Its proponents claim that flaxseed can help reduce the risk of diabetes, heart disease, stroke and some cancers. Fact or Fancy? And is flaxseed suitable for type 2 diabetics?
Flaxseed has been cultivated for at least 5,000 years and has long been reputed to deliver a variety of health benefits.
Its healthful reputation continues to grow and nowadays flaxseed is an ingredient in all types of food products, from waffles to crackers.
The seed is also being used as chicken-feed in order to increase the levels of plant omega-3 fatty acids in eggs.
What’s in flaxseed
Flaxseed (also called linseed) is a great source of some of the B vitamins, such as thiamine, B6, niacin and folate.
It is also an excellent source of many dietary minerals, including manganese, magnesium, phosphorus, selenium, iron, zinc, calcium and potassium.
It is very low in cholesterol and sodium.
Flaxseed is high in protein and low in sugar.
However it is high in fat (a bit over 40% by weight) and two-thirds of the calories it delivers are from fat.
This makes eating it in large quantities inadvisable for type 2 diabetics, as one of the essential steps you need to take in order to beat your diabetes is to eliminate fat from your diet as far as possible.
Despite its high fat content, flaxseed has a healthful reputation. This reputation is based on three of its components: dietary fibre, lignans and essential fatty acids.
Dietary fibre … 100 grams of flaxseed contains 27g of soluble and insoluble fibre. It also contains mucilage, a gummy material.
Both the fibre and the mucilage expand in water, which adds bulk to the stool and has a laxative effect.
Lignans … are phytoestrogens, plant chemicals, which have both plant oestrogen and antioxidant properties. Lignans may help protect against certain cancers.
Flaxseed contains from 75 times to 800 times more lignans than other plants.
Alpha-linolenic acid (ALA) … is an omega-3 fatty acid that may be helpful for heart disease and other health problems. ALA is also found in other plants, while other omega-3 fatty acids are found in fish.
Flaxseed contains plenty of ALA; indeed one tablespoon of ground flaxseed contains about 1.8g of plant omega-3.
With these three super-ingredients packed in a tiny seed, the many claims for the health benefits of flaxseed are not surprising.
Flaxseed contains an oil which is often called linseed oil.
This oil only contains the ALA from the seed (about 7g per 15mL, ie a tablespoon’s worth) and not the lignans or fibre.
Health benefits of flaxseed
The claimed health benefits of flaxseed range from the prevention of cancer and cardiovascular disease to help in controlling the blood glucose levels of type 2 diabetics.
Most of these claims, however, need to be confirmed by properly conducted clinical trials with human subjects.
Two of the components in flaxseed, ALA and the lignans, may help protect against breast, prostate and colon cancers.
In animal studies, ALA has been found to inhibit the incidence and growth of tumours.
Lignans can block the enzymes involved in hormone metabolism and so interfere with the growth and spread of tumour cells. Lignans also have antioxidant properties.
Despite all the hype, the effectiveness of flaxseed in combating various cancers has not been proved adequately and clinical trials using human subjects are needed.
Breast cancer … in laboratory studies, flaxseed has reduced the growth of breast tumours and metastasis (spreading of cancer) in rats.
One clinical study in humans found that adding flaxseed to the diet of postmenopausal women who had been recently diagnosed with breast cancer may have the potential to reduce the growth of tumours. One study, however, does not a certainly make.
Colon cancer … animal studies show that lignans may slow the growth of tumours in the colon. Clinical trials in people are needed.
Prostate cancer … here the studies are contradictory.
A few studies appear to show that ALA is associated with an increased risk of this cancer, while other studies suggest that men at risk of prostate cancer may benefit from eating flaxseed.
Only proper, extensive clinical trials in humans can clear up the confusion.
Both flaxseed and linseed oil have been reported to lower cholesterol levels. But, as for prostate cancer, the studies in humans have been confusing.
One study did find that persons who added flaxseed to diets that were already low in cholesterol improved their cholesterol ratio, ie they lowered the proportion of their LDL (bad) cholesterol as a proportion of their total cholesterol. They also reduced their triglycerides.
The cholesterol-lowering effect of flaxseed is though to be due to the combined benefits of the seed’s ALA, fibre, and lignans.
The effect of adding flaxseed to the diet of persons who already have elevated cholesterol levels does not appear to have been researched.
Several illnesses, including asthma and Parkinson’s disease, are accompanied by inflammation.
It may be that flaxseed can help block the release of the inflammatory agents involved, as ALA has been shown to decrease inflammatory reactions in humans, while studies in animals have found that lignans can decrease the levels of several pro-inflammatory agents.
Again, clinical trials using human subjects are required.
Research suggests that plant omega-3s help the cardiovascular system in various ways, such as anti-inflammatory action and normalizing the heartbeat.
New research also suggests that diets rich in omega-3 fatty acids (including ALA) may lower blood pressure in people with hypertension.
Several studies suggest that diets rich in flaxseed omega-3s help prevent hardening of the arteries and keep plaque from being deposited in the arteries partly by preventing white blood cells from sticking to the inner lining of blood vessels. The lignans found in flaxseed have been shown to reduce atherosclerotic plaque build-up by up to 75%.
ALA in food may reduce the risk of heart attack and stroke, both for persons who have already had a heart attack or stroke and for persons who have not experienced either of these events.
Evidence suggests that people who eat a diet rich in ALA are less likely to have a fatal heart attack. This may be because flaxseed helps prevent heart attacks and strokes by reducing the inflammation associated with plaque build-up in the arteries.
My use of the verb ‘suggests’ or the qualifier ‘may’ to describe the effect of flaxseed on the cardiovascular system indicates that nothing has been proved with any degree of certainty.
A single study found that 40g of flaxseed worked just as well as hormone replacement therapy in reducing menopausal symptoms, such as hot flashes, vaginal dryness and mood disturbances, in women who were becoming infertile.
However, a larger follow-up study found that flaxseed did not improve menopausal symptoms.
In fact, other studies that have shown that there is no significant difference between flaxseed and a placebo in the effect they have on these symptoms.
Little or no research has been undertaken on the effect flaxseed in the diet has on the blood glucose levels of type 2 diabetics. However researchers in the WHO (World Health Organisation) recently published an open-label study on the use of flaxseed powder to control diabetes.
An open-label trial is a clinical trial in which both the researchers and participants know what is being done. It is used during the early stages of the testing of drugs, devices and methodologies.
An open-label trial is usually carried out with a small number of participants, and acts as an initial study of safety and effectiveness.
In the WHO trial, diabetics took a tablespoon of ground flaxseeds every day for a month. They experienced a significant drop in their levels of fasting blood glucose, triglycerides, cholesterol and Haemoglobin A1c compared to the control group.
It seems, however, that if type 2 diabetics already have their blood glucose under control, the flaxseed will have no effect.
This was a smalls study and possibly the results were a fluke. However the seed’s components … dietary fibre, lignans and ALA, as well as vitamins and minerals … suggest that flaxseeds do have plenty of other benefits.
Most of these benefits however still need to be clinically proven.
Though the seeds contain over 40% fat by weight, the amount of fat in a tablespoon (7g) will be only about 3g or 5% of the recommended daily intake of fat for a healthy adult, so a single spoon of flaxseed a day should not adversely affect someone who is controlling their diabetes with a low-fat diet.