Flaxseed
Quick Facts
- What it is: Flaxseed is the seed of the flax plant, eaten ground, whole or as oil, and used mainly for constipation and heart health.
- Main uses: Constipation, High cholesterol, High blood pressure
- Best for: Adults wanting a food-based source of fibre, Mild constipation, A small added effect on cholesterol alongside medical care
- Active ingredients: Mucilage fibre, Alpha-linolenic acid (ALA), Lignans (SDG)
- Forms: Ground seed (meal), Whole seed, Oil, Capsules, Lignan (SDG) extract
- Time to effect: 12 to 72 hours for the laxative effect; 4 to 12 weeks or more for cholesterol and blood pressure.
- Side effects: Usually mild wind, bloating and loose stools; rarely gut blockage if taken with too little fluid.
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What is Flaxseed?
Flaxseed is the small brown or golden seed of the flax plant, Linum usitatissimum. It is also sold as linseed. People eat it whole, ground into meal, or pressed into oil.
It is used today for three main things. These are constipation, high cholesterol, and general heart health. American folk and Eclectic healers also mixed the crushed seed into warm poultices for the skin and chest.
Here is the short verdict on the evidence. Ground flaxseed works as a bulk laxative, and trials show small drops in cholesterol and blood pressure.
Other claims are weaker. Flaxseed for hot flushes has mostly failed in trials. Claims about cancer rest on lab and animal work, not on proof in people.
One point applies to this whole page. Long use in tradition is not proof that a remedy works, and it is not proof that it is safe.
How does Flaxseed work?
Most of what flaxseed does in people comes down to its fibre. The seed coat holds a sticky fibre called mucilage. It soaks up water in the gut, so stool gets bulkier and softer.
That same fibre is the likely reason cholesterol falls. In human studies, soluble fibre binds bile acids in the gut and carries them out. The body then pulls cholesterol from the blood to make more bile acids.
Flaxseed is also rich in ALA, a plant omega-3 fat. The body turns only a small part of ALA into the omega-3 fats found in fish oil. So flaxseed is not a direct swap for fish oil.
Flaxseed is the richest common food source of lignans. Gut bacteria change these into enterolactone and enterodiol. In cell studies these act weakly like oestrogen, the main female hormone, and can also block it.
What that hormone effect does in the human body is not settled. Trials in women have not shown clear relief of hot flushes. Treat the lignan story as an idea under test, not a known effect.
What forms does Flaxseed come in?
Whole seeds. These often pass through the gut undamaged, so you get less of the oil and lignans from them.
Ground flaxseed, also sold as flaxseed meal or flour. This is the form used in most trials.
Flaxseed oil, in bottles or capsules. The oil carries the ALA fat but almost no fibre and few lignans.
Lignan extracts, sold as SDG capsules.
Added to bread, cereal, bars and smoothies.
Flaxseed meal was once mixed with hot water as a poultice, a wet paste spread on the skin.
Where it comes from:
Flax is one of the oldest crops grown by people. It was used for linen cloth and for food in the Middle East and Egypt thousands of years ago.
American folk healers and Eclectic physicians in the 1800s knew it as linseed. They brewed the seed into a thick tea for coughs, sore throats and bladder irritation.
The hot linseed meal poultice was a standard item in those texts. It was laid on the chest for congestion, and on boils and sores to draw them out.
These writers also used the seed as a gentle laxative. That use is the one with the clearest support today.
Who should avoid Flaxseed?
- Never swallow flaxseed dry or with only a sip of liquid. Always take it with a full glass of water.
- Do not use if you have a blockage or narrowing anywhere in your gut, or a history of bowel obstruction.
- Do not use if you have a stricture (a narrowed food pipe) or trouble swallowing.
- Do not eat raw or unripe flaxseed in large amounts. These contain compounds that can release cyanide.
- Do not use if you have had an allergic reaction to flaxseed or linseed.
- Avoid flaxseed supplements, lignan extracts and oil capsules while pregnant or breastfeeding. Food amounts in bread or cereal are fine. Ask your midwife or doctor.
- Do not start flaxseed supplements if you take warfarin or another blood thinner without telling your doctor.
- Do not start it if you have had breast cancer or take tamoxifen without asking your oncologist first.
- Do not give flaxseed supplements to children without advice from a doctor.
When should you see a doctor?
Stop and get emergency care if you have swelling of the lips, face or throat, a widespread rash, or trouble breathing. These are signs of a serious allergic reaction.
Go to hospital if you get severe stomach pain, vomiting, a swollen belly, and no bowel movement or wind. This can mean a blocked gut.
See your doctor soon if constipation lasts more than a week, or if you have blood in your stool.
Also see your doctor if you feel dizzy or faint, which can mean your blood pressure has dropped too low.
Is Flaxseed legal where you live?
In the United States, the UK and the EU, flaxseed is an ordinary food. Ground seed, oil and capsules are sold as food supplements, not as medicines. No regulator has approved flaxseed to treat or prevent any disease.
Evidence grades and traditional-use labels are explained in our methodology. Nothing here is medical advice.
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