The Use of Dietary Flaxseed for the Prevention of Human Disease
by Kelly Weaver
Flaxseed (also called linseed) has been a part of the human and animal diet for thousands of years. It is the richest known plant source of omega-3 fatty acids - 58% of the total fat in flax is composed of alpha-linolenic acid (LNA); however, this fatty acid is a short chain omega-3 as opposed to the long chain omega 3s found in fish oil. A number of studies have shown that flaxseed does not replace fish oil in the diet because the conversion of LNA to the omega-3 fatty acids found in fish oil is very inefficient.
Flaxseed is also a minor source of the omega-6 fatty acid linoleic acid (LA), which makes up about 14% of the total fat content. LNA and LA are essential fatty acids, meaning they cannot be made in the body and instead must be present in the diet. LNA is thought to be necessary for the proper function of cell membranes and nerve cells. In addition to LNA, flaxseed also contains soluble and insoluble fiber and lignans, which are antioxidants and estrogen precursors called phytoestrogens.
Flaxseed provides a healthy balance of omega-3 and omega-6 fatty acids, which is thought to have beneficial effects on many diseases, especially those with a strong inflammatory component, such as inflammatory bowel disease, arthritis, asthma, gout, and lupus. Flaxseed oil has been used to treat burns, acne, eczema, rosacea, and other skin disorders, and it promotes healthy hair and nails. Flaxseed has been suggested to minimize nerve damage in degenerative diseases such as Parkinson's disease and may guard against the effects of aging.
The lignans in flaxseed may also play a role in cancer treatment and prevention, especially in women with breast cancer. The phytoestrogens found in flaxseed are thought to act as "designer estrogens" and are a good supplement to regular therapy (1). In a study of women with breast cancer, those who consumed 25 grams of flaxseed oil per day saw a reduction in tumor growth compared to placebo controls (2). The LNA in flaxseed may decrease the risk of sudden cardiac death by stabilizing the electrical system of the heart and preventing potentially fatal irregularities in heart rhythm. In a study of more than 75,000 women, those who consumed more than 1.5 grams of flaxseed per day had a 46% lower risk of cardiac death than women who consumed less than 0.5 grams per day (3).
While most studies show a benefit of flaxseed oil, there have been studies which have not been positive. In 5 out of 6 epidemiological studies on prostate cancer, flaxseed was shown to increase cancer risk, and LNA is a strong growth stimulus in isolated prostate cancer cells (4). Neither of these effects has been seen with fish oil. In addition, recent studies suggest that flaxseed may increase the risk of macular degeneration or speed up the progression of the disease.
Flaxseed is available as whole seeds, ground seeds, or oil, but due to processing, the oil may contain less lignans and fiber than the seeds. The recommended dose of flaxseed oil is one tablespoon of liquid oil per day or two 3,000 mg capsules per day. Flaxseed may slow down the absorption of oral medications if taken at the same time. Flaxseed may also interact with medications such as blood thinners, statins, cyclosporine, and NSAIDS. It is important to consult a healthcare provider before using flaxseed while taking these medications.
Literature cited.
- Moyer, Paula. A Muffin a Day for Breast Cancer? 2000 December 8. WebMD. http://www.webmd.com/content/article/29/1728_66150.htm
- Clin Cancer Res. 2005 May 15;11(10):3828-35
- Peck, Peggy. Flaxseed May Lower Sudden Cardiac Death Risk. 2004 November 8. WebMD http://www.webmd.com/content/article/96/103889.htm
- WebMD. Ask Dr. Ornish. http://www.webmd.com/content/pages/3/3079_1820.htm