Flaxseeds are the hard, tiny seeds of Linum usitatissimum, the flax plant, which has been widely used for thousands of years as a source of food and clothing. There are at least three flaxseed components with potential health benefits. The first is fiber, valuable in treating constipation. Flaxseed also contains alpha-linolenic acid, a type of omega-3 fatty acid similar to the omega-3 fatty acids found in fish oil, but significantly different in other ways, and perhaps offering some of the same benefits. Finally, substances called lignans in flaxseed have phytoestrogenic properties making them somewhat similar to the isoflavones in soy.

The oil made from flaxseed has no appreciable amounts of lignans, but it does contain alpha-linolenic acid. See the articles on Flaxseed Oil and Lignans for more information on these substances.

The fiber in flaxseed binds with water, swelling to form a gel which, like other forms of fiber, helps soften the stool and move it along in the intestines. One study found that flaxseed can help with chronic constipation in irritable bowel disease.2Germany's Commission E authorizes the use of flaxseed for various digestive problems, such as chronic constipation, irritable bowel syndrome, diverticulitis, and general stomach discomfort.1

Flaxseed may be slightly helpful for improving cholesterol profile, according to some but not all studies.3-5,60-62,72Purified alpha linolenic acid or lignans alone have not consistently shown benefits.63-64 It may be the generic fiber and not the other specific ingredients in flaxseed that benefit cholesterol levels.

Flaxseed, its lignans, and its oil have undergone a small amount of investigation for potential cancer preventionor cancer treatment possibilities.11-18

Flaxseed has shown some promise for treating kidney disease associated with lupus(lupus nephritis).20-21

Because it is believed to have soothing properties, flaxseed is sometimes used for symptomatic relief of stomach distressand applied externally for inflammation of the skin.22 However, research on these potential uses is essentially nonexistent.

Although flaxseed is often advocated for the treatment of symptoms related to menopause, a sizable 12-month study failed to find it more helpful than wheat germ placebo.61Besides failing to improve immediate symptoms such as hot flashes, flaxseed did not appear to provide any protection against loss of bone density. A previous, much smaller study by the same researchers found it equally effective for menopausal symptoms as hormone replacement therapy, but due to the absence of a placebo group and the high rate of placebo response in menopausal symptoms, these results cannot be taken as indicating much.60Another study tested flaxseed without comparing it to placebo and reported a 50% reduction in hot flashes.66 The researchers went on to state that this reduction in hot flashes was “greater than what would be expected with placebo,” a rather curious claim since because menopauseal women given placebo typically experience almost exactlya 50% decrease in hot flashes.67

In a preliminary double-blind trial of 78 older men, flaxseed extract modestly improved the urinary symptoms associated with benign prostatic hyperplasia(prostate enlargement) after four months of treatment.70

Use of essential fatty acids in the omega-3 family has also shown some promise for the treatment of non-alcoholic fatty liver.69Based on a small, randomized study, flaxseed may also decrease levels of certain liver enzymes, possibly reducing the risk of liver disease in men who have high cholesterol.72