolic pressure of 140 mmHg or more, the falls were 15 and 7 mmHg. Blood levels of alpha-linolenic acid correlated with both pressures, and lignan levels with the change in diastolic pressure ^{2Reference 2Rodriguez-Leyva et al. · 2013Potent antihypertensive action of dietary flaxseed in hypertensive patients (FLAX-PAD)View study →}.

Gap: the pooled effect (about 2–3 mmHg) is far smaller than the single FLAX-PAD result (about 10 mmHg), and the large effect has not been replicated in newly diagnosed, untreated hypertension.

3. Body Weight & Composition

A meta-analysis of 45 placebo-controlled trials found small reductions in body weight (−0.99 kg), BMI (−0.30 kg/m²) and waist circumference (−0.80 cm) ^{5Reference 5Mohammadi-Sartang et al. · 2017Meta-analysisThe effect of flaxseed supplementation on body weight and body composition: a systematic review and meta-analysis of 45 randomised placebo-controlled trialsView study →}.

The benefit showed up with whole flaxseed at 30 g a day or more, with 12 weeks or more of use, and in people with a BMI of 27 or higher ^{5Reference 5Mohammadi-Sartang et al. · 2017Meta-analysisThe effect of flaxseed supplementation on body weight and body composition: a systematic review and meta-analysis of 45 randomised placebo-controlled trialsView study →}.

The reductions are small, and the trials varied widely.

4. Anti-Inflammatory

A GRADE-assessed meta-analysis of 54 trials with 3,000 participants found that flaxseed lowered C-reactive protein (standardised mean difference −0.46) and interleukin-6 (−0.64), but did not change TNF-α ^{6Reference 6Musazadeh et al. · 2024Meta-analysisEffects of flaxseed supplementation on inflammatory biomarkers: a GRADE-assessed systematic review and meta-analysis of randomised controlled trialsView study →}.

The trials varied a great deal (I² above 80%), and these are blood markers rather than clinical outcomes ^{6Reference 6Musazadeh et al. · 2024Meta-analysisEffects of flaxseed supplementation on inflammatory biomarkers: a GRADE-assessed systematic review and meta-analysis of randomised controlled trialsView study →}.

5. Glycemic Control

A meta-analysis of 13 trials in type 2 diabetes found that flaxseed lowered HbA1c, most clearly in people whose HbA1c was 7.0% or higher ^{7Reference 7Xi et al. · 2023Meta-analysisFlaxseed supplementation significantly reduces hemoglobin A1c in patients with type 2 diabetes mellitus: a systematic review and meta-analysisView study →}.

Overall, fasting glucose and insulin resistance did not change. In the subgroups with poorer control (fasting glucose of 8.0 mmol/L or more, or HbA1c of 7.0% or more), fasting glucose did fall ^{7Reference 7Xi et al. · 2023Meta-analysisFlaxseed supplementation significantly reduces hemoglobin A1c in patients with type 2 diabetes mellitus: a systematic review and meta-analysisView study →}.

In a double-blind crossover trial in 68 people with type 2 diabetes, a flaxseed-derived lignan supplement (360 mg a day for 12 weeks) lowered HbA1c slightly compared with placebo, without changing fasting glucose, insulin or lipids ^{8Reference 8Pan et al. · 2007RCTEffects of a flaxseed-derived lignan supplement in type 2 diabetic patients: a randomised, double-blind, cross-over trialView study →}.

6. Constipation

The seed-coat mucilage swells with water, softening the stool and adding bulk ^{12Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →}.

In a 4-week trial in 90 adults with functional constipation, 50 g a day of flaxseed flour cut the median Wexner constipation score from 14 to 6.5 and raised weekly bowel movements from 2 to 7. It was somewhat more effective than lactulose at increasing bowel frequency ^{9Reference 9Sun et al. · 2020Effects of flaxseed supplementation on functional constipation and quality of life in a Chinese populationView study →}.

In a 12-week single-blind trial in 77 constipated people with type 2 diabetes, 10 g of flaxseed twice a day in cookies improved constipation symptoms and stool consistency compared with placebo ^{10Reference 10Soltanian et al. · 2019Effect of flaxseed or psyllium vs. placebo on management of constipation, weight, glycemia and lipids in constipated patients with type 2 diabetesView study →}.

The EU recognises linseed as a well-established treatment for habitual constipation ^{12Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →}.

7. Menopausal Symptoms

A phase III, randomised, placebo-controlled trial in 188 postmenopausal women tested a flaxseed bar providing 410 mg of lignans a day for six weeks. Hot-flash scores fell by 4.9 with flaxseed and 3.5 with placebo, a difference that was not significant (p = 0.29). Slightly more than a third of women in each group halved their hot-flash score ^{11Reference 11Pruthi et al. · 2012RCTA phase III, randomised, placebo-controlled, double-blind trial of flaxseed for the treatment of hot flashes (NCCTG N08C7)View study →}.

Flaxseed lignans are converted by gut bacteria into enterodiol and enterolactone ^{13Reference 13Kuijsten et al. · 2005RCTThe relative bioavailability of enterolignans in humans is enhanced by milling and crushing of flaxseed — randomised crossover trial, n=12View study →}, and the EU notes that linseed may have an oestrogenic effect ^{12Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →}.

Gap: the best-designed trial found no benefit.

Mechanisms

Flaxseed’s effects come from three parts of the seed. The mucilage in the seed coat swells with water into a gel, which bulks and softens the stool ^{12Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →}. The lignans are converted by gut bacteria into the enterolignans enterodiol and enterolactone ^{13Reference 13Kuijsten et al. · 2005RCTThe relative bioavailability of enterolignans in humans is enhanced by milling and crushing of flaxseed — randomised crossover trial, n=12View study →}.

The oil in the kernel is rich in alpha-linolenic acid, a plant omega-3 fatty acid. In the FLAX-PAD trial, blood levels of alpha-linolenic acid tracked the fall in blood pressure ^{2Reference 2Rodriguez-Leyva et al. · 2013Potent antihypertensive action of dietary flaxseed in hypertensive patients (FLAX-PAD)View study →}.

Clinical Trials

Flaxseed has been tested in many completed human trials and several meta-analyses across lipids, blood pressure, blood sugar, weight and inflammation ^{1,3,4,5,6,7Reference 1Pan et al. · 2009Meta-analysisMeta-analysis of the effects of flaxseed interventions on blood lipidsView study →Reference 3Ursoniu et al. · 2016Meta-analysisEffects of flaxseed supplements on blood pressure: a systematic review and meta-analysis of controlled clinical trialsView study →Reference 4Khalesi et al. · 2015Meta-analysisFlaxseed consumption may reduce blood pressure: a systematic review and meta-analysis of controlled trialsView study →Reference 5Mohammadi-Sartang et al. · 2017Meta-analysisThe effect of flaxseed supplementation on body weight and body composition: a systematic review and meta-analysis of 45 randomised placebo-controlled trialsView study →Reference 6Musazadeh et al. · 2024Meta-analysisEffects of flaxseed supplementation on inflammatory biomarkers: a GRADE-assessed systematic review and meta-analysis of randomised controlled trialsView study →Reference 7Xi et al. · 2023Meta-analysisFlaxseed supplementation significantly reduces hemoglobin A1c in patients with type 2 diabetes mellitus: a systematic review and meta-analysisView study →}. A registered trial of flaxseed in newly diagnosed hypertension (NCT01952340) was terminated.

Last checked: September 2026.

Phytochemistry

Nearly a quarter of the seed is bulk material, including 3–6% mucilage and 4–7% dietary fibre ^{12Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →}. The mucilage sits in the seed coat and forms a gel in water.

Flaxseed is one of the richest dietary sources of lignans ^{13Reference 13Kuijsten et al. · 2005RCTThe relative bioavailability of enterolignans in humans is enhanced by milling and crushing of flaxseed — randomised crossover trial, n=12View study →}. The main one is secoisolariciresinol diglucoside, and the seed also contains matairesinol. Gut bacteria convert the plant lignans into enterodiol and enterolactone ^{13Reference 13Kuijsten et al. · 2005RCTThe relative bioavailability of enterolignans in humans is enhanced by milling and crushing of flaxseed — randomised crossover trial, n=12View study →}.

The oil is rich in alpha-linolenic acid, a plant omega-3 fatty acid ^{4Reference 4Khalesi et al. · 2015Meta-analysisFlaxseed consumption may reduce blood pressure: a systematic review and meta-analysis of controlled trialsView study →}.

The seed also contains cyanogenic glycosides, mainly linustatin and neolinustatin, with smaller amounts of linamarin ^{14Reference 14EFSA Panel on Contaminants in the Food C et al. · 2019Evaluation of the health risks related to the presence of cyanogenic glycosides in foods other than raw apricot kernels — regulatory risk assessmentView study →}.

In the lipid meta-analysis, the whole seed and lignan supplements lowered cholesterol and the oil did not ^{1Reference 1Pan et al. · 2009Meta-analysisMeta-analysis of the effects of flaxseed interventions on blood lipidsView study →}.

Constituent Summary

Amounts are for the whole seed.

Dosage

Most trials used about 30 g a day of milled seed for twelve weeks or more, or a lignan supplement ^{1,2,5Reference 1Pan et al. · 2009Meta-analysisMeta-analysis of the effects of flaxseed interventions on blood lipidsView study →Reference 2Rodriguez-Leyva et al. · 2013Potent antihypertensive action of dietary flaxseed in hypertensive patients (FLAX-PAD)View study →Reference 5Mohammadi-Sartang et al. · 2017Meta-analysisThe effect of flaxseed supplementation on body weight and body composition: a systematic review and meta-analysis of 45 randomised placebo-controlled trialsView study →}. For constipation, the EU dose is 10–15 g of seed with 150 mL of fluid two to three times a day ^{12Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →}.

Effects build over weeks rather than days. Take with plenty of fluid.

Traditional Dosage

Safety & Pregnancy

Flaxseed is a staple food and is well tolerated. Its cautions come from how the seed swells in water and from its fibre and lignans.

Full Safety Detail

Swelling and obstruction. The mucilage swells as it takes up water. Taken without enough fluid, the seed can block the throat or oesophagus and cause choking, or cause intestinal obstruction. Chest pain, vomiting or difficulty swallowing or breathing after taking it needs urgent medical attention ^{12Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →}.

Contraindications. The EU monograph lists bowel obstruction or paralysis, abnormal narrowing of the gut, megacolon, diseases of the oesophagus, and difficulty swallowing. As a laxative, it should not be used for a sudden change in bowel habit lasting more than two weeks, for undiagnosed rectal bleeding, or when a laxative has failed to work ^{12Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →}.

Other medicines. Bulk laxatives such as linseed can delay the absorption of medicines taken at the same time, so the seed is taken at least half an hour to an hour apart from them. Because of the risk of obstruction, it is used with opioids, loperamide and other drugs that slow the gut only under medical supervision ^{12Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →}.

Oestrogenic effect. Studies in healthy women suggest long-term use may have an oestrogenic effect, so the EU does not recommend it for women with hormone-dependent tumours ^{12Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →}.

Cyanogenic glycosides. The seed contains cyanogenic glycosides. Cyanide is released from ground linseed more slowly and less completely than from cassava or bitter almonds, and food regulators have found no reports of poisoning from eating linseed ^{14Reference 14EFSA Panel on Contaminants in the Food C et al. · 2019Evaluation of the health risks related to the presence of cyanogenic glycosides in foods other than raw apricot kernels — regulatory risk assessmentView study →}.

Side effects. Bloating and wind are common. Allergic reactions, including anaphylaxis-like reactions, occur very rarely ^{12Reference 12Committee on Herbal Medicinal Products ( · 2015Systematic reviewEuropean Union herbal monograph on Linum usitatissimum L., semen (EMA/HMPC/377675/2014), final, first systematic review — regulatory monographView study →}.

References

1. Pan, A., Yu, D., Demark-Wahnefried, W., Franco, O. H., & Lin, X. (2009). Meta-analysis of the effects of flaxseed interventions on blood lipids. American Journal of Clinical Nutrition. https://pubmed.ncbi.nlm.nih.gov/19515737/
2. Rodriguez-Leyva, D., Weighell, W., Edel, A. L., et al. (2013). Potent antihypertensive action of dietary flaxseed in hypertensive patients (FLAX-PAD). Hypertension. https://pubmed.ncbi.nlm.nih.gov/24126178/
3. Ursoniu, S., Sahebkar, A., Andrica, F., Serban, C., & Banach, M. (2016). Effects of flaxseed supplements on blood pressure: a systematic review and meta-analysis of controlled clinical trials. Clinical Nutrition. https://pubmed.ncbi.nlm.nih.gov/26071633/
4. Khalesi, S., Irwin, C., & Schubert, M. (2015). Flaxseed consumption may reduce blood pressure: a systematic review and meta-analysis of controlled trials. Journal of Nutrition. https://pubmed.ncbi.nlm.nih.gov/25740909/
5. Mohammadi-Sartang, M., Mazloom, Z., Raeisi-Dehkordi, H., et al. (2017). The effect of flaxseed supplementation on body weight and body composition: a systematic review and meta-analysis of 45 randomised placebo-controlled trials. Obesity Reviews. https://pubmed.ncbi.nlm.nih.gov/28635182/
6. Musazadeh, V., Morovatshoar, R., Kavyani, Z., Vajdi, M., & Askari, G. (2024). Effects of flaxseed supplementation on inflammatory biomarkers: a GRADE-assessed systematic review and meta-analysis of randomised controlled trials. Prostaglandins & Other Lipid Mediators. https://pubmed.ncbi.nlm.nih.gov/38971216/
7. Xi, H., Zhou, W., Sohaib, M., et al. (2023). Flaxseed supplementation significantly reduces hemoglobin A1c in patients with type 2 diabetes mellitus: a systematic review and meta-analysis. Nutrition Research. https://pubmed.ncbi.nlm.nih.gov/36640581/
8. Pan, A., Sun, J., Chen, Y., et al. (2007). Effects of a flaxseed-derived lignan supplement in type 2 diabetic patients: a randomised, double-blind, cross-over trial. PLOS ONE. https://pubmed.ncbi.nlm.nih.gov/17987126/
9. Sun, J., Bai, H., Ma, J., et al. (2020). Effects of flaxseed supplementation on functional constipation and quality of life in a Chinese population. Asia Pacific Journal of Clinical Nutrition. https://pubmed.ncbi.nlm.nih.gov/32229443/
10. Soltanian, N., & Janghorbani, M. (2019). Effect of flaxseed or psyllium vs. placebo on management of constipation, weight, glycemia and lipids in constipated patients with type 2 diabetes. Clinical Nutrition ESPEN. https://pubmed.ncbi.nlm.nih.gov/30661699/
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