Flaxseed or linseed (Linum usitatissimum L.) comes from the flax plant, an annual herb. The ancient Egyptians used flaxseed as both food and medicine. They also used the fiber from the flax plant to make clothes, fishnets, and other products. Historically, flaxseed has been primarily used as a laxative. It is high in fiber and a gummy material called mucilage. These substances expand when they come in contact with water, so they add bulk to stool and help it move more quickly through the gastrointestinal tract.
The seeds and oil of the flax plant also contain substances that are healthy. 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, arthritis, and a variety of other health problems. Other plants that provide ALA include canola (rapeseed), soybean oil, walnuts, and pumpkin seed.
It is important to maintain a good balance of omega-3 and omega-6 -- another essential fatty acid -- in your diet, as these two substances work together to promote health. Mackerel, salmon, and walnuts are also good sources of omega-3 fatty acids. Other omega-3 fatty acids include those found in fish oil (docosahexaenoic acid or DHA, and eicosapentaenoic acid or EPA).
Flaxseed oil contains only ALA part of flaxseed, not the fiber or lignans in the seed. Studies suggest that flaxseed may play a role in the prevention and treatment of the following health conditions:
People who eat a Mediterranean diet tend to have higher HDL ("good") cholesterol levels. The Mediterranean diet has a healthy balance of omega-3, omega-6, and omega-9 (found in olive oil) fatty acids. It 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.
In lab tests and animal studies, flaxseed and flaxseed oil have been reported to lower cholesterol. Human studies have had mixed results. One human study found that people who added flaxseed to a low-cholesterol diet lowered their LDL ("bad") cholesterol and triglycerides (fats in the blood).
A diet rich in fruits, vegetables, whole grains, nuts or legumes, and ALA-rich foods may reduce the risk of heart attack and stroke, both as first-time events and after the first heart attack or stroke. One of the best ways to help prevent and treat heart disease is to eat a low-fat diet, avoiding foods rich in saturated and trans-fats and eating those 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 diets rich in omega-3 fatty acids (including ALA) may lower blood pressure in people with hypertension.
One small study compared flaxseed to hormone replacement therapy (HRT) in menopausal women and reported that 40 g of flaxseed worked as well as HRT for mild menopausal symptoms (hot flashes, mood disturbances, 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.
Lignans from flaxseed
In addition to the important omega-3 fatty acid ALA, flaxseed -- not the oil -- also contains a group of chemicals called lignans that may help protect the body from cancer. Lignans are phytoestrogens -- plant compounds that act like the hormone estrogen.
Because of the estrogen-like activity of lignans in flaxseed, scientists aren’t sure whether flaxseed would be harmful or helpful for breast cancer. Laboratory studies have reported reduction in breast tumor growth and metastasis (spreading) in rats. There has been only one clinical study in humans, in which postmenopausal women who were newly diagnosed with breast cancer ate a muffin with flaxseed 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, but much more research is needed.
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.
Results from studies are confusing when it comes to prostate cancer and flaxseed. A few studies have 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.
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, addiction, eating disorders, preterm labor, emphysema, psoriasis, glaucoma, Lyme disease, lupus, and panic attacks.
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