Flaxseed is the seed of the plant Linum usitatissimum. It is a rich source of alpha-linolenic acid (ALA), an omega-3 fatty acid that is an essential nutrient in the human diet. Flaxseed also contains linoleic acid (LA), an essential omega-6 fatty acid, and is rich in dietary fiber and lignans, a class of phytonutrients. Flaxseed oil is a vegetable oil derived from pressed flaxseed. Flaxseed and flaxseed oil have different properties and nutritional values.
Flaxseed is most commonly used as a laxative, according to the National Center for Complementary and Alternative Medicine (NCCAM). This use is related to the fiber content of the seed. Due to the estrogen-like properties of lignans, it is also used as a treatment for hot flashes related to menopause and relief of breast pain. Flaxseed oil does not contain fiber or lignans, and it is used for conditions including the treatment of rheumatoid arthritis. Due to its omega-3 fatty acid content, flaxseed is sometimes taken as a supplement to help lower cholesterol and reduce the risk of heart disease. Evidence supports the use of flaxseed in lowering total cholesterol in people with high cholesterol and reducing menopause symptoms, but additional research is needed regarding the effectiveness of all other uses.
L. usitatissimum is a slender plant with narrow leaves and blue flowers that grows anywhere from 8–45 in. (20–130 cm) tall. The plant originated in India but has been farmed across the world for thousands of years. Archaeologists discovered evidence that flax was cultivated in ancient Babylon as early as 3000 BC.
Flax is grown for both consumption and industrial use. The seed is about 42% oil. Solvent-extracted oil from flax seeds is used for industrial purposes and is often called linseed oil. It is used in manufacturing oil paints, varnishes, and linoleum. The material that remains after oil has been extracted from the seeds is called linseed cake or linseed meal. It is often added to animal feed as a protein and omega-3 fatty acid supplement. Omega-3 enriched eggs, for example, come from chickens fed flax. Omega-3 enriched pork is available in countries including the United States, Canada, and Japan.
Human consumption of flaxseed and flaxseed oil has increased substantially since the mid-1990s. Flaxseed oil for human consumption is produced through solvent-free cold pressing at low temperatures. Bottled flaxseed oil can be used to make salad dressing or added to already cooked foods. Flaxseed oil should not be used to fry food, however, because the oil cannot withstand high temperatures. Flaxseed oil is also sold in capsule form as a dietary supplement. Flaxseeds come in brown, golden, and yellow varieties and have a slightly nutty flavor. Seeds are sold whole or are ground (milled) for consumption. Flaxseed flour, also called flaxseed meal or flaxmeal, is used in baking.
Flaxseed is rich in fiber, omega-3 fatty acids, and lignans. According to the Flax Council of Canada, 1 Tbsp. (14.3 g) of ground flaxseed provides about 36 calories, 1.8 g of ALA, 1.6 g of protein, and 2.2 g of dietary fiber. One tsp. (4.5 mL) of flax oil provides 44 calories and 2.8 g of ALA, but contains no protein or fiber. The oil in flaxseed is high in polyunsaturated fat (a healthy fat) and contains no trans fat or cholesterol. Flaxseed also provides vitamins C, E, K, B1 (thiamin), B2 (riboflavin), and B6, along with the minerals calcium, iron, magnesium, phosphorous, zinc, copper, manganese, and selenium. Flaxseed is low in sodium and carbohydrates.
FIBER. Flaxseed, both whole and ground, contains dietary fiber. Fiber helps promote satiety and prevent constipation. Ground flax is preferred over whole seeds because it is easier to digest. If the seed is not broken down during digestion, the person will not obtain the health benefits of the seed. Flaxseed oil does not contain fiber.
POLYUNSATURATED FATTY ACIDS. According to the Flax Council of Canada, about 42% of the flaxseed is oil and more than 70% of that oil is polyunsaturated fat (PUFA). Of that fat content, 57% is ALA. PUFAs and monounsaturated fats are unsaturated fats, healthy fats that may help reduce blood cholesterol levels. Omega-6 is also a polyunsaturated fat, and flaxseed contains about 17% of this fat in the form of linolenic acid.
LIGNANS. Flaxseed is the richest dietary source of plant lignans, compounds found in plants that mimic the effect of estrogen. There are 85.5 mg of lignans in 1 oz. (28.35 g) of flaxseeds, according to the Linus Pauling Institute at Oregon State University. Lignans compete with estrogen for binding sites on cells. They may help alleviate symptoms of menopause by simulating estrogen response in the body.
Flaxseed is available in several forms: as whole seeds, ground flaxseed, flax meal, and flax oil. Whole seeds can be stored at room temperature for up to one year, and ground seeds can be kept in an airtight container in the refrigerator for up to three months. When ground flax is needed, it is preferable to grind whole seeds in a coffee grinder, blender, or food processor immediately before use.
According to the Mayo Clinic, ground seeds are preferred, because the body cannot break down the whole seeds to access the omega-3 oil. Ground flaxseed can be added to several foods, such as oatmeal, condiments, and baked goods. Flaxseed oil can be used to make salad dressing or added as an ingredient to food that is already cooked. Bottled flaxseed oil should be stored in the refrigerator to avoid the breakdown of the chemicals. Flaxseed oil supplements, which come in capsule form, usually range in strength from 1,000 to 1,300 mg.
According to the National Center for Complementary and Alternative Medicine (NCCAM), flaxseed may produce a laxative effect and may reduce cholesterol in postmenopausal women and people with high cholesterol. As of 2018, the NCCAM was funding additional studies on the potential role of flaxseed in preventing or treating atherosclerosis (hardening of the arteries), breast cancer, and ovarian cysts. While some studies showed that the omega-3 in fish and fish oil helped to reduce inflammation, more research was needed about the use of flaxseed for this treatment.
Flaxseed has also been studied as a potential treatment or deterrent for heart disease, rheumatoid arthritis, and cancer. However, there is not enough evidence that flaxseed helps treat or prevent any of these conditions.
MENOPAUSE. Ground flaxseed may help with symptoms of menopause such as hot flashes and night sweats. Menopause is defined as the time when a woman's menstrual periods stop, and menopause is the most common hormonal condition that causes hot flashes. Characterized by a sudden feeling of warmth, hot flashes are usually most intense around the face, neck, and chest, according to the Mayo Clinic. The skin may redden, and the woman may sweat profusely and then feel chilled. A woman may experience these symptoms several times a week or several times a day. When the symptoms occur at night, sleep is disrupted. In order to provide relief, 40g of flaxseed must be consumed per day.
People should discuss supplement intake with their physician before adding any supplements to their diet. This is especially important for women who are pregnant or breastfeeding and for people with chronic conditions such as cancer. Parents should also discuss the use of supplements for their children. Dietary supplements do not undergo the same scrutiny as prescription medications. The U.S. Food and Drug Administration (FDA) does not require supplement manufacturers to prove that their products are safe and effective as long as the manufacturer does not make claims that the product can prevent, treat, or cure a specific disease.
Due to its fiber content, flaxseed should be taken with water, according to NCCAM. Too much fiber without water can lead to constipation or, in rare cases, intestinal blockage. Flaxseed can cause diarrhea.
Although flaxseed contains omega-3 fatty acids, fish is a richer source of the nutrient, according to the American Heart Association (AHA). The AHA recommends that people consume fish at least twice a week, especially fatty fish such as salmon, tuna, albacore tuna, and mackerel. Omega-3 fatty acids are thought to decrease triglyceride levels, prevent heart disease, and lower blood pressure.
The fiber in flaxseed may lower the body's ability to absorb medications that are taken by mouth. Flaxseed should not be taken at the same time as other medications or other dietary supplements without first consulting with a physician. Drugs that might interact with flaxseed include acetaminophen, antibiotic drugs, oral contraceptives, and diabetes medications, ibuprofen, aspirin, blood-thinning drugs such as warfarin (Coumadin), blood pressure medications, and herbal remedies.
Complications are unlikely to occur when flax products are used to meet daily dietary needs. Some studies have found a link between ALA and increased risk of prostate cancer, but other studies have found that flaxseed may reduce the risk of prostate cancer. Men who are at risk for prostate cancer may wish to consult with a physician before consuming flaxseed.
Parents should be aware that a safe dosage of flaxseed supplements has not been established. They should consult with their child's pediatrician about recommended intake of flaxseed.
See also Cancer-fighting foods ; Constipation ; Dietary supplements ; Menopause diet .
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Tish Davidson, AM
Revised by Liz Swain