First of all, it's important to think about flaxseed oil as falling outside of the category of "cooking oils." It's never a good idea to treat flaxseed oil as a cooking oil—it's composition is simply too delicate and easily oxidized to risk exposure to cooking heats. But flaxseed oil can still make a valuable contribution to your nutrient intake if you think about it as plant-based oil that is rich in omega-3s and can be added to food after cooking.
Manufacturers typically produce three basic types of flaxseed oil: (1) pure oil that have been pressed out of the seeds and that contains no flaxseed particulates like lignans; (2) pure oil that has been enriched with low-to-moderate amounts of particulates; and (3) pure oil that has been enriched with moderate-to-high amounts of particulates—often marketed as "high-lignan" flaxseed oil.
We like the idea of flaxseed oil that contains particulates like lignans. It's always best to consume a food in a form that is as close as possible to its natural, whole food form. Flaxseeds aren't a whole food, since that would require a whole flax plant. But they are closer to a whole food than flaxseed oil, and the particulate contents of flaxseeds—including lignans—are known to provide important health benefits. Some of the lignans found in whole flaxseeds—for example, secoisolariciresinol, matairecinol, and pinoresinol—can be converted by intestinal bacteria into enterolactone (ENL) and enterodiol (END). Both ENL and END can directly affect our hormonal balance and may play a role in prevention of hormone-related cancer. Including lignans along with your flaxseed oil makes sense.
What is less clear to us is the best way for you to include lignans along with your flaxseed oil. As much as we like the idea of cold-pressed flaxseed oil that has been enriched with particulates from ground flaxseed (including lignans), there is no industry-wide standard for determining how much ground flaxseed to add back into a purified flaxseed oil. Minimally enriched flaxseed oils will typically (but not always) contain about 5-10 milligrams of lignans per tablespoon; moderately enriched oils will usually contain between 10-20 milligrams; and strongly enriched oils will typically contain between 20-40 milligrams. The words "high-lignan" on the labeling information cannot provide you with enough information, however, since there is no industry-wide standard for "high-lignan." So you will need to consult the nutrient information on the back of the bottle to find out how much ground flaxseed particulate has been added back to the oil. Instead of measuring all particulates—or even all lignans—that have been added back into the oil, manufacturers usually just measure the primary lignan called "secoisolariciresinol diglyceride" (which is usually abbreviated "SDG"). So you are likely to see "Lignans (SDG)" on the labeling information for a bottle of enriched flaxseed oil, and you can use this information to determine how much flaxseed particulate (including lignans) has been added back into your flax oil.
Because manufacturers often charge a much higher price for lignan-enriched oils, however, you may want to purchase a less-expensive, lignan-free (non-enriched) oil and just add ground flaxseed to your meal plan separately from the oil. Another reason that some individuals may prefer to consume ground flaxseeds separately from flax oil involves taste. Flax oil has a different taste when enriched with flax particulates, and while some people enjoy this taste and describe it as "nuttier" and more flavorful, others prefer the taste of flax oil without particulates.
You'll often hear two different types of safety concerns being raised about flaxseed oil. The first type of concern involves its easily oxidized content and susceptibility to damage by heat and light. This concern is a valid one. But fortunately, you can greatly reduce this safety concern by being very selective about the quality of flaxseed oil you purchase, as well as your handling and use of the oil. By purchasing cold-pressed flaxseed oil, you can usually obtain a high-quality oil that has been extracted from the flaxseeds at temperatures no greater than 120F (49C). The flax oil you buy should be packaged in an opaque bottle for protection from light. If it's a "shelf stable" flax oil that has been protected through the addition of natural antioxidants like vitamin E, refrigeration of the bottle during shipping may not have been required, and you may not need to refrigerate the oil until the bottle has been first opened. If not preserved with natural antioxidants, however, flax oil should be refrigerated throughout the shipping process and during home storage, even prior to opening. Once opened, all bottles of flax oil should be refrigerated for safety.
A second safety concern that's been raised about flax oil involves its ALA (alpha-linolenic acid) content. It's common for a tablespoon of flax oil to contain 7 grams of ALA—over half of its total fat content. ALA is widely documented as a heart-healthy, omega-3 fat. However, beginning in the late 1990's some case-control research studies raised questions about the relationship between high intake of ALA and risk of prostate cancer. It's important to note that none of these studies were specific to flax oil, but simply to total ALA intake from all foods in the diet. We've reviewed that early research, as well as recent studies on ALA and prostate cancer, and we cannot find consistent evidence of a safety risk in this regard. Here are the most important pieces of information that we think you should know from these studies:
Taken as a whole, we believe that existing research shows no convincing evidence that risk of prostate cancer is increased by intake of ALA, and that intake of ALA may actually help protect against risk of prostate cancer by helping avoid a high ratio of omega-6/omega-3 fat.
There is little question in our mind about the greater health benefits of whole ground flaxseeds versus flax oil. Even if particulates from ground flaxseed have been added back into purified flax oil, the health benefits are greater from the seeds themselves which contain all of the particulates and not simply some percentage.
It's important to recognize major areas in which whole flaxseeds are nutritionally different from purified flax oil. The first area involves fiber and fiber-related components like lignans. One tablespoon of whole flaxseeds contains nearly 2 grams of fiber, and 40-45 milligrams of lignans, whereas one tablespoon of purified (unenriched) flax oil contains 0 grams of fiber and 0 milligrams of lignans. A second area involves protein. One tablespoon of whole flaxseeds typically contains about 1.3 grams of protein, compared to 0 grams in purified (unenriched) flax oil. The protein component of whole flaxseeds includes essential branched-chain amino acids like leucine, isoleucine, and valine as well as essential sulfur-containing amino acids like cysteine and methionine. Finally, whole flaxseeds are a very good source of minerals like manganese and vitamins like vitamin B1, and a good source of minerals like magnesium. These minerals and vitamins are virtually absent from pure (unenriched) flax oil.
If you decide to purchase enriched flaxseed oil, you will typically be getting an oil that contains between 5-40 milligrams of lignans. When the term "high-lignan" appears on a label, you may be getting lignan content at the higher end of this range, even though there is no industry-wide standard for "high-lignan." Some enriched flaxseed oils may actually end up containing the same approximate amount of lignans found in whole flaxseeds. However, there is no way for you to determine this information unless is it presented on the Supplement Facts Panel. And unfortunately, the Supplement Facts Panel—even when available—often fails to provide an exact lignan amount, but states total lignan content within a general range, for example, 5-25 milligrams. (Still, if 25 milligrams is the highest possible amount in the range, at least you know that you're getting a little more than half the total lignan amount found in whole flaxseeds.)
In terms of fiber, you may get anywhere from 0-2 grams of fiber in enriched flaxseed oils, compared with 3 grams in the same amount of whole flaxseeds. In terms of protein, we have not seen any commonly available enriched flaxseed oils that contained enough protein to register higher than 0 grams per tablespoon on the Supplement Facts Panel, even though very small amounts of protein are likely to be contained in the oil. These nutritional differences between whole flaxseeds and pure (unenriched) flax oil can be important from a health standpoint. For example, secoisolariciresinol, matairecinol, and pinoresinol—three of the lignans found in whole flaxseed—can be converted by intestinal bacteria into enterolactone (ENL) and enterodiol (END). Both ENL and END can directly affect our hormonal balance and may play a role in prevention of hormone-related cancer.
For the above reasons, we view whole flaxseeds and whole ground flaxseeds as providing intrinsically greater health benefits that flaxseed oil. However, we also recognize that some of the health benefits provided by whole flaxseeds can be restored to high-quality flaxseed oils through enrichment with ground flaxseed.
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Williams CD, Whitley BM, Hoyo C et al. A high ratio of dietary n-6/n-3 polyunsaturated fatty acids is associated with increased risk of prostate cancer. Nutrition Research, Volume 31, Issue 1, January 2011, Pages 1-8.
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