Here's a basic summary of many of the studies I've seen.
A common myth about the benefits of flaxseed oil...
As more and more people become aware of the importance of fat in their diet, there's growing interest in the benefits of flaxseed oil. Flaxseed oil is rich in a type of fat known as omega-3 (you'll also see it written as n-3).
Over the past few years, a number of studies have shown that fish oil (which is also high in omega-3 fatty acids) can reduce the risk of heart disease, lower your blood pressure, and also alleviate some of the symptoms of depression.
Because flaxseed oil also contains omega-3 fatty acids, it's easy to confuse the benefits of flaxseed oil with those of fish oil. However, what many don't realize is that the omega-3 fatty acids found in flax are not the same as those in fish.
Flaxseed oil
Fish oil contains two omega-3 fatty acids known as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Flaxseed oil, on the other hand, is rich in alpha-linolenic acid, which is the "parent" fatty acid to DHA and EPA.
Although similar in structure, the benefits of alpha-linolenic acid, EPA, and DHA are not the same.
Your body converts alpha-linolenic acid rapidly into EPA, and more slowly into DHA. Roughly 11 grams of alpha-linolenic acid is needed to produce one gram of DHA and EPA. However, other foods in your diet can easily put the brakes on this conversion process.
A diet that's rich in trans-fatty fatty acids, for instance, will "interfere" with the conversion of alpha-linolenic acid into EPA and DHA. Trans-fatty acids are found in foods such as cookies, some types of margarine, chips, cakes, and popcorn.
When you see hydrogenated oil on the ingredients label of a food, there are probably some trans-fatty acids in there somewhere.
Balance
It's also very important to make sure that your diet contains the right balance of omega-3 and omega-6 fatty acids.
A healthy diet consists of roughly two to four times more omega-6 fatty acids than omega-3 fatty acids. In other words, for every four grams of omega-6 fatty acids, aim for at least one gram of omega-3 fatty acids.
Because traditional sources of fat (such as butter) have been replaced with vegetable oils (sunflower oil and corn oil, for example), the typical diet contains 14 to 25 times more omega-6 fatty acids than omega-3 fatty acids.
A diet that contains too many omega-6 fatty acids at the expense of omega-3 fatty acids also limits the conversion of alpha-linolenic acid into EPA and DHA.
This doesn't mean there are no benefits of flaxseed oil. Foods high in alpha-linolenic acid (such as walnuts and flaxseed oil) are a useful addition to the diet of anyone who wants a leaner, healthier body.
They should, however, be consumed as part of a diet containing high-fat, cold-water fish (such as salmon) and/or fish oil supplements.
Reference
Gerster, H. (1998). Can adults adequately convert alpha-linolenic acid (18:3n-3) to eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)? International Journal for Vitamin and Nutrition Research, 68, 159-173
