Flaxseed Oil

Also indexed as: Lignan, Linseed Oil, Linum usitatissimum

What does it do? Like most vegetable oils, flaxseed oil contains linoleic acid, an essential fatty acid needed for survival. But unlike most oils, it also contains significant amounts of another essential fatty acid, alpha linolenic acid (ALA).

ALA is an omega-3 fatty acid. To a limited extent, the body turns ALA into eicosapentaenoic acid (EPA)—an omega-3 fatty acid found in fish oil—which in turn converts to beneficial prostaglandins. (Prostaglandins are hormone-like substances made in many parts of the body rather than coming from one organ, as most hormones do.) While fish oil has been shown to have anti-inflammatory activity, an anti-inflammatory effect of flaxseed oil has not been demonstrated conclusively.

Some doctors have argued that, because ALA can be converted to EPA and DHA (the fatty acids found in fish oil), flaxseed oil should be useful for the same conditions as fish oil. However, the conversion of ALA to EPA and DHA is limited, so that argument may turn out to be incorrect. For example, while numerous studies have shown that fish oils are beneficial for rheumatoid arthritis, flaxseed oil failed to work for this condition in the only known trial.1 In 1994, a diet purportedly high in ALA was successful in preventing heart disease,2 but this study altered many dietary factors, so ALA may not have been solely responsible for the outcome.3 Flaxseed oil does not appear to be a good replacement for fish oil for people with elevated triglycerides.4 5 ALA does not reduce excess platelet aggregation (“sticky platelets”), another risk factor for heart disease, the way fish oil does.6 However, flaxseed oil may help lower cholesterol,7 and research specific to flaxseed oil indicates that it may also lower blood pressure.8

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.

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

Rating Health Concerns
3Stars Constipation (flaxseed)
2Stars High cholesterol (flaxseed)
1Star Benign prostatic hyperplasia (BPH)
Constipation
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 An herb is primarily supported by traditional use, or the herb or supplement has 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.

How much is usually taken? 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,9 and this conversion can be increased by restricting the intake of other vegetable oils.10

For those who wish to replace fish oil with flaxseed oil, research suggests taking up to ten times as much ALA as EPA.11 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,12 13 14 15 16 one animal study17 and a preliminary human study18 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.19 For prostate cancer, a test tube study reported ALA promoted cancer cell growth,20 but preliminary human studies have shown ALA to be associated with either an increased21 22 or decreased risk,23 or no change24 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,25 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.

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

References:

1. Nordstrom DC, Honkanen VE, Nasu Y, et al. Alpha-linolenic acid in the treatment of rheumatoid arthritis. A double-blind, placebo-controlled and randomized study: flaxseed vs. safflower seed. Rheumatol Int 1995;14:231–4.

2. De Lorgeril M, Renaud S, Maelle N, et al. Mediterranean alpha-linolenic acid-rich diet in secondary prevention of coronary heart disease. Lancet 1994;343:1454–9.

3. Rice RD. Mediterranean diet. Lancet 1994;344;893–4 [letter].

4. Kelley DS, Nelson GJ, Love JE, et al. Dietary a-linolenic acid alters tissue fatty acid composition, but not blood lipids, lipoproteins or coagulation status in humans. Lipids 1993;28:533–7.

5. Abbey M, Clifton P, Kestin M, et al. Effect of fish oil on lipoproteins, lecithin: cholesterol acyltransferase, and lipid transfer protein activity in humans. Arterioscler 1990;10:85–94.

6. Wensing AGCL, Mensink RP, Hornstra G. Effects of dietary n-3 polyunsaturated fatty acids from plant and marine origin on platelet aggregation in healthy elderly subjects. Br J Nutr 1999;82:183–91.

7. Chan JK, Bruce VM, McDonald BE. Dietary a-linolenic acid is as effective as oleic acid and linoleic acid in lowering blood cholesterol in normolipidemic men. Am J Clin Nutr 1991;53:1230–4.

8. Singer P, Jaeger W, Berger I, et al. Effects of dietary oleic, linoleic and a-linolenic acids on blood pressure, serum lipids, lipoproteins and the formation of eicosanoid precursors in patients with mild essential hypertension. J Human Hypertension 1990;4:227–33.

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.

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

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

18. 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.

19. 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.

20. 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.

21. 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.

22. 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.

23. 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.

24. 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.

25. 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.