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Flaxseed Contributions by ColleenO

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Safety Issues

Flaxseed is generally believed to be safe. 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 breastfeeding 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 functions 1 —in humans, eating 25 g of flaxseed per day amounts to about 5% of the diet. 2 Lignans were also found to be transferred to baby rats during nursing. 3 Additionally, a study of postmenopausal women found that use of flaxseed reduced estrogen levels and increased levels of prolactin. 4 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 or uterine cancer. A few test tube studies suggest that certain cancer cells can be stimulated by lignans such as those present in flaxseed. 5 Other studies found that lignans inhibit cancer cell growth. 6 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. 7 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. 8 While normal cooking and baking of whole flaxseeds or flour eliminates any detectable amounts of cyanide, 9 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. 10

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  • Naturopathic doctor
  • Clinical nutritionist or registered dietitian
  • Integrative MD
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For information on dosage, sources and specific safety issues, see the following articles:

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  1. Dodin S, Lemay A, Jacques H, Légaré F, Forest JC, Mâsse B. The effects of flaxseed dietary supplement on lipid profile, bone mineral density, and symptoms in menopausal women: a randomized, double-blind, wheat germ placebo-controlled clinical trial. J Clin Endocrinol Metab. 90(3):1390-7.
  2. Prasad K. Dietary flax seed in prevention of hypercholesterolemic atherosclerosis. Atherosclerosis. 1997;132:69-76.
  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;18:1203-1214.
  4. Singer P, Jaeger W, Berger I, et al. Effects of dietary oleic, linoleic, and alpha-linolenic acids on blood pressure, serum lipids, lipoproteins and the formation of eicosanoid precursors in patients with mild essential hypertension. J Hum Hypertens. 1990;4:227-233.
  5. Prasad K. Reduction of serum cholesterol and hypercholesterolemic atherosclerosis in rabbits by secoisolariciresinol diglucoside isolated from flaxseed. Circulation. 1999;99:1355-1362.
  6. 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;69:395-402.
  7. Tarpila S, Kivinen A. Ground flaxseed is an effective hypolipidemic bulk laxative [abstract]. Gastroenterology. 1997;112:A836.
  8. 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.
  9. Harris WS. N-3 fatty acids and serum lipoproteins: human studies. Am J Clin Nutr. 1997;65(suppl):1645S-1654S.
  10. Stuglin C, Prasad K. Effect of flaxseed consumption on blood pressure, serum lipids, hemopoietic system and liver and kidney enzymes in healthy humans. J Cardiovasc Pharmacol Ther. 2005;10:23-27.
  11. Wendland E, Farmer AJ, Paul G, et al. Effect of alpha-linolenic acid on cardiovascular risks markers: a systematic review. Heart. 2005 May 12. [Epub ahead of print]
  12. Hallund J, Ravn-Haren G, Bugel S, et al. A lignan complex isolated from flaxseed does not affect plasma lipid concentrations or antioxidant capacity in healthy postmenopausal women. J Nutr. 2005;136:112-116.
  13. Harper CR, Edwards MC, Jacobson TA. Flaxseed oil supplementation does not affect plasma lipoprotein concentration or particle size in human subjects. J Nutr. 2006;136:2844-2848.
  14. Zhang W, Wang X, Liu Y, et al. Dietary flaxseed lignan extract lowers plasma cholesterol and glucose concentrations in hypercholesterolaemic subjects. Br J Nutr. 2007 Dec 6.
  15. Bloedon LT, Balikai S, Chittams J, et al. Flaxseed and cardiovascular risk factors: results from a double blind, randomized, controlled clinical trial. J Am Coll Nutr. 2008;27:65-74.
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Some but not all human studies have found that flaxseed improves cholesterol profile.96 However, the benefits, if they do exist, are very modest. For example, in a double-blind study of about 200 postmenopausal women, use of flaxseed at a dose of 40 g daily produced measurable improvements in cholesterol profile, but the improvements were so small that the researchers considered them "clinically insignificant."94 It has been claimed that flaxseed might also have a direct effect in helping to prevent atherosclerosis based on its lignan ingredients, but the evidence upon which these claims are based is limited to studies in rabbits.95

Inconsistent evidence hints that flaxseed might reduce LDL cholesterol and, overall, slow down atherosclerosis.95,96,98-100,157,208,284 Flaxseed oil may be helpful as well, although evidence is again inconsistent.209,242

It may be the generic fiber and not the other specific ingredients in flaxseed that benefit cholesterol levels.97,184 Studies of purified lignans (found in flaxseed) have yielded mixed results.210,269

... (more)
  1. Dodin S, Lemay A, Jacques H, Légaré F, Forest JC, Mâsse B. The effects of flaxseed dietary supplement on lipid profile, bone mineral density, and symptoms in menopausal women: a randomized, double-blind, wheat germ placebo-controlled clinical trial. J Clin Endocrinol Metab. 90(3):1390-7.
  2. Prasad K. Dietary flax seed in prevention of hypercholesterolemic atherosclerosis. Atherosclerosis. 1997;132:69-76.
  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;18:1203-1214.
  4. Singer P, Jaeger W, Berger I, et al. Effects of dietary oleic, linoleic, and alpha-linolenic acids on blood pressure, serum lipids, lipoproteins and the formation of eicosanoid precursors in patients with mild essential hypertension. J Hum Hypertens. 1990;4:227-233.
  5. Prasad K. Reduction of serum cholesterol and hypercholesterolemic atherosclerosis in rabbits by secoisolariciresinol diglucoside isolated from flaxseed. Circulation. 1999;99:1355-1362.
  6. 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;69:395-402.
  7. Tarpila S, Kivinen A. Ground flaxseed is an effective hypolipidemic bulk laxative [abstract]. Gastroenterology. 1997;112:A836.
  8. 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.
  9. Harris WS. N-3 fatty acids and serum lipoproteins: human studies. Am J Clin Nutr. 1997;65(suppl):1645S-1654S.
  10. Stuglin C, Prasad K. Effect of flaxseed consumption on blood pressure, serum lipids, hemopoietic system and liver and kidney enzymes in healthy humans. J Cardiovasc Pharmacol Ther. 2005;10:23-27.
  11. Wendland E, Farmer AJ, Paul G, et al. Effect of alpha-linolenic acid on cardiovascular risks markers: a systematic review. Heart. 2005 May 12. [Epub ahead of print]
  12. Hallund J, Ravn-Haren G, Bugel S, et al. A lignan complex isolated from flaxseed does not affect plasma lipid concentrations or antioxidant capacity in healthy postmenopausal women. J Nutr. 2005;136:112-116.
  13. Harper CR, Edwards MC, Jacobson TA. Flaxseed oil supplementation does not affect plasma lipoprotein concentration or particle size in human subjects. J Nutr. 2006;136:2844-2848.
  14. Zhang W, Wang X, Liu Y, et al. Dietary flaxseed lignan extract lowers plasma cholesterol and glucose concentrations in hypercholesterolaemic subjects. Br J Nutr. 2007 Dec 6.
  15. Bloedon LT, Balikai S, Chittams J, et al. Flaxseed and cardiovascular risk factors: results from a double blind, randomized, controlled clinical trial. J Am Coll Nutr. 2008;27:65-74.
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It has been suggested that flaxseed might help reduce cholesterol and slow the progression of atherosclerosis. There are at least three flaxseed components with potential health benefits:

  • The first is fiber, which probably helps lower cholesterol.
  • Flaxseed also contains alpha-linolenic acid, a type of omega-3 fatty acid similar to the omega-3 fatty acids found in fish oil, but significantly different in other ways, and perhaps offering some of the same benefits. The omega-3 fatty acids in fish oil (and krill oil) probably help reduce high cholesterol and high triglycerides.
  • Finally, substances called lignans in flaxseed have phytoestrogenic properties making them somewhat similar to the isoflavones in soy, which has been found to be beneficial for treating high cholesterol and high triglycerides.
... (more)

Some but not all human studies have found that flaxseed improves cholesterol profile.96 However, the benefits, if they do exist, are very modest. For example, in a double-blind study of about 200 postmenopausal women, use of flaxseed at a dose of 40 g daily produced measurable improvements in cholesterol profile, but the improvements were so small that the researchers considered them "clinically insignificant."94 It has been claimed that flaxseed might also have a direct effect in helping to prevent atherosclerosis based on its lignan ingredients, but the evidence upon which these claims are based is limited to studies in rabbits.95

Inconsistent evidence hints that flaxseed might reduce LDL cholesterol and, overall, slow down atherosclerosis.95,96,98-100,157,208,284 Flaxseed oil may be helpful as well, although evidence is again inconsistent.209,242

It may be the generic fiber and not the other specific ingredients in flaxseed that benefit cholesterol levels.97,184 Studies of purified lignans (found in flaxseed) have yielded mixed results.210,269

... (more)

Flaxseed and some of its components, flaxseed oil and lignans, have been studied as potential treatments for high cholesterol and atherosclerosis. Research evidence is mixed.

... (more)

It has been suggested that flaxseed might help reduce cholesterol and slow the progression of atherosclerosis. There are at least three flaxseed components with potential health benefits:

  • The first is fiber, which probably helps lower cholesterol.
  • Flaxseed also contains alpha-linolenic acid, a type of omega-3 fatty acid similar to the omega-3 fatty acids found in fish oil, but significantly different in other ways, and perhaps offering some of the same benefits. The omega-3 fatty acids in fish oil (and krill oil) probably help reduce high cholesterol and high triglycerides.
  • Finally, substances called lignans in flaxseed have phytoestrogenic properties making them somewhat similar to the isoflavones in soy, which has been found to be beneficial for treating high cholesterol and high triglycerides.
... (more)