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Also indexed as: Lignan, Linseed Oil, Linum usitatissimum
What does it do? Like most vegetable oils, flaxseed oil contains linoleic acid, an essential fatty acid needed for survival. But unlike most oils, it also contains significant amounts of another essential fatty acid, alpha linolenic acid (ALA).
ALA is an omega-3 fatty acid. To a limited extent, the body turns ALA into eicosapentaenoic acid (EPA)—an omega-3 fatty acid found in fish oil—which in turn converts to beneficial prostaglandins. (Prostaglandins are hormone-like substances made in many parts of the body rather than coming from one organ, as most hormones do.) While fish oil has been shown to have anti-inflammatory activity, an anti-inflammatory effect of flaxseed oil has not been demonstrated conclusively.
Some doctors have argued that, because ALA can be converted to EPA and DHA (the fatty acids found in fish oil), flaxseed oil should be useful for the same conditions as fish oil. However, the conversion of ALA to EPA and DHA is limited, so that argument may turn out to be incorrect. For example, while numerous studies have shown that fish oils are beneficial for rheumatoid arthritis, flaxseed oil failed to work for this condition in the only known trial.1 In 1994, a diet purportedly high in ALA was successful in preventing heart disease,2 but this study altered many dietary factors, so ALA may not have been solely responsible for the outcome.3 Flaxseed oil does not appear to be a good replacement for fish oil for people with elevated triglycerides.4 5 ALA does not reduce excess platelet aggregation ("sticky platelets"), another risk factor for heart disease, the way fish oil does.6 However, flaxseed oil may help lower cholesterol,7 and research specific to flaxseed oil indicates that it may also lower blood pressure.8
Where is it found? In addition to its presence in flaxseed oil, small amounts of ALA are also found in canola, soy, black currant, and walnut oils.
Who is likely to be deficient? ALA deficiencies are possible but believed to be rare, except in infants who are fed formula that is omega-3 deficient.
How much is usually taken? Although it is not suitable for cooking, flaxseed oil (unlike fish oil) can be used in salads. Some doctors recommend that people use 1 tablespoon (15 ml) of flaxseed oil per day as a supplement in salads or on vegetables to ensure a supply of essential fatty acids. Some conversion of ALA to EPA does occur,9 and this conversion can be increased by restricting the intake of other vegetable oils.10
For those who wish to replace fish oil with flaxseed oil, research suggests taking up to ten times as much ALA as EPA.11 Typically, this means 7.2 grams of flaxseed oil equals 1 gram of fish oil. However, even if taken in such high amounts, flaxseed oil may not have the same effects as fish oil. But, flaxseed oil will not cause a fishy-smelling burp (a possible side effect of fish oil).
Are there any side effects or interactions? Flaxseed oil toxicity has not been reported. However, there is conflicting information about the effect of flaxseed oil and one of its major constituents, ALA, on cancer risk.
While most test tube and animal studies suggest a possible protective role for ALA against breast cancer,12 13 14 15 16 one animal study17 and a preliminary human study18 suggested increased breast cancer risk from high dietary ALA. Another preliminary human study reported that higher breast tissue levels of ALA are associated with less advanced breast cancer at the time of diagnosis.19 For prostate cancer, a test tube study reported ALA promoted cancer cell growth,20 but preliminary human studies have shown ALA to be associated with either an increased21 22 or decreased risk,23 or no change24 at all.
Advocates of flaxseed oil speculate that a potential association between ALA and cancer may be due to the fact that meat contains ALA, thus implicating ALA when the real culprits are probably other components of meat. In some studies, however, saturated fat (and therefore probably meat) were taken into consideration, and ALA still correlated with increased risk. The associations between ALA and cancer might eventually be shown to be caused by substances found in foods rich in ALA rather than by ALA itself. However, ALA has been reported to become mutagenic (able to cause precancerous changes) when heated,25 which concerns some doctors.
The effect of ALA as an isolated substance, and of flaxseed oil on the risk of cancer in humans remains unclear, with most animal and test tube studies suggesting protection, and some preliminary human trials suggesting cause for concern. It is premature to suggest that ALA and flaxseed oil will either cause or protect against human cancer at this time.
Flaxseed oil is not suitable for cooking and should be stored in an opaque, airtight container in the refrigerator or freezer. If the oil has a noticeable odor it is probably rancid and should be discarded.
What does it do? Like most vegetable oils, flaxseed oil contains linoleic acid, an essential fatty acid needed for survival. But unlike most oils, it also contains significant amounts of another essential fatty acid, alpha linolenic acid (ALA).
ALA is an omega-3 fatty acid. To a limited extent, the body turns ALA into eicosapentaenoic acid (EPA)—an omega-3 fatty acid found in fish oil—which in turn converts to beneficial prostaglandins. (Prostaglandins are hormone-like substances made in many parts of the body rather than coming from one organ, as most hormones do.) While fish oil has been shown to have anti-inflammatory activity, an anti-inflammatory effect of flaxseed oil has not been demonstrated conclusively.
Some doctors have argued that, because ALA can be converted to EPA and DHA (the fatty acids found in fish oil), flaxseed oil should be useful for the same conditions as fish oil. However, the conversion of ALA to EPA and DHA is limited, so that argument may turn out to be incorrect. For example, while numerous studies have shown that fish oils are beneficial for rheumatoid arthritis, flaxseed oil failed to work for this condition in the only known trial.1 In 1994, a diet purportedly high in ALA was successful in preventing heart disease,2 but this study altered many dietary factors, so ALA may not have been solely responsible for the outcome.3 Flaxseed oil does not appear to be a good replacement for fish oil for people with elevated triglycerides.4 5 ALA does not reduce excess platelet aggregation ("sticky platelets"), another risk factor for heart disease, the way fish oil does.6 However, flaxseed oil may help lower cholesterol,7 and research specific to flaxseed oil indicates that it may also lower blood pressure.8
Where is it found? In addition to its presence in flaxseed oil, small amounts of ALA are also found in canola, soy, black currant, and walnut oils.
Who is likely to be deficient? ALA deficiencies are possible but believed to be rare, except in infants who are fed formula that is omega-3 deficient.
How much is usually taken? Although it is not suitable for cooking, flaxseed oil (unlike fish oil) can be used in salads. Some doctors recommend that people use 1 tablespoon (15 ml) of flaxseed oil per day as a supplement in salads or on vegetables to ensure a supply of essential fatty acids. Some conversion of ALA to EPA does occur,9 and this conversion can be increased by restricting the intake of other vegetable oils.10
For those who wish to replace fish oil with flaxseed oil, research suggests taking up to ten times as much ALA as EPA.11 Typically, this means 7.2 grams of flaxseed oil equals 1 gram of fish oil. However, even if taken in such high amounts, flaxseed oil may not have the same effects as fish oil. But, flaxseed oil will not cause a fishy-smelling burp (a possible side effect of fish oil).
Are there any side effects or interactions? Flaxseed oil toxicity has not been reported. However, there is conflicting information about the effect of flaxseed oil and one of its major constituents, ALA, on cancer risk.
While most test tube and animal studies suggest a possible protective role for ALA against breast cancer,12 13 14 15 16 one animal study17 and a preliminary human study18 suggested increased breast cancer risk from high dietary ALA. Another preliminary human study reported that higher breast tissue levels of ALA are associated with less advanced breast cancer at the time of diagnosis.19 For prostate cancer, a test tube study reported ALA promoted cancer cell growth,20 but preliminary human studies have shown ALA to be associated with either an increased21 22 or decreased risk,23 or no change24 at all.
Advocates of flaxseed oil speculate that a potential association between ALA and cancer may be due to the fact that meat contains ALA, thus implicating ALA when the real culprits are probably other components of meat. In some studies, however, saturated fat (and therefore probably meat) were taken into consideration, and ALA still correlated with increased risk. The associations between ALA and cancer might eventually be shown to be caused by substances found in foods rich in ALA rather than by ALA itself. However, ALA has been reported to become mutagenic (able to cause precancerous changes) when heated,25 which concerns some doctors.
The effect of ALA as an isolated substance, and of flaxseed oil on the risk of cancer in humans remains unclear, with most animal and test tube studies suggesting protection, and some preliminary human trials suggesting cause for concern. It is premature to suggest that ALA and flaxseed oil will either cause or protect against human cancer at this time.
Flaxseed oil is not suitable for cooking and should be stored in an opaque, airtight container in the refrigerator or freezer. If the oil has a noticeable odor it is probably rancid and should be discarded.