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Herbs & Supplements:
Flaxseed
Alternate Names
Linseed
Principal Proposed Uses
Constipation, Irritable Bowel Syndrome
Other Proposed Uses
Diverticulitis, Atherosclerosis Prevention, Elevated Cholesterol, Cancer Prevention, Menopausal Symptoms, Kidney Disease, Gastritis, Gastroenteritis, Painful Skin Inflammation (topical)
Flaxseeds are the hard, tiny seeds of Linum usitatissimum, the flax plant that has been widely used for thousands of years as a source of food and clothing. So far, scientists have isolated at least three flaxseed components with potential health benefits. The first is fiber, valuable in treating constipation. The benefits of the other two substances, alpha-linolenic acid (a type of omega-3 fatty acid) and lignans, are not yet fully confirmed; still, preliminary research suggests that these components may be helpful in prevention of cancer and heart disease and perhaps in treatment of chronic kidney disease and menopausal symptoms.
The oil made from flaxseed has no appreciable amounts of lignans but it does contain alpha-linolenic acid. See flaxseed oil and lignans for more information on these substances.
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What Is Flaxseed Used for Today?
Germany's Commission E authorizes the use of flaxseed for various digestive problems, such as chronic constipation, irritable bowel syndrome, diverticulitis, and general stomach discomfort.1 The fiber in flaxseed binds with water, swelling to form a soothing gel which helps soften the stool and move it along in the intestines. The natural action of fiber-containing foods such as flaxseed can be particularly helpful when constipation is chronic. At least one study has found that flaxseed can help with chronic constipation in irritable bowel disease.2
Like other high-fiber foods, flaxseed may also be helpful in reducing cholesterol.3,4,5 It's possible that besides the effects of its fiber, other components of flax, such as its lignans or oil, may help lower cholesterol and prevent atherosclerosis.610
Flaxseed, its lignans, and its oil are also being investigated for potential cancer prevention or even treatment.1118 In addition, very preliminary research indicates potential benefits in treating menopausal symptoms and certain kidney diseases.19,20,21
Warning: Do not use flaxseed to treat kidney disease or cancer without a doctor's supervision, because these conditions are potentially quite serious.
Because of its soothing nature, flaxseed is routinely used in Europe for symptomatic relief of short-term inflammation of the stomach and intestines (gastritis or gastroenteritis) as well as applied externally for painful skin inflammations.22 However, research on these uses is fairly minimal.
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What Is the Scientific Evidence for Flaxseed?
Constipation
In a double-blind study, 55 people with chronic constipation caused by irritable bowel syndrome received either ground flaxseed or psyllium seed (a well-known treatment for constipation) daily for 3 months.23 Those taking flaxseed had significantly fewer problems with constipation, abdominal pain, and bloating than those taking psyllium. The flaxseed group had even further improvements in constipation and bloating while continuing their treatment in the 3 months after the double-blind study ended. The researcher concluded that flaxseed relieved constipation more effectively than psyllium.
Cholesterol and Atherosclerosis
Several human studies have found that flaxseed lowers cholesterol.24,25,26,58 In one double-blind study, 38 older women with high cholesterol ate bread or muffins containing either flaxseed or sunflower seed for 6 weeks, later switching to the opposing treatment for another 6 weeks.27 Total cholesterol dropped with both regimens, but only those on the flaxseed regimen had significantly lower LDL, the "bad" cholesterol. In another investigation, 29 men and older women with high cholesterol ate muffins with either partially defatted flaxseed or a wheat bran placebo for 3 weeks each.28 Those eating flaxseed showed significant decreases in both total and LDL cholesterol, compared to little change with placebo.
Finally, in the double-blind study on constipation mentioned earlier, both treatmentsflaxseed and psylliumled to a 10% reduction in total cholesterol and a 14% reduction in LDL cholesterol.29 In none of these studies did flaxseed lower HDL ("good") cholesterol.
Flaxseed may also have a direct effect in preventing atherosclerosis, a condition in which arteries become lined with fatty deposits. Two rabbit studies found that both flaxseed and one of its lignans prevented atherosclerosis.30,31 The lignan also lowered the rabbits' cholesterol, but flaxseed by itself did not.
The oil from flaxseeds has been suggested as an alternative to fish oil in prevention of heart disease. Fish oil, however, lowers blood triglyceride levels as its main effect, and flaxseed oil does not affect triglyceride levels.32
Cancer
Scientists are investigating whether flaxseed or its lignans can help prevent or treat cancer, particularly cancer of the breast and colon. Observational studies suggest that people who eat more lignan-containing foods have a lower incidence of breast and perhaps colon cancer.33 However, other factors may have been responsible for these outcomes.
The lignans in flaxseed are phytoestrogens, plant chemicals mimicking the effects of estrogen in the body: phytoestrogens hook onto the same spots on cells where estrogen attaches. If there is little estrogen in the body, for example after menopause, lignans may act like weak estrogen. However, when natural estrogen is abundant, lignans may reduce the hormone's effects by displacing it from cells; displacing estrogen in this manner may help prevent those cancers that depend on estrogen, such as breast cancer, from starting and developing. (This is also how soy is believed to work in breast cancer prevention, although the phytoestrogens in soy are isoflavones.)
Some preliminary research indicates that these lignans may also fight cancer in other ways, perhaps by acting as antioxidants.34,35,36
Animal investigations using flaxseed and its lignans offer supporting evidence for a potential cancer-preventive or even cancer-treatment effect; several found that one or the other inhibited breast and colon cancer in animals37,38,39 and reduced metastases from melanoma (a type of skin cancer) in mice.40 Test tube studies found that flaxseed or one of its lignans inhibited the growth of human breast cancer cells,41 and that the lignans enterolactone and enterodiol inhibited the growth of human colon tumor cells.42 This preliminary research is promising, but much more is needed before we can draw any conclusions.
Although much of this anticancer work has focused on the lignans in flaxseed, one study also found that flaxseed oilwhich contains no appreciable amounts of lignansslowed the growth of malignant breast tumors in rats.43
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Therapeutic Dosages
According to the European Scientific Cooperative on Phytotherapy, the usual dose of flaxseed for constipation is 5 g of whole, cracked, or freshly crushed seeds soaked in water and taken with a glassful of liquid 3 times a day.44 Expect effects to begin 18 to 24 hours later. Because of this time delay, it's recommended to take flaxseed for a minimum of 2 to 3 days. Children aged 6 to 12 should be given half the adult dose, while children younger than 6 should be treated only under the guidance of a physician.45
In one study, people received 6 to 24 g per day of flaxseed for 6 months for constipation caused by irritable bowel syndrome.46
To soothe an upset stomach, soak 5 to 10 g of whole flaxseed in a half cup of water, strain after 20 to 30 minutes, then drink.47 For painful skin inflammations, the recommended dose is 30 to 50 g of crushed or powdered seed applied externally as a warm poultice or compress.48
Like other sources of fiber, flaxseed should be taken with plenty of fluids, or it may actually worsen constipation. Also, it's best to start with smaller doses and then increase.
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Safety Issues
Flaxseed is generally believed to besafe. However, there are some potential risks to consider.
As with many substances, there have been reports of life-threatening allergic reactions to flaxseed.
Because of its potential effects on estrogen, pregnant or breast-feeding women should probably avoid flaxseed. One study found that pregnant rats who ate large amounts of flaxseed (5% or 10% of their diet), or one of its lignans, gave birth to offspring with altered reproductive organs and functions49in humans, eating 25 g of flaxseed per day amounts to about 5% of the diet.50 Lignans were also found to be transferred to baby rats during nursing.51 Additionally, a study of postmenopausal women found that use of flaxseed reduced estrogen levels and increased levels of prolactin.59 This suggests hormonal effects that could be problematic in pregnancy.
Flaxseed may not be safe for women with a history of estrogen-sensitive cancer, such as breast cancer or uterine cancer. A few test tube studies suggest that certain cancer cells can be stimulated by lignans such as those present in flaxseed.52 Other studies found that lignans inhibit cancer cell growth.53 As with estrogen, lignans' positive or negative effects on cancer cells may depend on dose, type of cancer cell, and levels of hormones in the body. If you have a history of cancer, particularly breast cancer, talk with your doctor before consuming large amounts of flaxseeds.
If you have diabetes, flaxseed (like other high-fiber foods) may delay glucose absorption.54 This may lead to better blood sugar control but it also may increase the risk of hypoglycemic reactions. Talk with your doctor about appropriate use.
Finally, flaxseeds contain tiny amounts of cyanide-containing substances, which can be a problem among livestock eating large amounts of flax.55 While normal cooking and baking of whole flaxseeds or flour eliminates any detectable amounts of cyanide,56 it is at least theoretically possible that eating huge amounts of raw or unprocessed flaxseeds or flaxseed meal could pose a problem. However, most authorities do not think this presents much of a risk in real life.57
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References
1. Blumenthal M, ed. The Complete German Commission E Monographs, Therapeutic Guide to Herbal Medicine. Boston, Mass: Integrative Medicine Communications; 1998, 132 [footnote].
2. Tarpila S, Kivinen A. Ground flaxseed is an effective hypolipidemic bulk laxative [abstract]. Gastroenterology. 1997;112:A836.
3. Arjmandi BH, Khan DA, Juma S, et al. Whole flaxseed consumption lowers serum LDL-cholesterol and lipoprotein(a) concentrations in postmenopausal women. Nutr Res. 1998;18:12031214.
4. Jenkins DJ, Kendall CW, Vidgen E, et al. Health aspects of partially defatted flaxseed, including effects on serum lipids, oxidative measures, and ex vivo androgen and progestin activity: a controlled crossover trial. Am J Clin Nutr. 1999;69:395402.
5. Tarpila S, Kivinen A. Ground flaxseed is an effective hypolipidemic bulk laxative [abstract]. Gastroenterology. 1997;112:A836.
6. Arjmandi BH, Khan DA, Juma S, et al. Whole flaxseed consumption lowers serum LDL-cholesterol and lipoprotein(a) concentrations in postmenopausal women. Nutr Res. 1998;18:12031214.
7. Jenkins DJ, Kendall CW, Vidgen E, et al. Health aspects of partially defatted flaxseed, including effects on serum lipids, oxidative measures, and ex vivo androgen and progestin activity: a controlled crossover trial. Am J Clin Nutr. 1999;69:395402.
8. Tarpila S, Kivinen A. Ground flaxseed is an effective hypolipidemic bulk laxative [abstract]. Gastroenterology. 1997;112:A836.
9. Prasad K. Dietary flax seed in prevention of hypercholesterolemic atherosclerosis. Atherosclerosis. 1997;132:6976.
10. Prasad K. Reduction of serum cholesterol and hypercholesterolemic atherosclerosis in rabbits by secoisolariciresinol diglucoside isolated from flaxseed. Circulation. 1999;99:13551362.
11. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. 1997;29:95120.
12. Thompson LU. Experimental studies on lignans and cancer. Baillieres Clin Endocrinol Metab.1998;12:691705.
13. Thompson LU, Rickard SE, Orcheson LJ, et al. Flaxseed and its lignan and oil components reduce mammary tumor growth at a late stage of carcinogenesis. Carcinogenesis. 1996;17:13731376.
14. Serraino M, Thompson LU. The effect of flaxseed supplementation on the initiation and promotional stages of mammary tumorigenesis. Nutr Cancer. 1992;17:153159.
15. Yan L, Yee JA, Li D, et al. Dietary flaxseed supplementation and experimental metastasis of melanoma cells in mice. Cancer Lett. 1998;124:181186.
16. Sung MK, Lautens M, Thompson LU. Mammalian lignans inhibit the growth of estrogen-independent human colon tumor cells. Anticancer Res. 1998;18:14051408.
17. Bougnoux P, Koscielny S, Chajes V, et al. Alpha-linolenic acid content of adipose breast tissue: a host determinant of the risk of early metastasis in breast cancer. Br J Cancer. 1994;70:330334.
18. Rose DP. Dietary fatty acids and cancer. Am J Clin Nutr. 1997;66(suppl):S998S1003.
19. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. 1997;29:95120.
20. Clark WF, Parbtani A, Huff MW, et al. Flaxseed: a potential treatment for lupus nephritis. Kidney Int. 1995;48:475480.
21. Ogborn MR, Nitschmann E, Bankovic-Calic N, et al. The effect of dietary flaxseed supplementation on organic anion and osmolyte content and excretion in rat polycystic kidney disease. Biochem Cell Biol. 1998;76:553559.
22. Fascicule 1. Lini semen, linseed. In: European Scientific Cooperative on Phytotherapy. Monographs on the medicinal uses of plant drugs. Dusseldorf, Germany : IDW-Verlag. 1997:15.
23. Tarpila S, Kivinen A. Ground flaxseed is an effective hypolipidemic bulk laxative [abstract]. Gastroenterology. 1997;112:A836.
24. Arjmandi BH, Khan DA, Juma S, et al. Whole flaxseed consumption lowers serum LDL-cholesterol and lipoprotein(a) concentrations in postmenopausal women. Nutr Res. 1998;18:12031214.
25. Jenkins DJ, Kendall CW, Vidgen E, et al. Health aspects of partially defatted flaxseed, including effects on serum lipids, oxidative measures, and ex vivo androgen and progestin activity: a controlled crossover trial. Am J Clin Nutr. 1999;69:395402.
26. Tarpila S, Kivinen A. Ground flaxseed is an effective hypolipidemic bulk laxative [abstract]. Gastroenterology. 1997;112:A836.
27. Arjmandi BH, Khan DA, Juma S, et al. Whole flaxseed consumption lowers serum LDL-cholesterol and lipoprotein(a) concentrations in postmenopausal women. Nutr Res. 1998;18:12031214.
28. Jenkins DJ, Kendall CW, Vidgen E, et al. Health aspects of partially defatted flaxseed, including effects on serum lipids, oxidative measures, and ex vivo androgen and progestin activity: a controlled crossover trial. Am J Clin Nutr. 1999;69:395402.
29. Tarpila S, Kivinen A. Ground flaxseed is an effective hypolipidemic bulk laxative [abstract]. Gastroenterology. 1997;112:A836.
30. Prasad K. Dietary flax seed in prevention of hypercholesterolemic atherosclerosis. Atherosclerosis. 1997;132:6976.
31. Prasad K. Reduction of serum cholesterol and hypercholesterolemic atherosclerosis in rabbits by secoisolariciresinol diglucoside isolated from flaxseed. Circulation. 1999;99:13551362.
32. Harris WS. N-3 fatty acids and serum lipoproteins: human studies. Am J Clin Nutr. 1997;65(5 suppl):S1645S1654.
33. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. 1997;29:95120.
34. Sung MK, Lautens M, Thompson LU. Mammalian lignans inhibit the growth of estrogen-independent human colon tumor cells. Anticancer Res. 1998;18:14051408.
35. Prasad K. Hydroxyl radical-scavenging property of secoisolariciresinol diglucoside (SDG) isolated from flax-seed. Mol Cell Biochem. 1997;168:117123.
36. Yuan YV, et al. Short-term feeding of flaxseed or its lignan has minor influence on in vivo hepatic antioxidant status in young rats. Nutr Res. 1999;19:12331243.
37. Thompson LU. Experimental studies on lignans and cancer. Baillieres Clin Endocrinol Metab.1998;12:691705.
38. Thompson LU, Rickard SE, Orcheson LJ, et al. Flaxseed and its lignan and oil components reduce mammary tumor growth at a late stage of carcinogenesis. Carcinogenesis. 1996;17:13731376.
39. Serraino M, Thompson LU. The effect of flaxseed supplementation on the initiation and promotional stages of mammary tumorigenesis. Nutr Cancer. 1992;17:153159.
40. Yan L, Yee JA, Li D, et al. Dietary flaxseed supplementation and experimental metastasis of melanoma cells in mice. Cancer Lett. 1998;124:181186.
41. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. 1997;29:95120.
42. Sung MK, Lautens M, Thompson LU. Mammalian lignans inhibit the growth of estrogen-independent human colon tumor cells. Anticancer Res. 1998;18:14051408.
43. Thompson LU, Rickard SE, Orcheson LJ, et al. Flaxseed and its lignan and oil components reduce mammary tumor growth at a late stage of carcinogenesis. Carcinogenesis. 1996;17:13731376.
44. Fascicule 1. Lini semen, linseed. In: European Scientific Cooperative on Phytotherapy. Monographs on the medicinal uses of plant drugs. Dusseldorf, Germany : IDW-Verlag. 1997:15.
45. Fascicule 1. Lini semen, linseed. In: European Scientific Cooperative on Phytotherapy. Monographs on the medicinal uses of plant drugs. Dusseldorf, Germany : IDW-Verlag. 1997:15.
46. Tarpila S, Kivinen A. Ground flaxseed is an effective hypolipidemic bulk laxative [abstract]. Gastroenterology. 1997;112:A836.
47. Fascicule 1. Lini semen, linseed. In: European Scientific Cooperative on Phytotherapy. Monographs on the medicinal uses of plant drugs. Dusseldorf, Germany : IDW-Verlag. 1997:15.
48. Fascicule 1. Lini semen, linseed. In: European Scientific Cooperative on Phytotherapy. Monographs on the medicinal uses of plant drugs. Dusseldorf, Germany : IDW-Verlag. 1997:15.
49. Tou JCL, Chen J, Thompson LU. Flaxseed and its lignan precursor, secoisolariciresinol diglycoside, affect pregnancy outcome and reproductive development in rats. J Nutr. 1998;128:18611868.
50. Thompson LU. Experimental studies on lignans and cancer. Baillieres Clin Endocrinol Metab.1998;12:691705.
51. Tou JCL, Chen J, Thompson LU. Flaxseed and its lignan precursor, secoisolariciresinol diglycoside, affect pregnancy outcome and reproductive development in rats. J Nutr. 1998;128:18611868.
52. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. 1997;29:95120.
53. Adlercreutz H, Mazur W. Phyto-oestrogens and Western diseases. Ann Med. 1997;29:95120.
54. Fascicule 1. Lini semen, linseed. In: European Scientific Cooperative on Phytotherapy. Monographs on the medicinal uses of plant drugs. Dusseldorf, Germany : IDW-Verlag. 1997:15.
55. Wanasundara PKJPD, Shahidi F. Process-induced compositional changes of flaxseed. Adv Exp Med Biol. 1998;434:307325.
56. Wanasundara PKJPD, Shahidi F. Process-induced compositional changes of flaxseed. Adv Exp Med Biol. 1998;434:307325.
57. Fascicule 1. Lini semen, linseed. In: European Scientific Cooperative on Phytotherapy. Monographs on the medicinal uses of plant drugs. Dusseldorf, Germany: IDW-Verlag. 1997:15.
58. Lucas EA, Wild RD, Hammond LJ, et al. Flaxseed improves lipid profile without altering biomarkers of bone metabolism in postmenopausal women. J Clin Endocrinol Metab. 2002;87:1527-1532.
59. Hutchins AM, Martini MC, Olson BA, et al. Flaxseed consumption influences endogenous hormone concentrations in postmenopausal women. Nutr Cancer. 2001;39:58-65.
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May 2002
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