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.
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For over a decade, our team has combed through thousands of research articles published in reputable journals. To help you make educated decisions, and to better understand controversial or confusing supplements, our medical experts have digested the science into these three easy-to-follow ratings. We hope this provides you with a helpful resource to make informed decisions towards your health and well-being.
3 StarsReliable and relatively consistent scientific data showing a substantial health benefit.
2 StarsContradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
1 StarFor an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support.
This supplement has been used in connection with the following health conditions:
1 Tbsp (15 ml) whole or ground with a full glass of water, one or two times per day
Flaxseed is a mild bulk-forming laxative that’s best suited for long-term use in people with constipation.
The laxatives most frequently used world-wide come from plants. Herbal laxatives are either bulk-forming or stimulating. Bulk-forming laxatives come from plants with a high fiber and mucilage content that expand when they come in contact with water; examples include psyllium, flaxseed, and fenugreek. As the volume in the bowel increases, a reflex muscular contraction occurs, stimulating a bowel movement. These mild laxatives are best suited for long-term use in people with constipation.1
Hypertension and Atherosclerosis
Refer to label instructions
In a double-blind trial, eating foods with milled flaxseed lowered both the systolic and diastolic blood pressure in patients with atherosclerosis of the lower extremities.
In a double-blind trial, patients with atherosclerosis of the lower extremities (most of whom had high blood pressure) consumed foods that provided daily 30 g of milled flaxseed or placebo foods for 6 months. After 6 months, mean systolic blood pressure was 9.4 mm Hg lower and mean diastolic blood pressure was 6.7 mm Hg lower in the flaxseed group than in the placebo group.2 It is not known whether flaxseed would have a similar effect in people who do not have atherosclerosis.
2 tablespoons of flaxseeds twice per day
Supplementing with flaxseeds may improve the frequency and severity of hot flashes in postmenopausal women.
In a preliminary trial, supplementation with crushed flaxseeds for six weeks improved the average hot flash score (a measure of the frequency and severity of hot flashes) by 57% in postmenopausal women who were not receiving estrogen therapy. The treatment consisted of 2 tablespoons of flaxseeds (along with at least 10 ounces of liquid) twice a day. About one-fifth of the women discontinued treatment because of abdominal symptoms or other side effects.3 In a double-blind trial, daily consumption of 25 g of partially defatted ground flaxseed significantly decreased the number of hot flashes and improved overall menopausal symptoms. However, the improvements were not greater than those in women given a placebo (wheat bran).4 Because of these conflicting results, the effectiveness of flaxseed as a treatment for menopause remains uncertain.
Refer to label instructions
Flaxseed is an anti-inflammatory and soothing herb that may be effective in the treatment of ulcerative colitis.
Aloe vera juice has anti-inflammatory activity and been used by some doctors for people with UC. In a double-blind study of people with mildly to moderately active ulcerative colitis, supplementation with aloe resulted in a complete remission or an improvement in symptoms in 47% of cases, compared with 14% of those given a placebo (a statistically significant difference).5 No significant side effects were seen. The amount of aloe used was 100 ml (approximately 3.5 ounces) twice a day for four weeks. Other traditional anti-inflammatory and soothing herbs, including calendula, flaxseed, licorice, marshmallow, myrrh, and yarrow. Many of these herbs are most effective, according to clinical experience, if taken internally as well as in enema form.6 Enemas should be avoided during acute flare-ups but are useful for mild and chronic inflammation. It is best to consult with a doctor experienced with botanical medicine to learn more about herbal enemas before using them. More research needs to be done to determine the effectiveness of these herbs.
In a preliminary trial, people with UC significantly improved on a sugar-free, low-allergen diet with additional nutritional supplementation that included a multivitamin-mineral supplement (2–6 tablets per day); a fish oil supplement (400 mg per day); borage oil (400 mg per day); flaxseed oil (400 mg per day); and a probiotic formula containing Lactobacillus acidophilus and other species of beneficial bacteria.7 Some participants received slight variations of this regimen. Since so many different supplements were given and since the trial was not controlled, it is not possible to say which, if any, of the nutrients was responsible for the improvement observed by the researchers.
How It Works
How to Use It
For promoting bowel regularity, 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 alpha linolenic acid (ALA) to eicosapentaenoic acid (EPA) does occur,8 and this conversion can be increased by restricting the intake of other vegetable oils.9
For those who wish to replace fish oil with flaxseed oil, research suggests taking up to ten times as much ALA as EPA.10 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).
Where to Find It
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.
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.
Interactions with Supplements, Foods, & Other Compounds
At the time of writing, there were no well-known supplement or food interactions with this supplement.
Interactions with Medicines
As of the last update, we found no reported interactions between this supplement and medicines. It is possible that unknown interactions exist. If you take medication, always discuss the potential risks and benefits of adding a new supplement with your doctor or pharmacist.
The Drug-Nutrient Interactions table may not include every possible interaction. Taking medicines with meals, on an empty stomach, or with alcohol may influence their effects. For details, refer to the manufacturers’ package information as these are not covered in this table. If you take medications, always discuss the potential risks and benefits of adding a supplement with your doctor or pharmacist.
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,11, 12, 13, 14, 15 one animal study16 and a preliminary human study17 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.18 For prostate cancer, a test tube study reported ALA promoted cancer cell growth,19 but preliminary human studies have shown ALA to be associated with either an increased20, 21 or decreased risk,22 or no change23 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,24 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.25
Animal research suggests that large amounts of flaxseed or lignans consumed during pregnancy might adversely affect the development of the reproductive system.26 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.27, 28
Omega-3s Build Strong Bones
Supplement Safety Myths & Facts
1. Cockerell KM, Watkins AS, Reeves LB, et al. Effects of linseeds on the symptoms of irritable bowel syndrome: a pilot randomised controlled trial. J Hum Nutr Diet 2012;25:435-43. doi: 10.1111/j.1365-277X.2012.01263.x.
2. Rodriguez-Leyva D, Weighell W, Edel AL, et al. Potent antihypertensive action of dietary flaxseed in hypertensive patients. Hypertension 2013;62:1081–9.
3. Pruthi S, Thompson SL, Novotny PJ, et al. Pilot evaluation of flaxseed for the management of hot flashes. J Soc Integr Oncol 2007;5:106-12.
4. Simbalista RL, Sauerbronn AV, Aldrighi JM, Areas JAG. Consumption of a flaxseed-rich food is not more effective than a placebo in alleviating the climacteric symptoms of postmenopausal women. J Nutr 2010;140:293-7.
5. Langmead L, Feakins RM, Goldthorpe S, et al. Randomized, double-blind, placebo-controlled trial of oral aloe vera gel for active ulcerative colitis. Aliment Pharmacol Ther 2004;19:739-47.
7. Edman JS, Williams WH, Atkins RC. Nutritional therapies for ulcerative colitis: literature review, chart review study, and future research. Altern Ther Health Med 2000;6:55-63.
8. 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.
9. Mantzioris E, James MJ, Bibson RA, Cleland LG. Dietary substitution with an alpha-linolenic acid-rich vegetable oil increases eicosapentaenoic acid concentrations in tissues. Am J Clin Nutr 1994;59:1304-9.
10. 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.
11. 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.
12. 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.
13. 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.
14. 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.
15. Cave WT Jr. Dietary n-3 (omega-3) polyunsaturated fatty acid effects on animal tumorigenesis. FASEB J 1991;5:2160-6 [review].
16. Braden LM, Carroll KK. Dietary polyunsaturated fat in relation to mammary carcinogenesis in rats. Lipids 1986;21:285-8.
17. 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.
18. 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.
19. 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.
20. 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.
21. 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.
22. 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.
23. 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.
24. 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.
25. 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.
26. 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.
27. Alonso L, Marcos ML, Blanco JG, et al. Anaphylaxis caused by linseed (flaxseed) intake. J Allergy Clin Immunol 1996;98:469-70.
28. Leon F, Rodriguez M, Cuevas M. Anaphylaxis to Linum. Allergol Immunopathol (Madr) 2003;31:47-9.
The information presented in Aisle7 is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires June 2015.
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