Flaxseed is an oil seed (also called linseed) and was used to make fabric, called linen. Flaxseed contains 41% fat, 28% fiber, and 21% protein.
Flaxseed has been used for constipation and dry, itching skin.
Flaxseeds and ground flaxseed contain three important components: alpha-linolenic acid, soluble fiber, and lignans. Flaxseed is the richest known source of the lignan secoisolariciresinol diglucoside (SDG), the main mammalian lignan precursor.
Flaxseed oil is rich in polyunsaturated fatty acids, and is the richest known source of alpha-linolenic acid, one of the omega-3 (n-3) fatty acids. Flaxseed oil does not contain fiber or lignans.
Alpha-linolenic acid and lignans may have chemopreventive actions.
Alpha-linolenic acid (ALA) is converted to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). EPA is a precursor for the series-3 prostaglandins, the series-5 leukotrienes, and the series-3 thromboxanes.
EPA and DHA modify cell membrane fluidity and the products of EPA (prostaglandins, leukotrienes, and thromboxanes) have anti-inflammatory and anti-thrombotic activities.
The n-3 fatty acids are important for development of an infant’s brain and retina, and are thus essential during pregnancy and breastfeeding.
Flaxseeds, ground flaxseed, crushed flaxseeds, and flaxseed oil are available. These different forms have slightly different activities, due to differences in bioavailability and content. Ground or crushed seeds have higher bioavailability than whole flaxseeds. Flaxseed oils have higher concentrations of lignans and alpha-linolenic acid, but do not contain fiber.
Patients taking anticoagulant agents, such as warfarin (Coumadin), may experience abnormal bleeding. Patients may benefit by starting the medication at a lower dose with concomitant ingestion of flaxseed oil, and those with a bleeding disorder should consult a physician or pharmacist before starting the therapy.
Information on the relationship between substances and disease is provided for general information, in order to convey a balanced review of the scientific literature. In many cases the relationship between a substance and a disease is tentative and additional research is needed to confirm such a relationship.
High-oleic rapeseed (canola) and flaxseed oils modulate serum lipids and inflammatory biomarkers in hypercholesterolaemic subjects.
A randomized crossover study examined the effects of flaxseed and canola oils on serum lipids and inflammation markers in people with elevated total cholesterol (TC) levels. For 28 days, 36 participants consumed each of 3 diets with ~36% energy from fat; 70% of the fat was high-oleic canola oil (HOC), flaxseed oil blended with canola oil (F+C), or typical Western diet fats (fat content of saturated, mono- and polyunsaturated n-6 and n-3 was 6, 23, 5, 1% energy for high-oleic canola oil; 6, 16, 5, 7.5% energy for flaxseed blended with canola oil; 11.5, 16, 6, 0.5% energy for Western diet fats). LDL-cholesterol was reduced 15.1% (P<0.01) with F+C and 7.4% (P<0.01) with HOC, versus Western diet fats. Similarly, TC was reduced 11% (P<0.01) with F+C and 3.5% (P<0.01) with HOC compared to the Western diet fats; TC was different between F+C and HOC groups at the end of the trial (P<0.05). HDL-cholesterol was reduced by 8.5% (P<0.01) and LDL:HDL ratio was reduced by 7.5% (P<0.01) in the F+C group versus the Western diet. F+C decreased E-selectin concentration compared with the Western diet (P=0.02). These results suggest that flaxseed blended with canola oil improved blood lipid parameters and possibly inflammation. Canola oil alone also improved blood lipid parameters but less than the flaxseed oil blend. Further studies are necessary to investigate these results.4
Dietary supplementation with flaxseed oil lowers blood pressure in dyslipidaemic patients.
A prospective, two-group, parallel-design study investigated flaxseed oil and safflower oil on blood pressure in people with elevated blood lipids. Participants consumed flaxseed oil supplements (supplying 8 g/day alpha linolenic acid; n=59) or safflower oil supplements (supplying 11 g/day linoleic acid; n=28) for twelve weeks. Blood pressure was measured at baseline and at the end of the supplementation period. Flaxseed oil supplements were associated with significantly lower systolic and diastolic blood pressure levels (P=0.016 and P=0.011, respectively) compared to safflower oil. This study suggests that flaxseed oil supplements may lower blood pressure; further trials are needed to investigate the mechanisms underlying these results.5
Flaxseed improves lipid profile without altering biomarkers of bone metabolism in postmenopausal women.
To examine the effect of ground flaxseed on lipid metabolism and biomarkers of bone metabolism, thirty-six postmenopausal women consumed 40 grams of ground flaxseed or a placebo daily for three months along with 1000 mg calcium and 400 IU vitamin D. Women receiving hormone replacement therapy were excluded from the study. Flaxseed supplementation significantly decreased total and non HDL cholesterol concentrations by 6%. LDL and HDL cholesterol concentrations were reduced by 4.7% and reduced triglyceride concentrations by 12.8% although these reductions were not significant. These results indicate that flaxseed reduced risk factors for cardiovascular diseases, but did not alter biomarkers of bone metabolism.6
The effects of flaxseed dietary supplement on lipid profile, bone mineral density, and symptoms in menopausal women: a randomized, double-blind, placebo-controlled clinical trial.
One-hundred-ninety-nine menopausal women participated in a double-blind clinical trial to assess the effects of ground flaxseed on blood lipid profiles, bone mineral density, and symptoms of menopause. Subjects consumed 40 grams/day of ground flaxseed or a placebo for 12 months. Total and HDL cholesterol decreased significantly in the ground flaxseed group compared to placebo. No changes in bone mineral density were detected. The authors concluded that ground flaxseed supplements improved blood lipid profiles, but not enough to be clinically significant.7
Flaxseed oil increases the plasma concentrations of cardioprotective (n-3) fatty acids in humans.
Fifty-six chronically ill people were randomly assigned to receive either 3 grams/day of alpha-linolenic acid from flaxseed oil or an olive oil placebo for 12 weeks. Plasma concentrations of EPA increased by 60% and plasma concentrations of DPA increased by 25% after 12 weeks. No change in DHA was detected in either group. These data indicate that flaxseed oil may be a useful substitute for fish oil supplements for improving plasma concentrations of cardioprotective fatty acids.8
Topic: American Heart Association Scientific Statement
Fish consumption, fish oil, omega-3 fatty acids, and cardiovascular disease.
In 2002, the American Heart Association (AHA) updated its recommendations regarding omega-3 fatty acids and cardiovascular disease. In this new statement, the benefits of omega-3 fatty acids are reviewed and flaxseeds as well as flaxseed oil are recommended to increase daily intake of alpha-linolenic acid. Thus, the AHA concluded that the current scientific data support including fish, fish oil, and omega-3 fatty acids from sources such as flaxseeds to reduce risk for cardiovascular disease.9
Supplementation with flaxseed oil versus sunflower seed oil in healthy young men consuming a low fat diet: effects on platelet composition and function.
Eleven healthy young subjects were given either flaxseed oil (40 g/day) or sunflower seed oil for 23 days and platelet aggregation was measured. Platelets from the flaxseed oil group were rich in EPA, compared to the control group. Aggregation response induced by 0.75 and 2 mcg of collagen was decreased in the flaxseed oil-fed group. The authors suggested that ingesting flaxseed oil may protect against cardiovascular disease through decreased platelet aggregation.10
Supplementing lactating women with flaxseed oil does not increase docosahexaenoic acid in their milk.
Seven lactating mothers between the ages of 28 and 39 years old were given 20 g of flaxseed oil per day (10.7 g ALA) for a period of four weeks. ALA and DPA concentrations were found to significantly increase in breast milk, plasma, and erythrocytes. EPA concentrations were found to increase significantly in breast milk and plasma. No changes in DHA concentrations were detected. Flaxseed oil supplementation, while significantly increasing ALA, DPA, and EPA concentrations in breast milk, is not a way to increase DHA concentrations in breast milk.11
Supplementation with flaxseed alters estrogen metabolism in postmenopausal women to a greater extent than does supplementation with an equal amount of soy.
Forty-six postmenopausal women were randomly assigned to receive either 25 grams ground flaxseed, 25 grams soy flour, or a placebo daily for 16 weeks to evaluate the effects of these supplements on estrogen metabolism. Flaxseed supplementation, but not soy flour or placebo, increased urinary excretion of 2-hydroxyestrone, a primary metabolite of estrogen. Excretion of 16 alpha-hydroxyestrone, another major metabolite of estrogen was not changed in any group. The ratio of 2-hydroxyestrone to 16 alpha-hydroxyestrone was positively correlated to the levels of urinary lignan. The authors cautiously suggest that ground flaxseed may have beneficial effects on estrogen metabolism for postmenopausal women.12
Dietary flaxseed alters tumor biological markers in postmenopausal breast cancer.
Thirty-two postmenopausal women with diagnosed breast cancer participated in a study of the effects of dietary flaxseed on breast cancer. Subjects received either 25 grams/day of flaxseed (19 subjects) or a placebo (13 subjects) from the date of diagnosis to the date the tumor was surgically removed, approximately 35 days. Consumption of flaxseed increased tumor cell death (apoptosis) and decreased biomarkers of tumor cell growth. These results suggest that flaxseed may help reduce tumor growth in women with breast cancer.13
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