Flax (Linum usitatissimum) has been cultivated throughout the course of history and is still a major farm crop in Russia, Canada, and the northern plains of the United States. The flax plant has an erect stem that branches outward at the top, with pale green, spearhead-shaped leaves. Flax grows to a height of 20 inches and flowers from June through August, bearing small, light-blue flowers that wither quickly after opening in the morning. The mature plant produces a spherical pod that contains ten brown seeds, each approximately 1/4 inch long. The fibers of the plant are used to make linen. The seeds are pressed to extract flaxseed oil (also known as linseed oil), which is used to make linoleum and oil-based paints and is also consumed for health purposes. The health benefits of flaxseed oil are primarily attributed to its fatty acid profile. Flaxseed oil not only contains linoleic acid (an omega-6 essential fatty acid found in most vegetable oils), it is also a rich source of alpha linolenic acid, an omega-3 oil with many useful functions in the body. In addition to its essential fatty acid content, flaxseed oil contains unique compounds known as lignans. The two primary lignans in flaxseed are matairesinol and secoisolariciresinol-diglycoside. These compounds are converted by intestinal bacteria into the mammalian lignans enterodiol (from secoisolariciresinol-diglycoside) and enterolactone (from matairesinol). These lignans have weakly estrogenic and antiestrogenic activities and may play a role in estrogen-related health concerns such as menopause and PMS.
The amount of omega-3 oils needed in the body depends on the intake of other fats. The typical "Western" diet is high in omega-6 fatty acids and low in omega-3 oils. Many nutrition experts recommend one tablespoon of flaxseed oil per day, which can be added to salads or vegetables. The oil is also sold in softgel form, and many people find this form most convenient. Flaxseed oil should not be used in cooking because heat destroys alpha-linolenic acid. Flaxseed oil is very well tolerated, and no toxicity has been reported.