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Flaxseed and Flaxseed Oil

Also indexed as: Lignan, Linseed Oil, Linum usitatissimum


Flaxseed, called linseed in some countries, is a good source of dietary fiber, omega-3 fatty acids, and lignans. Each of these components may contribute to the health effects of eating flaxseed, but flaxseed oil contains no fiber and very little lignan.

Where is it found?

In addition to its presence in flaxseed oil, small amounts of ALA are also found in canola, soy, black currant, and walnut oils. Small amounts of lignans are present in a wide variety of foods of plant origin.

Flaxseed and flaxseed oil has been used in connection with the following conditions (refer to the individual health concern for complete information):

Science Ratings Health Concerns

Constipation (flaxseed)

Systemic lupus erythematosus (flaxseed)


High cholesterol (flaxseed)



Benign prostatic hyperplasia (BPH) (flaxseed oil)

Constipation (flaxseed oil)

Ulcerative colitis (flaxseed)

3Stars Reliable and relatively consistent scientific data showing a substantial health benefit.
2Stars Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
1Star For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit.

Who is likely to be deficient?

ALA deficiencies are possible but believed to be rare, except in infants who are fed formula that is omega-3 deficient. Lignan is not an essential nutrient, so deficiencies are not possible.

How much is usually taken?

For promoting bowel regularlity, 1 tablespoon (15 ml) of whole or ground flaxseed is taken one or two times per day, accompanied by a full glass of water. When used to treat other health conditions, it is used in amounts of 30 to 35 grams (1 to 2 ounces) per day.

Although it is not suitable for cooking, flaxseed oil (unlike fish oil) can be used in salads. Some doctors recommend that people use 1 tablespoon (15 ml) of flaxseed oil per day as a supplement in salads or on vegetables to ensure a supply of essential fatty acids. Some conversion of ALA to EPA does occur,1 and this conversion can be increased by restricting the intake of other vegetable oils.2

For those who wish to replace fish oil with flaxseed oil, research suggests taking up to ten times as much ALA as EPA.3 Typically, this means 7.2 grams of flaxseed oil equals 1 gram of fish oil. However, even if taken in such high amounts, flaxseed oil may not have the same effects as fish oil. But, flaxseed oil will not cause a fishy-smelling burp (a possible side effect of fish oil).

Are there any side effects or interactions?

Flaxseed oil toxicity has not been reported. However, there is conflicting information about the effect of flaxseed oil and one of its major constituents, ALA, on cancer risk.

While most test tube and animal studies suggest a possible protective role for ALA against breast cancer,4 5 6 7 8 one animal study9 and a preliminary human study10 suggested increased breast cancer risk from high dietary ALA. Another preliminary human study reported that higher breast tissue levels of ALA are associated with less advanced breast cancer at the time of diagnosis.11 For prostate cancer, a test tube study reported ALA promoted cancer cell growth,12 but preliminary human studies have shown ALA to be associated with either an increased13 14 or decreased risk,15 or no change16 at all.

Advocates of flaxseed oil speculate that a potential association between ALA and cancer may be due to the fact that meat contains ALA, thus implicating ALA when the real culprits are probably other components of meat. In some studies, however, saturated fat (and therefore probably meat) were taken into consideration, and ALA still correlated with increased risk. The associations between ALA and cancer might eventually be shown to be caused by substances found in foods rich in ALA rather than by ALA itself. However, ALA has been reported to become mutagenic (able to cause precancerous changes) when heated,17 which concerns some doctors.

The effect of ALA as an isolated substance, and of flaxseed oil on the risk of cancer in humans remains unclear, with most animal and test tube studies suggesting protection, and some preliminary human trials suggesting cause for concern. It is premature to suggest that ALA and flaxseed oil will either cause or protect against human cancer at this time.

Flaxseed oil is not suitable for cooking and should be stored in an opaque, airtight container in the refrigerator or freezer. If the oil has a noticeable odor it is probably rancid and should be discarded.

As with any source of fiber, flaxseed should not be taken if there is possibility that the intestines are obstructed. People with scleroderma (systemic sclerosis) should consult a doctor before using flaxseed. Although a gradual introduction of fiber in the diet may improve bowel symptoms in some cases, there have been several reports of people with scleroderma developing severe constipation and even bowel obstruction requiring hospitalization after fiber supplementation.18

Animal research suggests that large amounts of flaxseed or lignans consumed during pregnancy might adversely affect the development of the reproductive system.19 No studies have attempted to investigate whether this could be a problem in humans.

Allergic reactions to flaxseed have occasionally been reported, but are considered very uncommon.20 21

At the time of writing, there were no well-known drug interactions with flaxseed oil.


1. Sanders TAB, Roshanai F. The influence of different types of omega 3 polyunsaturated fatty acids on blood lipids and platelet function in healthy volunteers. Clin Sci 1983;64:91.

2. Mantzioris E, James MJ, Gibson RA, Cleland LG. Dietary substitution with alpha-linolenic acid-rich vegetable oil increases eicosapentaenoic acid concentrations in tissues. Am J Clin Nutr 1994;59:1304–49.

3. Indu M, Ghafoorunissa. n-3 fatty acids in Indian diets: comparison of the effects of precursor (alpha-linolenic acid) vs product (long-chain n-3 polyunsaturated fatty acids). Nutr Res 1992;12:569–82.

4. Chajes V, Sattler W, Stranzl A, Kostner GM. Influence of n-3 fatty acids on the growth of human breast cancer cells in vitro: relationship to peroxides and vitamin E. Breast Cancer Res Treat 1995;34:199–212.

5. Munõz SF, Silva RA, Lamarque A, et al. Protective capability of dietary Zizyphus mistol seed oil, rich in 18:3, n-3, on the development of two murine mammary gland adenocarcinomas with high or low metastatic potential. Prostaglandins Leukot Essent Fatty Acids 1995;53:135–8.

6. Thompson LU, Rickard SE, Orcheson LJ, Seidl MM. Flaxseed and its lignan and oil components reduce mammary tumor growth at a late stage of carcinogenesis. Carcinogenesis 1996;17:1373–6.

7. Fritsche KL, Johnston PV. Effect of dietary alpha-linolenic acid on growth, metastasis, fatty acid profile and prostaglandin production of two murine mammary adenocarcinomas. J Nutr 1990;120:1601–9.

8. Cave WT Jr. Dietary n-3 (omega-3) polyunsaturated fatty acid effects on animal tumorigenesis. FASEB J 1991;5:2160–6 [review].

9. Braden LM, Carroll KK. Dietary polyunsaturated fat in relation to mammary carcinogenesis in rats. Lipids 1986;21:285–8.

10. De Stefani E, Deneo-Pellegrini H, Mendilaharsu M, Ronco A. Essential fatty acids and breast cancer; a case-control study in Uruguay. Int J Cancer 1998;76:491–4.

11. Bougnoix P. Alpha-linolenic acid content of adipose breast tissue: a host determinant of the risk of early metastasis in breast cancer. Br J Cancer 1994;70:330–40.

12. Pandalai PK, Pilat MJ, Yamazaki K, et al. The effects of omega-3 and omega-6 fatty acids on in vitro prostate cancer growth. Anticancer Res 1996;16:815–20.

13. Giovannucci E, Rimm EB, Colditz GA, et al. A prospective study of dietary fat and risk of prostate cancer. J Natl Cancer Inst 1993;85:1571–9.

14. Harvei S, Bjerve KS, Tretli S, et al. Prediagnostic level of fatty acids in serum phospholipids: omega-3 and omega-6 fatty acids and the risk of prostate cancer. Int J Cancer 1997;71:545–51.

15. Gann PH, Hennekens CH, Sacks FM, et al. Prospective study of plasma fatty acids and risk of prostate cancer. J Natl Cancer Inst 1994;86:281–6.

16. Schuurman AG, van den Brandt PA, Dorant E, et al. Association of energy and fat intake with prostate carcinoma risk: results from the Netherlands Cohort Study. Cancer 1999;86:1019–27.

17. Shields PG, Xu GX, Blot WJ, et al. Mutagens from heated Chinese and U.S. cooking oils. J Natl Cancer Inst 1995;87:836–41.

18. Gough A, Sheeran T, Bacon P, Emery P. Dietary advice in systemic sclerosis: the dangers of a high fibre diet. Ann Rheum Dis 1998;57:641–2.

19. Tou JC, Chen J, Thompson LU. Flaxseed and its lignan precursor, secoisolariciresinol diglycoside, affect pregnancy outcome and reproductive development in rats. J Nutr 1998;128:1861–8.

20. Alonso L, Marcos ML, Blanco JG, et al. Anaphylaxis caused by linseed (flaxseed) intake. J Allergy Clin Immunol 1996;98:469–70.

21. Leon F, Rodriguez M, Cuevas M. Anaphylaxis to Linum. Allergol Immunopathol (Madr) 2003;31:47–9.

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