Flax
Quick Facts
- What it is: Flax is the oily, high-fibre seed of Linum usitatissimum, eaten as whole seed, meal or oil.
- Main uses: Constipation, High cholesterol, High blood pressure, Soothing a dry cough (traditional)
- Active ingredients: Alpha-linolenic acid (a plant omega-3 fat), Lignans, mainly SDG, Soluble and insoluble fibre, Mucilage
- Forms: Whole seed, Ground seed (flax meal), Food-grade oil, Oil capsules, Lignan (SDG) capsules, Linseed tea and poultices (traditional)
- Time to effect: Stool changes in 1 to 3 days; cholesterol and blood pressure changes take 4 to 24 weeks, if they come at all.
- Side effects: Usually just wind and bloating; blockage risk with too little water, and rare allergy.
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What is Flax?
What is flax?
Flax (Linum usitatissimum) is a crop grown across northern Europe. The seeds are eaten whole, ground, or pressed for oil. In Finland it is called pellava.
The seed is high in fibre and in alpha-linolenic acid, a plant omega-3 fat. It also holds lignans, plant compounds that act weakly like oestrogen (a female sex hormone). Linen cloth comes from the stem of the same plant.
The short verdict: ground flaxseed has fair human support for small drops in cholesterol and blood pressure, and it works as a bulk laxative. Other claims are much weaker.
Long use in a tradition is not proof that something works, and it is not proof that it is safe. Both have to be checked on their own.
How does Flax work?
How is flax thought to work?
Most of what flax does seems to come from its fibre. Soluble fibre soaks up water and makes stool softer and bulkier. That effect is well described in people.
The same fibre may trap some bile acids and some fat in the gut. Human trials do show small falls in LDL ("bad") cholesterol with ground seed. The exact route is still argued.
Lignans are changed by gut bacteria into enterolactone and enterodiol. In cell and animal studies, these act weakly like oestrogen. Whether that shifts disease risk in people is not settled.
Alpha-linolenic acid is a plant omega-3 fat. The body turns only a small part of it into the omega-3 fats found in oily fish.
In trials, daily ground flaxseed lowers blood pressure by a few points. The reason is not clear. It may involve the fat, the lignans, or simply more fibre in the diet.
What forms does Flax come in?
What forms does flax come in?
Ground seed is the form with the most human evidence behind it.
Whole seed often passes straight through you. You still get fibre, but little of the oil or the lignans.
Ground seed, sold as flax meal or milled linseed, is what most trials used. It goes into porridge, bread and yoghurt. It turns rancid fast, so it is sold sealed and often kept cold.
Flax oil, also called linseed oil, holds the fat but almost no fibre or lignans. Only food-grade oil is food. Linseed oil sold for wood or paint is not food and must never be eaten.
Capsules hold either the oil or a concentrated lignan extract. Lignan capsules are a supplement, not a food.
Linseed tea and warm poultices were the older home forms. A poultice was a warm paste of soaked seed laid on the skin.
Where it comes from:
What did tradition claim for it?
Flax has been grown in the Nordic countries since the Iron Age, mainly for linen. The seed was food and home remedy on the side.
In Finnish and Swedish households, boiled seed made a slippery gruel. It was given for a dry cough, a sore throat and a blocked gut.
Warm linseed poultices were laid on boils, on the chest and over sore ears. Healers believed the heat and the slime drew out the trouble.
Nordic herbals and pharmacy lists of the 1700s and 1800s carried linseed as a soothing remedy. It stayed in Finnish and Swedish home use well into the 1900s.
Who should avoid Flax?
- Do not eat raw, unripe or green flaxseed, and never in large amounts, because it can release cyanide.
- Never eat linseed oil sold for paint, wood or artists; it is not food and may contain added driers.
- Do not take flaxseed if you have a narrowing or blockage of the bowel (a stricture, or ileus, where the gut stops moving).
- Do not swallow seed if you have trouble swallowing (dysphagia) or a narrowed gullet (oesophagus).
- Do not take flaxseed without a full glass of water.
- Do not take flaxseed within two hours of any medicine you swallow, including levothyroxine (a thyroid tablet).
- Do not use concentrated lignan supplements if you are pregnant or breastfeeding.
- Do not start lignan or high-dose flax supplements if you have a hormone-sensitive cancer, such as most breast cancers, unless your cancer doctor agrees.
- Avoid high-dose flax oil if you take warfarin or another blood thinner, unless your doctor has checked it.
- Avoid flax completely if you have ever had an allergic reaction to flax or linseed.
- Do not use flax in place of prescribed medicine for blood pressure, cholesterol or diabetes.
When should you see a doctor?
When should you see a doctor?
Get urgent help if you have belly pain with no stool or wind, vomiting, or a hard swollen belly. These can mean a gut blockage.
Call emergency services for hives, swelling of the lips, tongue or face, or trouble breathing. Flax allergy is rare but can be severe.
See your doctor if bloating or loose stools last more than two weeks. Speak to your doctor before starting flax if you take blood thinners, diabetes drugs or thyroid tablets.
Is Flax legal where you live?
Flax is an ordinary food in the EU, the UK and the US, sold as seed, meal and oil.
Capsules are sold as food supplements, not as medicines, so strength and purity vary between brands. German and EU food safety bodies have advised limits on raw ground linseed per portion, because of natural cyanide-releasing compounds.
Evidence grades and traditional-use labels are explained in our methodology. Nothing here is medical advice.
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