Flax is one of the oldest plants people have used. Archaeologists found spun, dyed and knotted wild flax fibers in a cave in Georgia, in layers about 30,000 years old, long before farming began. Carl Linnaeus gave the crop the species name Linum usitatissimum in 1753, and usitatissimum means “most useful.” Linen cloth comes from the stem, and the seed is sold as flaxseed or, in Britain, linseed.
One tablespoon (10 g) of whole flaxseed has 55 calories, 2.8 g of fiber and about 2.35 g of alpha-linolenic acid (ALA), the plant omega-3 fat, according to USDA data on this site. Per 100 g, flaxseed ranks first of 110 foods in our database for omega-3 fat and third of 109 for fiber. It also ranks first of 131 for vitamin B1 (thiamin). In one trial, blood levels of the fish omega-3s EPA and DHA did not rise significantly after months of flaxseed.
Flaxseed research mixes forms: whole seed, milled seed, flax oil and lignan extracts. Whole seeds can pass through the gut unbroken, and in one trial whole seed muffins did not raise blood ALA while milled seed did. Raw flaxseed also contains cyanogenic glycosides that release hydrogen cyanide when seeds are crushed, so food safety agencies set a daily amount for raw ground seed. Cards below say when a study tested oil or an extract instead of the seed.
Health benefits of flaxseed
The top findings from 31 studies, strongest evidence first
What the stars mean
- Strong. Several randomized trials, pooled in a meta-analysis, point the same way, or regulators (FDA or EFSA) have approved the claim.
- Moderate. Good randomized trials support it, but there are fewer of them, or their results vary.
- Limited. Small, short or single trials, or mixed results. Promising, but it needs confirmation.
Population and lab studies get no stars: they show a link or a mechanism, not proof.
How we rate evidence →- ★★Slightly lower blood pressureIn 33 trials of flaxseed products, the top number fell a little (by 3.2 mm Hg systolic). Another pooled analysis found a smaller drop (1.8 mm Hg systolic), and results differed widely between trials.
- ★★Slightly lower LDL, mixed in healthy peopleIn 62 trials, flaxseed supplements lowered LDL a little (by 4.2 mg/dL); in 28 trials, by only 0.08 mmol/L. In 14 trials, healthy people’s LDL and triglycerides rose, while people with abnormal blood fats improved.
- ★★Slightly lower fasting blood sugar with whole flaxseedIn 25 trials, whole flaxseed lowered fasting blood sugar a little (by 2.94 mg/dL), but flaxseed oil and lignan extract did not. In 13 type 2 diabetes trials, HbA1c (a three-month blood sugar average) fell, most clearly starting at 7.0% or higher, but fasting glucose did not.
- ★★Slightly lower body weightIn 45 trials, flaxseed supplements lowered body weight by 0.99 kg on average, and waist size by 0.80 cm. The effect showed in trials of whole flaxseed at 30 g a day or more and of 12 weeks or longer.
- ★★Mixed results for inflammation markersOne analysis of randomized trials found flaxseed lowered the inflammation markers hs-CRP and TNF-alpha, but not IL-6 or standard CRP. Another, of 17 trials, found no significant change in CRP (a drop of 0.25 mg/L, which could be chance).
All 31 studies, strongest evidence first
Flaxseed products lowered systolic blood pressure by 3.2 mmHg and diastolic by 2.6 mmHg in 33 trials
Meta-analysis of 33 randomized trials (2,427 people) of various flaxseed products. The drops were larger in trials of at least 30 g a day, in trials longer than 20 weeks, and in people with hypertension. Results differed widely from trial to trial.
Flaxseed supplements lowered LDL cholesterol by 4.2 mg/dL and triglycerides by 9.4 mg/dL in 62 trials
Meta-analysis of 62 randomized trials (3,772 people). Total cholesterol fell 5.4 mg/dL, and HDL did not change. The abstract does not separate seed from oil or other forms, and the authors call for larger trials.
Whole flaxseed lowered fasting blood sugar by about 3 mg/dL, but flaxseed oil and lignan extract did not
Meta-analysis of 25 randomized, placebo-controlled trials (30 treatment arms). Fasting glucose fell 2.94 mg/dL and an insulin resistance score (HOMA-IR) fell 0.49, while HbA1c, the three-month sugar average, did not change significantly. These effects appeared only in trials of whole flaxseed.
Flaxseed supplements lowered body weight by about 1 kg in 45 trials
Meta-analysis of 45 randomized, placebo-controlled trials. Weight fell 0.99 kg, BMI 0.30 and waist size 0.80 cm on average. The effect showed in trials of whole flaxseed at 30 g a day or more, trials of 12 weeks or longer, and people with a BMI of 27 or higher.
Flaxseed products lowered systolic blood pressure by 2.85 mmHg and diastolic by 2.39 mmHg, but lignan extract did nothing
Meta-analysis of 15 randomized trials (1,302 people). Flaxseed powder lowered systolic pressure by 1.81 mmHg, while oil and lignan extract did not. Diastolic pressure fell with powder and oil but not lignan extract, and drops were larger in trials of 12 weeks or more.
Flaxseed lowered blood pressure by 1.8 mmHg systolic and 1.6 mmHg diastolic, a slight drop
Meta-analysis of 11 studies (14 trials) in which people ate flaxseed or its extracts (oil, lignans, fiber) for 2 weeks or more. Whole seed gave a diastolic drop of 1.93 mmHg, and trials of 12 weeks or more a drop of 2.17 mmHg. The authors say flaxseed may lower blood pressure slightly.
Flaxseed lowered LDL cholesterol by 0.08 mmol/L, a very small drop that was larger for whole seed (0.16 mmol/L)
Meta-analysis of 28 trials of flaxseed and products made from it (oil, lignans). Total cholesterol fell 0.10 mmol/L overall and 0.21 mmol/L with whole flaxseed, but not with flaxseed oil. The range of results just touched zero. HDL and triglycerides did not change.
Flaxseed lowered HbA1c in people with type 2 diabetes, but not fasting glucose, weight or blood pressure overall
Meta-analysis of 13 randomized trials in type 2 diabetes. HbA1c, the three-month blood sugar average, fell most clearly in people whose starting HbA1c was 7.0% or higher. In subgroup analyses, whole flaxseed raised HDL and lowered total and LDL cholesterol. The authors say larger, better designed trials are needed.
Flaxseed lowered the inflammation marker hs-CRP and TNF-alpha, but not IL-6 or standard CRP
Meta-analysis of 32 articles on randomized trials in adults aged 18 to 70. Seed, oil and lignan products were pooled, and results depended on study design, product type, study quality, age and BMI. The IL-6 result turned significant when one study was removed.
Flaxseed products did not significantly change blood CRP in 17 trials
Meta-analysis of 17 randomized trials (1,256 people). CRP, a marker of inflammation, fell by 0.25 mg/L on average, too little to rule out chance (p = 0.074). Ground flaxseed, flaxseed oil and lignan extract each gave the same null result.
In healthy people, flaxseed raised LDL cholesterol and triglycerides, while in people with abnormal blood fats it lowered them
Meta-analysis of 14 randomized trials (1,107 people). In people with abnormal blood fats, flaxseed improved total cholesterol, LDL and triglycerides. In healthy people it raised HDL, LDL and triglycerides, although LDL improved in those with a BMI above 25.
Eating 30 g of milled flaxseed a day for 6 months lowered systolic blood pressure by about 10 mmHg in people with artery disease in the legs
The FlaxPAD trial: a double-blind, placebo-controlled trial in 110 people with peripheral artery disease, with the flaxseed baked into a variety of foods. Diastolic pressure was about 7 mmHg lower. In people starting at 140 mmHg or more, the drops were 15 mmHg systolic and 7 mmHg diastolic. This is one trial in one patient group.
In people with high blood pressure, flaxseed lowered central aortic pressure by 10 and 6 mmHg (systolic and diastolic)
Follow-up of 62 people from the FlaxPAD trial in peripheral artery disease, compared with placebo. Flaxseed did not change the augmentation index (a measure of artery stiffness) or heart function. Blood levels of certain oxylipins, fat-derived signaling molecules, tracked with pressure and may help explain the effect.
15 g of ground raw golden flaxseed before breakfast cut the 2-hour blood sugar response by 24% in men with type 2 diabetes
Randomized crossover trial in 19 men with type 2 diabetes, each tested with and without flaxseed. The peak glucose rise was 17% lower. This tested a single meal, so it does not show long-term blood sugar control.
10 g of flaxseed in cookies, twice a day for 12 weeks, eased constipation and lowered weight and blood sugar in people with type 2 diabetes
Single-blind randomized trial in 77 constipated people with type 2 diabetes, who got flaxseed, psyllium or placebo cookies. Both flaxseed and psyllium beat placebo for constipation symptoms, weight, fasting glucose and LDL, and flaxseed looked better than psyllium. No side effects were reported.
50 g a day of flaxseed flour for 4 weeks raised bowel movements from 2 to 7 a week in adults with constipation
Randomized trial in 90 adults with functional constipation, comparing flaxseed flour (60 people) with the laxative lactulose (30 people), not with placebo. Bowel movements per week went from 2 to 7 with flaxseed and from 2 to 6 with lactulose, and the constipation score fell from 14 to 6.5 with flaxseed and from 15 to 9 with lactulose.
16 g of flaxseed a day for 3 months went with lower glucose, total cholesterol and triglycerides in Mexican adults with type 2 diabetes
Parallel randomized trial in 166 adults with type 2 diabetes in Oaxaca, Mexico (82 on flaxseed, 84 controls). The abstract says little about the control diet or how the seed was eaten, so treat the size of the effect with caution.
50 g of flaxseed a day for 4 weeks lowered LDL cholesterol by up to 8% in healthy young adults
Small trial in healthy young adults who ate flaxseed for 4 weeks. Urinary lignan excretion rose more than fivefold and bowel movements per week rose 30%. Baking did not significantly reduce ALA in muffins with 25 g of flaxseed, and antioxidant status was not harmed.
Whole flaxseed muffins did not raise blood ALA, while milled flaxseed and flax oil did
Healthy adults ate muffins with 30 g of whole seed, 30 g of milled seed or flax oil (6 g of ALA) for up to 3 months. Blood ALA rose with milled seed and oil but not whole seed, and no group raised EPA or DHA. Compliance was a problem in the whole seed group.
Two tablespoons a day of whole or ground linseed for 4 weeks did not significantly improve IBS symptoms compared with none
Open randomized pilot in 40 people with irritable bowel syndrome, of whom 31 finished. Whole seed against ground seed gave P = 0.62, and neither beat no linseed at the 5% level. Stool frequency did not change. It was too small to show real differences.
A daily flaxseed bar for 6 weeks did not reduce hot flashes more than a placebo bar in postmenopausal women
Randomized, double-blind trial in 188 women; the bar gave 410 mg of lignans. Hot flash scores fell 4.9 with flaxseed and 3.5 with placebo (P = 0.29). Both groups reported abdominal distension, gas and diarrhea.
15 g of ground flaxseed a day for 7 weeks raised 2-hydroxyestrone, an estrogen breakdown product, in postmenopausal women
Randomized trial in 99 postmenopausal women in Toronto, with flaxseed compared with usual diet. 2-hydroxyestrone was 1.54 times higher, and enterolignans, markers of lignan from the gut, rose 516%. Of 14 hormones measured, the other effects were not significant. It measured hormones, not breast cancer.
31.5 g of ground flax with a glucose drink lowered the 2-hour blood sugar rise, but less than chia did
Randomized crossover study in 15 healthy adults given 50 g of glucose alone, or with 25 g of ground Salba chia or 31.5 g of flax. Flax lowered the blood sugar area under the curve by 60.0 mmol/L (P = 0.014) and chia by 82.5 mmol/L, and chia also lowered appetite scores more.
Flaxseed fiber extract cut the blood fat rise after a meal by 18%, but whole flaxseed did not lower insulin as the fiber did
Double-blind crossover trial in 18 young men eating four matched meals: control, whole flaxseed, or flaxseed fiber at a low or high mucilage dose (a gel-forming fiber). The 18% was for the high-mucilage fiber. Later calorie intake did not differ. This tests fiber extracts, not the seed as eaten.
A flaxseed lignan extract at 600 mg a day lowered LDL cholesterol by about 22 to 24% in people with high cholesterol
This tested a lignan extract (SDG), not the seed. Double-blind, placebo-controlled trial in 55 people with high cholesterol for 8 weeks, at 300 or 600 mg a day. Fasting glucose also fell in the 600 mg group.
People who ate more ALA had a 10% lower risk of dying from any cause (risk ratio 0.90)
Meta-analysis of 41 cohort studies (1,197,564 people) of ALA, the plant omega-3 in flaxseed, from all foods such as oils and walnuts, not flaxseed alone. High ALA intake also went with lower cardiovascular death (0.92) but slightly higher cancer death (1.06). Cohorts cannot prove cause.
Higher ALA intake or blood levels went with a lower risk of cardiovascular disease (risk ratio 0.86)
Meta-analysis of 27 studies (251,049 people, 15,327 events) of ALA from all sources, not flaxseed alone. Dietary ALA gave 0.90, while the blood-level comparisons were not significant (0.80). Results varied a lot between studies.
Higher lignan intake went with a lower breast cancer risk in postmenopausal women, but not overall
Meta-analysis of 21 studies (11 cohort, 10 case-control) of lignans from the whole diet, not flaxseed alone. The risk estimate was 0.86 in postmenopausal women (13 studies) and 0.92 for all women, which was not significant. Blood and urine enterolactone showed no link.
Feeding mice 20% ground flaxseed lowered blood cholesterol by 19 to 22%
Mouse study in two models of high cholesterol on a Western-style diet, with whole ground flaxseed for 21 days. Liver cholesterol fell 32 to 66% depending on model and sex. The authors suspect less cholesterol absorption. Mouse results may not carry over to people.
Ground flaxseed in the diet inhibited plaque formation in the arteries of mice
Mice lacking the LDL receptor ate a high-cholesterol diet for 24 weeks, with or without 10% ground flaxseed. The flaxseed group had lower plasma cholesterol, more blood ALA and less artery plaque, along with lower markers of inflammation such as IL-6 and VCAM-1.
The flax lignan SDG reduced artery plaque by 73% in rabbits fed a high-cholesterol diet
Rabbit study of SDG, a lignan extracted from flaxseed, at 15 mg per kg of body weight a day, not the seed itself. At week 8, LDL cholesterol was 35% lower and HDL had risen by more than 140%.
Who should be careful with flaxseed
Most people can eat flaxseed freely. Take a little care if one of these applies:
- Large amounts of raw ground seed. Germany’s BfR expects no harm in adults from up to 15 to 20 g (about 2 to 3 level tablespoons) of raw ground linseed a day, advises no more than 4 g (about a teaspoon) for children aged 4 and over, and says young children should avoid it. Baking or cooking greatly lowers the cyanide risk, and the seed also carries cadmium, so the BfR caps adults at 20 g of linseed a day.
- Dry seeds and bowel problems. Case reports describe a linseed bezoar, a ball of seed, blocking the bowel, including in a teenager with anorexia. Medical guides advise taking flaxseed with plenty of water and avoiding it after a bowel obstruction or ileus. The risk is small for most people.
- Pregnancy and hormone-sensitive cancer. NIH’s NCCIH says some studies suggest flaxseed may be unsafe in pregnancy, though the evidence is not conclusive. Memorial Sloan Kettering advises people with estrogen receptor positive breast cancer to ask their doctor first.
How to choose, store and eat flaxseed
- Milled or ground: in a trial of muffins with 30 g of seed, blood ALA rose with milled seed but not with whole seed, and the FlaxPAD blood pressure trial used 30 g of milled seed a day.
- Whole: whole seeds release no hydrogen cyanide, but they may pass through undigested, and in a 40-person trial 2 tablespoons of whole or ground linseed did not differ significantly for IBS symptoms.
- Baked: heat evaporates hydrogen cyanide and switches off the enzyme that releases it, and baking did not significantly reduce ALA in muffins with 25 g of flaxseed.
Buy sealed, opaque packs and keep them airtight and cool. A flaxseed producer says whole seed lasts one to two years and milled seed up to a year, because grinding exposes more of the oil to air and light, and a bitter taste or fishy smell means it has gone off. Flaxseed oil is a different product: in one meta-analysis whole seed and lignan lowered cholesterol, but oil did not.
Sources
- Hydrocyanic acid and cadmium in linseeds. BfR (German Federal Institute for Risk Assessment), Communication 034/2026.
- EFSA Panel on Contaminants in the Food Chain. Evaluation of the health risks related to the presence of cyanogenic glycosides in foods other than raw apricot kernels. EFSA Journal. 2019.
- Abraham K, Buhrke T, Lampen A. Bioavailability of cyanide after consumption of a single meal of foods containing high levels of cyanogenic glycosides: a crossover study in humans. Arch Toxicol. 2016.
- Schlag S, Liese J, Veldhoen S. Acute abdomen with bilious vomiting: a linseed bezoar as a rare cause of an obstructive ileus in an anorexic adolescent. Klin Padiatr. 2021 (in German).
- Hardt M, Geisthövel W. Severe obstructive ileus caused by a linseed bezoar. Med Klin. 1986 (in German).
- Flaxseed. Boston University Family Medicine patient handout.
- Flaxseed (linseed): uses, side effects and dosage. RxList.
- Flaxseed and flaxseed oil. National Center for Complementary and Integrative Health (NIH). Updated February 2025.
- Flaxseed. Memorial Sloan Kettering Cancer Center, About Herbs.
- Healthy food trends: flaxseeds. MedlinePlus.
- How to store flaxseed. Bob’s Red Mill (a flaxseed producer).
- Austria JA, Richard MN, Chahine MN, et al. Bioavailability of alpha-linolenic acid in subjects after ingestion of three different forms of flaxseed. J Am Coll Nutr. 2008.
- Cunnane SC, Hamadeh MJ, Liede AC, et al. Nutritional attributes of traditional flaxseed in healthy young adults. Am J Clin Nutr. 1995.
- Cockerell KM, Watkins AS, Reeves LB, et al. Effects of linseeds on the symptoms of irritable bowel syndrome: a pilot randomised controlled trial. J Hum Nutr Diet. 2012.
- Pan A, Yu D, Demark-Wahnefried W, et al. Meta-analysis of the effects of flaxseed interventions on blood lipids. Am J Clin Nutr. 2009.
- Rodriguez-Leyva D, Weighell W, Edel AL, et al. Potent antihypertensive action of dietary flaxseed in hypertensive patients. Hypertension. 2013.
History of flaxseed
Flax was among the first plants people used, and fiber came before farming. Wild flax fibers from Dzudzuana Cave in the Caucasus foothills of Georgia show that hunter-gatherers made cords and spun, dyed and knotted flax fibers in layers dated to roughly 30,000 years ago.
Cultivated flax descends from a wild relative called pale flax, Linum bienne, and was first domesticated in the Fertile Crescent. Scientists still discuss how many times it happened: genetic work suggests the oil, fiber and winter-hardy types may come from more than one domestication event.
Linen cloth made flax valuable. Flax fabric fragments from Çatalhöyük in Turkey are about 9,000 years old. In Egypt, mummies were wrapped in linen and priests wore only linen as a sign of purity, and Sumerian priests wore it more than 4,000 years ago.
After the Roman Empire declined, flax production in Europe fell. Charlemagne revived the crop in the 8th century with laws promoting linen hygiene and linseed oil, and Flanders later became the main center of the European linen industry. Colonists brought flax to North America, where it flourished.
The word flax comes from Old English fleax. An older word, line, survives in linen, the cloth, and in linseed, the seed. Cheap synthetic fibers later reduced the commercial importance of flax as a fiber crop.
Sources
- Kvavadze E, Bar-Yosef O, Belfer-Cohen A, et al. 30,000-year-old wild flax fibers. Science. 2009.
- Fu YB. Population-based resequencing revealed an ancestral winter group of cultivated flax: implication for flax domestication processes. Ecol Evol. 2012.
- Flax. Wikipedia.
Frequently asked questions about flaxseed
Is flaxseed good for you?
It can be, but the evidence is modest. One tablespoon (10 g) of whole seed has 55 calories, 2.8 g of fiber and about 2.35 g of ALA, the plant omega-3 fat. In 33 trials, flaxseed products lowered blood pressure by about 3.2 over 2.6 mmHg, and 62 trials found LDL cholesterol 4.2 mg/dL lower. None of these findings reaches strong evidence, and raw ground seed has a daily limit for cyanide.
Is it better to eat flaxseed ground or whole?
Ground is better for most goals. In a trial of muffins with 30 g of seed, blood ALA rose with milled seed but not with whole seed, and MedlinePlus also says ground seed is easiest to digest. Whole seed releases no hydrogen cyanide, and in a 40-person IBS pilot whole and ground linseed did not differ significantly.
How much flaxseed should you eat a day?
No study sets an ideal amount. Trials used 15 g a day for 7 weeks, 16 g for 3 months, 30 g of milled seed for 6 months and 50 g for 4 weeks. The BfR expects no harm in adults from up to 15 to 20 g of raw ground seed a day, and baking lowers the cyanide risk. Blood pressure drops were larger in trials of 30 g or more, so talk to your clinician before eating that much.
Does flaxseed lower blood pressure?
A little, in trials. Three meta-analyses found drops of 1.6 to 3.2 mmHg, and the FlaxPAD trial of 30 g of milled seed a day found a drop of about 10 mmHg systolic in 110 people with artery disease in the legs. Results differed widely between trials, and lignan extract alone did not lower systolic pressure. Do not stop blood pressure medicine because of flaxseed.
Does flaxseed lower cholesterol?
Slightly, for some people. Across 62 trials LDL cholesterol was 4.2 mg/dL lower, and whole seed lowered it by 0.16 mmol/L in another meta-analysis while flax oil did not. A 14-trial review found flaxseed raised LDL in healthy people but lowered it in people with abnormal blood fats.
Does flaxseed help with constipation?
It looks helpful, though the trials are small. In 90 adults, 50 g a day of flaxseed flour raised bowel movements from 2 to 7 a week, but the comparison was a laxative, not a placebo. Flaxseed also eased constipation against placebo in 77 people with type 2 diabetes. Take it with plenty of water, and ask a doctor first if you have had a bowel obstruction.
Is flaxseed good for weight loss?
Only a little. In 45 trials flaxseed supplements lowered body weight by 0.99 kg on average, with the clearest effect from whole seed at 30 g a day or more over 12 weeks or longer in people with a BMI of 27 or higher. Flaxseed is not low in calories, with 55 per tablespoon, so the effect is modest.
Is flaxseed better than chia seeds?
Neither is clearly better. In a trial of 15 healthy adults, 31.5 g of ground flax lowered the blood sugar rise after glucose, but 25 g of ground chia lowered it more and also lowered appetite scores more. Per 100 g, flaxseed has 534 calories against 486 for chia on this site.