DOES IT WORK?Flaxseed and cardiovascular health
FLAXSEED COMES from flax, a plant with a very long history in the linen industry. The seeds have also been used for nutritional and medicinal purposes.
Flaxseeds themselves are edible, containing both fibre and an oil. The fibre is made up of both insoluble components and a water soluble mucilage, and has been used as a poultice for burns and other skin irritations.
Flaxseed oil is produced by separating the fibre and other components. Traditionally, this has been called linseed oil and used in paints and varnishes. Its strong odour and flavour make it unpalatable for many, but it is edible.
Its use as a dietary supplement has led to renewed interest because of its omega-3 fatty acids. More than half of the oil is alpha-linolenic acid (ALA), making flaxseed oil one of the richest sources of this particular omega-3.
Much of the interest in omega-3s has focused on two other types, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). EPA and DHA are the main omega fats found in fish oils. Although our bodies can convert ALA into EPA or DHA, this does not happen very efficiently.
So, while flaxseed oil and fish oils contain omega-3 fatty acids, they differ in their effect in the body. Products containing ground flaxseed will have the omega-3 fatty acids along with the fibre and other active ingredients called lignans. These plant sterols are known to affect cholesterol metabolism.
Flaxseed has been used for a variety of medicinal purposes. The insoluble fibre is recommended for constipation and other gastrointestinal complaints. The soluble fibre and oil are receiving much interest for their ability to modify blood cholesterol and sugar levels and thereby provide some protection against heart disease.
Some reports have also suggested that flaxseed may help reduce the risk of certain cancers, although these studies are at a preliminary stage.
Laboratory studies have shown that ground flaxseed, flaxseed oil and flaxseed lignans can impact blood cholesterol levels. Cholesterol levels can be measured as total cholesterol, LDL-cholesterol (the “bad” cholesterol) and HDL-cholesterol (the “good” cholesterol).
Roughly speaking, a person’s risk of heart disease can be reduced by lowering the level of total cholesterol or LDL-cholesterol, or by raising the level of HDL-cholesterol.
Studies with humans have shown that people taking whole or ground flaxseed (15-50g per day) reduced their total cholesterol and LDL-cholesterol levels. However, the reductions varied between 2 and 18 per cent. The most recent studies found little reduction in people with high cholesterol levels.
The HDL-cholesterol levels remained unchanged in most studies. When flaxseed oil was examined, the results were less encouraging, with most studies finding no affect on cholesterol. A small number of other studies found that flaxseed oil did not appear to act as an antioxidant or have a blood-thinning effect.
Two small studies found that when people added flaxseed to their diet via breads and muffins, their blood glucose levels were lower.
This beneficial effect may have occurred by the
flaxseed fibre delaying absorption of glucose from the intestines.
Unripe and uncooked flaxseed contains potentially toxic cyanogenic compounds. Therefore, only processed flaxseed should be consumed.
While the lignans found in flaxseed may have beneficial effects, their chemical similarity with female sex hormones has raised concerns about consuming them in large quantities.
However, to date, no serious adverse effects have been reported with flaxseed.
Ground flaxseed, either as a supplement or used in baking, can produce a modest reduction in cholesterol levels. This, as part of a healthy diet and accompanied by exercise, may help to reduce a person’s risk of heart disease.
Flaxseed oil is unlikely to have this particular benefit, but is an excellent source of omega-3 fatty acids.
The oil can thus contribute to general health. On their own, ground flaxseed or flaxseed oil are unlikely to lead to dramatic changes, but can contribute generally to a more healthy diet.
Dónal OMathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University. He authored Alternative Medicine: The Christian Handbook, Updated and Expanded Edition, Zondervan, 2007