Taking flaxseed oil supplements has some real benefits.
While fish oil contains the docosahexaenoic acid (DHA) and eicosahexaenoic acid (EPA) that flaxseed oil that flaxseed oil does not, flaxseed oil does contain an omega-3 essential fatty acid called alpha-linolenic acid (ALA) that the body can use to make DHA and EPA. If you consume flaxseed oil as your omega-3 source, there's no way you will overdose on omega-3's.
On the other hand, overdosing on omega-3 essential fatty acids is a very rare occurrence. While we all need to consume omega-3 essential fatty acids and omega-6 essential fatty acids in balance, most of us consume 20 to 60 times more omega-6 than omega-3. Getting too many omega-3's is not usually the problem!
Even if you take fish oil, you body also needs some ALA to make other kinds of fatty acids used to make anti-inflammatory hormones. You can get ALA from flaxseed oil, hempseed oil, almonds, or walnuts, and you just need a little to keep your fatty acids in balance. Two or three servings a week is enough. But you need DHA and EPA every day.
Highly processed flaxseed oil is potentially toxic.
Internationally renowned expert on essential fatty acids Udo Erasmus tells us that deodorized, decolorized flaxseed oil is potentially toxic. The nickel catalysts used to make the oil more attractive in consumer packaging damage 0.5 to 1.0 per cent of the ALA molecules within into a form that actually accelerates free radical damage of cholesterol and encourages hardening of the arteries.
If you choose to supplement with flaxseed oil, use a cold-pressed oil that is extracted with a mechanical process. You don't want to use one of the many brands of flaxseed oil that are extracted by treating them with hexane and then boiling off the toxic solvent.
Flaxseed oil competes with other essential nutrients.
The human body needs the omega-3 essential fatty acid in flaxseed oil, alpha-linolenic acid, to make anti-inflammatory hormones. It also needs the omega-6 essential fatty acid alpha-linoleic acid to make pro-inflammatory hormones that activate the immune system, kill cancer cells, and stop bleeding. Alpha-linolenic acid and alpha-linoleic acid compete for enzymes needed to change them into needed hormones and regulatory substances. If you take too much flaxseed oil, you can weaken your immune system.
Flaxseed oil provides the raw materials for DHA and EPA, but you have to consume a lot of calories to get the DHA and EPA you need.
The human body can get DHA and EPA from fish oil directly, consuming no more than 30 to 40 calories a day in the process. The human body can make DHA and EPA from the ALA in flaxseed oil, but only 1 to 10 per cent of the fatty acids in flaxseed oil actually are transformed into DHA and EPA. The rest are burned in your body, or stored in your fat. You can consume 30 or 40 calories of fish oil or 300 to 400 calories of flaxseed oil for the same effect.
Flaxseed oil can have an unexpected effect if you have congestive heart failure.
Both flaxseed oil and fish oil contain omega-3 essential fatty acids that "switch off" hyperactive cells in the heart. This lowers the risk of sudden death caused by an "electrical storm" in the heart that leads to cardiac arrest, but it can stress the heart if you have congestive heart failure. No one has ever died from congestive heart failure as a direct result of taking flaxseed oil, but since you need 10 times as much flaxseed oil as fish oil to get your omega-3's, additional stress on the heart is possible if you have this condition.
Flaxseed oil is fine as an occasional addition to your diet. Walnuts, cooked soybeans (edamame), soybean oil, canola oil, and hempseed oil are helpful, too. But for day to day supplementation to get your omega-3's, products like Omega-3 DHA, Omega-3 Premium, or Omega-3 QH/Ultra are best.