Flax seed, or linseed (Linum usitatissimum L.), comes from the flax plant, which is an annual herb. The ancient Egyptians used flaxseed as both food and medicine. In the past, flaxseed was used mostly as a laxative. It is high in fiber and contains a gummy material called mucilage, both of which expand when they come in contact with water. They add bulk to stool and help it move more quickly through the intestines.

Flaxseed and flaxseed oil are rich in alpha-linolenic acid (ALA), an omega-3 fatty acid that may be helpful for heart disease, inflammatory bowel disease (IBD), arthritis, and other health problems. Other omega-3 fatty acids include those found in fish oil, which are docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Mackerel, salmon, and walnuts are good sources of omega-3 fatty acids.

Flaxseed oil contains only ALA, not the fiber or lignans found in the flaxseed. Other plants that contain ALA include canola (rapeseed), soybean oil, walnuts, and pumpkin seed. Studies suggest that flaxseed may help prevent and treat of the following health conditions.

High cholesterol

People who eat a Mediterranean diet tend to have higher HDL (good) cholesterol levels. The Mediterranean diet includes whole grains, root and green vegetables, fruits, fish and poultry, olive and canola oils, and ALA from flaxseed, flaxseed oil, and walnuts. It limits the amount of red meat, butter, and cream you eat.

In lab tests and animal studies, flaxseed and flaxseed oil have been reported to lower cholesterol. Human studies show mixed results. One human study found that people who added flaxseed to a low-cholesterol diet lowered their LDL (bad) cholesterol and triglyceride levels (fats in the blood).

Heart disease

A diet rich in fruits, vegetables, whole grains, nuts or legumes, and foods with ALA may reduce the risk of heart attack and stroke, both for people who have never had either problem and for those who have already had a heart attack or a stroke.

One of the best ways to help prevent and treat heart disease is to eat a diet low in saturated fat and trans fat, and eat foods that are rich in monounsaturated and polyunsaturated fats, including omega-3 fatty acids from flaxseed. Evidence suggests that people who eat an ALA-rich diet are less likely to have a fatal heart attack.

Several human studies suggest that a diet rich in omega-3 fatty acids (including ALA) may lower blood pressure in people with hypertension.

Menopausal symptoms

One small study compared flaxseed to hormone replacement therapy (HRT) in menopausal women. It reported that 40 g of flaxseed worked as well as HRT for mild menopausal symptoms (hot flashes, mood disturbances, and vaginal dryness). But the study was not well designed, and another, larger study found that flaxseed did not improve symptoms like hot flashes, nor did it protect against bone loss.

Breast cancer

Flaxseed contains phytoestrogens, which are plant chemicals called lignans. Because lignans may act like estrogen in the body, scientists aren't sure whether flaxseed would be harmful or helpful for breast cancer. Studies have reported that flaxseed reduced breast tumor growth and metastasis (spreading) in rats.

There has been only one clinical study in humans. In that study, postmenopausal women who were newly diagnosed with breast cancer ate a muffin with 25 grams dietary flaxseed every day for 40 days. The study found that adding flaxseed to the diet may have the potential to reduce tumor growth in women with breast cancer. More research is needed.

Colon cancer

Animal studies show that lignans may slow the growth of colon tumor cells. Population studies suggest that flaxseed may reduce the number of abnormal cell growths, which are early markers of colon cancer. Clinical trials in people are needed, however.

Prostate cancer

Results from studies are confusing when it comes to prostate cancer and flaxseed. A few studies seemed to show that ALA intake was associated with an increased risk for prostate cancer. But other studies have found that flaxseed may benefit men at risk for prostate cancer. In one study, men with a precancerous prostate condition called PIN had lower PSA levels (a marker of prostate cancer) when they ate 30 g of flaxseed daily along with a low-fat diet. In men who had prostate cancer, 30 g of flaxseed daily and a low-fat diet did not lower PSA levels. But it did appear to lower levels of testosterone and slow down the rate of tissue growth. More studies are needed to understand how flaxseed may affect prostate cancer.

Other uses

Researchers are investigating whether omega-3 fatty acids may help protect against certain infections and in treating conditions including ulcers, migraine headaches, attention deficit/hyperactivity disorder (ADHD), addiction, eating disorders, preterm labor, emphysema, psoriasis, glaucoma, Lyme disease, lupus, and panic attacks.