Also known as: Linseed, Alpha-linolenic acid, ALA, Linum usitatissimum, Lignans
FoundationalGood evidence
The richest plant source of the omega-3 fat ALA, plus useful fibre and lignans. The catch is that humans convert ALA to EPA and DHA very poorly, so it does not replace marine omega-3.
Typical dose
10.0–30.0 g per day
Any time, with water; grind fresh where possible
What it is
Flaxseed, also called linseed, is the seed of Linum usitatissimum. It supplies three things worth having: alpha-linolenic acid, soluble and insoluble fibre, and lignans.
ALA is an omega-3 fatty acid, which is where the confusion starts. It sits at the top of the omega-3 family, and EPA and DHA are made from it, but the conversion in humans is inefficient.
Roughly 5 to 10 per cent of ALA converts to EPA, and considerably less than 1 per cent reaches DHA. A label describing flaxseed as an omega-3 source is technically accurate and practically misleading for anyone relying on it instead of marine omega-3.
How it works
ALA is converted through a series of enzyme steps to EPA and then DHA. The same enzymes also process omega-6 fats, and because most diets supply far more omega-6, the pathway is effectively competed for.
ALA has some effects of its own beyond being a precursor, and it is an essential fatty acid in its own right.
Flaxseed lignans are converted by gut bacteria into compounds with weak oestrogen-like activity, which is a separate strand of research from the fatty acid content. The soluble fibre also forms a gel, contributing to the effects on lipids and bowel regularity.
What the evidence shows
Whole flaxseed has reasonable evidence for modest reductions in blood pressure and lipid markers, likely driven by the combination of fibre, lignans and ALA rather than any one component.
Bowel regularity findings are consistent, as would be expected from a high-fibre seed.
On raising EPA and DHA status, the evidence is clear and negative. Trials feeding substantial ALA raise EPA only slightly and DHA barely at all. Anyone eating plant-based who wants EPA and DHA needs algal oil, and flaxseed will not do that job.
Dosing
Typical intake is 10 to 30 g of ground flaxseed daily, roughly one to three tablespoons.
Grind it. Whole flaxseed passes through the digestive tract largely intact, so you get the fibre and very little else. Grinding fresh is best, since the fats oxidise quickly once the seed is broken.
Flaxseed oil supplies ALA without the fibre or lignans, and is highly prone to going rancid. Keep it refrigerated, buy small bottles, and never cook with it. Drink plenty of water alongside ground seed, as with any fibre.
Effects on lipids and regularity accrue over weeks
Timing
Any time, with water; grind fresh where possible
Competition status
Permitted — not on the WADA Prohibited List
Category
Foundational
Safety and side effects
Flaxseed is a food and is well tolerated. Bloating and gas are common when starting, and settle with time and gradual increases.
Adequate fluid matters, as with any fibre, and fibre can reduce absorption of medication taken at the same time.
The lignans have weak oestrogen-like activity, so speak to your doctor before taking large amounts if your hormones are being monitored or managed. Flaxseed oil in particular goes rancid quickly, and rancid oil is worth avoiding rather than tolerating.
Who should avoid it
Separate from medication by at least two hours, since fibre reduces absorption. Speak to your doctor before large intakes if your hormones are being monitored or managed, given the lignan content. Take with adequate fluid and build up gradually. Keep flaxseed oil refrigerated and discard it once it smells off.
This entry is provided for information only. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Consult a qualified healthcare professional before use if you are pregnant, breastfeeding, taking medication or under medical supervision.
