Flaxseed is the seed of the flax plant, which is believed to have originated in Egypt. It grows throughout Canada and the northwestern United States. Flaxseed oil comes from flaxseeds.
Common Names—flaxseed, linseed
Latin Names—Linum usitatissimum
What Flaxseed Is Used For
Flaxseed is most commonly used as a laxative.
Flaxseed is also used for hot flashes and breast pain.
Flaxseed oil is used for different conditions than flaxseed, including arthritis.
Both flaxseed and flaxseed oil have been used for high cholesterol levels and in an effort to prevent cancer.
How Flaxseed Is Used
Whole or crushed flaxseed can be mixed with water or juice and taken by mouth. Flaxseed is also available in powder form. Flaxseed oil is available in liquid and capsule form. Flaxseed contains lignans (phytoestrogens, or plant estrogens), while flaxseed oil preparations lack lignans.
What the Science Says
Flaxseed contains soluble fiber, like that found in oat bran, and may have a laxative effect.
Studies of flaxseed preparations to lower cholesterol levels report mixed results. A 2009 review of the clinical research found that cholesterol-lowering effects were more apparent in postmenopausal women and in people with high initial cholesterol concentrations.
Some studies suggest that alpha-linolenic acid (a substance found in flaxseed and flaxseed oil) may benefit people with heart disease. But not enough reliable data are available to determine whether flaxseed is effective for heart conditions.
Study results are mixed on whether flaxseed decreases hot flashes.
Although some population studies suggest that flaxseed might reduce the risk of certain cancers, there is not enough research to support a recommendation for this use.
NCCAM is funding studies on flaxseed. Recent studies are looking at its potential role in preventing or treating atherosclerosis (hardening of the arteries), breast cancer, and ovarian cysts.
Side Effects and Cautions
Flaxseed and flaxseed oil supplements seem to be well tolerated. Few side effects have been reported.
Flaxseed, like any supplemental fiber source, should be taken with plenty of water; otherwise, it could worsen constipation or, in rare cases, even cause intestinal blockage. Both flaxseed and flaxseed oil can cause diarrhea.
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 any conventional oral medications or other dietary supplements.