Flaxseed (also known as linseed) is just what it sounds like - the seed of the flax plant. The typical use of flaxseed is as a source (from the oil of the seeds) of the essential fatty acids linolenic acid (LN) and linoleic acid (LA). Flaxseed oil is about 57% LN (an omega-3) and about 17% LA (an omega-6). LN can be converted into eicosapentaonic acid (EPA) and decosahexanoic acid (DHA) - fatty acids which are precursors to anti-inflammatory and anti-atherogenic prostaglandins. Another beneficial ingredient found in abundance in flax seed is lignan - a phytochemical with potential for cancer prevention.
Flax seed oil is typically used as a dietary supplement for reducing symptoms of PMS and menopause (for which the evidence is thin) and for reducing inflammation and treating various inflammatory conditions such as pain, heart disease, eczema, and psoriasis (where the evidence is modest, but the theory strong based on findings with other fatty acids such as those from fish oil).
Some of the health benefits associated with flaxseed consumption may be due to the presence of compounds known as lignans, which are known to possess various pro- and anti-estrogenic properties. Studies have shown that large doses (several grams) of flaxseed oil each day can reduce blood clotting by reducing platelet aggregation (Allman et al. 1995). Regular flaxseed consumption has also been associated with improvements in the ratio of omega-3 to omega-6 fatty acids in the blood - a situation which may offer protection from atherogenesis and relief from inflammatory conditions (Layne et al. 1996). A number of animal studies have shown a beneficial role of flaxseed oil in delaying breast cancer progression and protecting against colon cancer - sometimes as much as a 50% reduction compared to control groups not fed flaxseed. A clear and consistent reduction in pro-inflammatory markers (tumor necrosis factor and interleukin) has been noted in human subjects supplemented with flaxseed oil (Mest et al. 1983) – but long-term studies showing reductions in disease risk are lacking (McManus et al. 1996).
Effective doses of flaxseed or flaxseed oil of 30-60 grams per day (2-4 tablespoons or 1-2 ounces) are unlikely to pose any adverse side effects. A note of caution is warranted, however, in cases of compromised blood clotting due to the tendency of flaxseed oil to reduce platelet aggregation and prolong bleeding times. A similar cautionary note is advisable for individuals undergoing surgical procedures - which may predispose the patient to excessive bleeding.
1.Allman MA, Pena MM, Pang D. Supplementation with flaxseed oil versus sunflowerseed oil in healthy young men consuming a low fat diet: effects on platelet composition and function. Eur J Clin Nutr. 1995 Mar;49(3):169-78.
2.Beitz J, Mest HJ, Forster W. Influence of linseed oil diet on the pattern of serum phospholipids in man. Acta Biol Med Ger. 1981;40(7-8):K31-K35.
3.Francois CA, Connor SL, Bolewicz LC, Connor WE. Supplementing lactating women with flaxseed oil does not increase docosahexaenoic acid in their milk. Am J Clin Nutr. 2003 Jan;77(1):226-33.
4.Layne KS, Goh YK, Jumpsen JA, Ryan EA, Chow P, Clandinin MT. Normal subjects consuming physiological levels of 18:3(n-3) and 20:5(n-3) from flaxseed or fish oils have characteristic differences in plasma lipid and lipoprotein fatty acid levels. J Nutr. 1996 Sep;126(9):2130-40.
5.Mantzioris E, James MJ, Gibson RA, Cleland LG. Dietary substitution with an alpha-linolenic acid-rich vegetable oil increases eicosapentaenoic acid concentrations in tissues. Am J Clin Nutr. 1994 Jun;59(6):1304-9.
6.Mantzioris E, James MJ, Gibson RA, Cleland LG. Differences exist in the relationships between dietary linoleic and alpha-linolenic acids and their respective long-chain metabolites. Am J Clin Nutr. 1995 Feb;61(2):320-4.
7.McManus RM, Jumpson J, Finegood DT, Clandinin MT, Ryan EA. A comparison of the effects of n-3 fatty acids from linseed oil and fish oil in well-controlled type II diabetes. Diabetes Care. 1996 May;19(5):463-7.
8.Mest HJ, Beitz J, Heinroth I, Block HU, Forster W. The influence of linseed oil diet on fatty acid pattern in phospholipids and thromboxane formation in platelets in man. Klin Wochenschr. 1983 Feb 15;61(4):187-91.
9.Morton MS, Wilcox G, Wahlqvist ML, Griffiths K. Determination of lignans and isoflavonoids in human female plasma following dietary supplementation. J Endocrinol. 1994 Aug;142(2):251-9.
10.Pang D, Allman-Farinelli MA, Wong T, Barnes R, Kingham KM. Replacement of linoleic acid with alpha-linolenic acid does not alter blood lipids in normolipidaemic men. Br J Nutr. 1998 Aug;80(2):163-7.
11.St-Onge MP, Lamarche B, Mauger JF, Jones PJ. Consumption of a functional oil rich in phytosterols and medium-chain triglyceride oil improves plasma lipid profiles in men. J Nutr. 2003 Jun;133(6):1815-20.
12.Tarpila S, Aro A, Salminen I, Tarpila A, Kleemola P, Akkila J, Adlercreutz H. The effect of flaxseed supplementation in processed foods on serum fatty acids and enterolactone. Eur J Clin Nutr. 2002 Feb;56(2):157-65.
13.Wallace FA, Miles EA, Calder PC. Comparison of the effects of linseed oil and different doses of fish oil on mononuclear cell function in healthy human subjects. Br J Nutr. 2003 May;89(5):679-89.
EDITOR'S NOTE: This monograph can be found in The Health Professional's Guide to Dietary Supplements (Lippincott, Williams & Wilkins) by Shawn M. Talbott, PhD and Kerry Hughes, MS