Based upon research and public health recommendations, we believe that a combination of nuts and seeds (including flaxseeds), that adds up to 3 tablespoons (1.5 ounces, or 42 grams) per day is a dietary step well worth taking for most people. For more background on this recommendation, please see this article.
The seeds of most plants are rich in nutrients and can provide us with health benefits. Yet flaxseeds are also nutritionally unique and offer us health benefits not found across the board within the seeds food group. The nutritional uniqueness of flaxseeds features three nutrient aspects, and all three play a key role in the outstanding health benefits of this food.
The first unique feature of flax is its high omega-3 fatty acid content. Among all 127 World's Healthiest Foods, flaxseeds comes out number one as a source of omega-3s! The primary omega-3 fatty acid found in flaxseeds is alpha-linolenic acid, or ALA. The ALA in flaxseed has found to be stable for at least 3 hours of cooking at oven temperatures (approximately 300F/150C), which makes it available after ground flaxseeds have been added to baked goods like muffins or breads.
The second unique feature of flaxseed is its lignans. Lignans are fiber-like compounds, but in addition to their fiber-like benefits, they also provide antioxidant protection due to their structure as polyphenols. The unique structure of lignans gives them a further health-supportive role to play, however, in the form of phytoestrogens. Along with isoflavones, lignans are one of the few naturally occurring compounds in food that function as weak or moderate estrogens when consumed by humans. Among all foods commonly eaten by humans, researchers rank flaxseeds as the number one source of lignans. Sesame seeds come in second, but contain only one-seventh of the total lignans as flaxseeds. To give a few further examples, sunflower seeds contain about 1/350th as many lignans, and cashews nuts contain about 1/475th as many lignans as flaxseeds.
A third unique feature of flaxseeds is their mucilage (gum) content. "Mucilage" refers to water-soluble, gel-forming fiber that can provide special support to the intestinal tract. For example, gums can help prevent the too rapid emptying of the stomach contents into the small intestine, thereby improving absorption of certain nutrients in the small intestine. Arabinoxylans and galactoxylans are included within the mucilage gums found in flaxseeds.
This combination of features—omega-3 fatty acids, high-lignan content, and mucilage gums—is a key factor in the unique health benefits of flaxseeds. The specific areas of health benefit described below all draw in some way from this unique combination of nutrients not found in other commonly eaten nuts or seeds.
The primary omega-3 fatty acid in flaxseeds—alpha-linolenic acid, or ALA—can be helpful to the cardiovascular system in and of itself. As the building block for other messaging molecules that help prevent excessive inflammation, ALA can help protect the blood vessels from inflammatory damage. Numerous studies have shown the ability of dietary flaxseeds to increase our blood levels of ALA, even when those flaxseeds have been ground and incorporated into baked goods like breads or muffins. When flaxseeds are consumed, two other omega-3 fatty acids have also been shown to increase in the bloodstream, namely, eicosapentaenoic acid (EPA) and docosapentaenoic acid (DPA). Increases in EPA and DPA also help provide inflammatory protection.
Protection of our blood vessels from inflammatory damage is also provided by the lignans in flaxseeds. These lignans can inhibit formation of platelet activating factor (PAF), which increases risk of inflammation when produced in excessive amounts. The overall anti-inflammatory benefits of ALA and lignans in flaxseeds has been further corroborated by studies in which flaxseed-enriched baked goods (like muffins) lead to decreases of 10-15% in C-reactive protein (CRP) levels. CRP levels are a commonly used indicator of inflammatory status in the cardiovascular system.
Risk of oxidative stress in the blood vessels can also be lowered by flaxseed intake. In addition to being a very good source of the mineral antioxidant manganese, polyphenols in flaxseed—including flaxseed lignans—provide measurable antioxidant benefits. The antioxidant benefits of one particular flaxseed lignan, secoisolariciresinol, have been especially well-documented. Decreased lipid peroxidation and decreased presence of reactive oxygen species (ROS) in the bloodsteam have both been associated with flaxseed intake in amounts of approximately 2 tablespoons per day.
Intake of flaxseeds has also been shown to decrease the ratio of LDL-to-HDL cholesterol in several human studies and to increase the level of apolipoprotein A1, which is the major protein found in HDL cholesterol (the "good" cholesterol). This HDL-related benefit may be partly due to the simple fiber content of flaxseeds, since 2 tablespoons of ground flaxseed provide about 4 grams of dietary fiber.
Although direct studies on flaxseed and blood pressure are limited (and mostly confined to flaxseed oil versus ground flaxseed), numerous studies have shown the ability of increased omega-3 fatty acid intake to help regulate blood pressure and to help reduce blood pressure in persons who have been diagnosed with hypertension. With its excellent content of the omega-3 fatty acid alpha-linolenic acid (ALA), flaxseed can definitely help us increase our overall omega-3 intake and, by doing so, decrease our risk of high blood pressure.
There is one area of concern that we want to note involving flaxseeds and the cardiovascular system. We've seen one very small-scale study from Canada involving 30 children and teens (ages 8-18), all previously diagnosed with hypercholesterolemia (high cholesterol) and given added flaxseed in their diets over a period of 4 weeks. The flaxseed amount was 2 tablespoons, and the form was ground flaxseeds incorporated into breads and muffins. In this study, blood levels of total cholesterol and LDL cholesterol did not significantly change, but blood fat levels (in the form of triglycerides) increased and HDL cholesterol (the "good" cholesterol) decreased. Since we would consider these changes in blood lipids to be unwanted, we believe this study raises some preliminary questions about the role of daily flaxseeds in amounts of 2 tablespoons or above in the diet of children and teenagers who are already known to have high cholesterol. Much more research is needed in this area, but if you are the parent of a child or teen who is already diagnosed with high cholesterol, we recommend that you consult with your healthcare provider about the pros and cons of incorporating flaxseeds into your child's meal plan on a daily basis in any substantial amount.
It is important to realize that the antioxidant and anti-inflammatory benefits of flaxseed do not apply only to the cardiovascular system. Oxidative stress (which is often related to deficient intake of antioxidant nutrients) and excessive inflammation (which can also be related to deficient intake of anti-inflammatory nutrients) are common risk factors for a wide variety of health problems. These problems include development of insulin resistance, type 2 diabetes, asthma, obesity, and metabolic syndrome. There is preliminary evidence that flaxseed intake can decrease risk of all the problems above by increasing our anti-inflammatory and antioxidant protection.
The antioxidant and anti-inflammatory benefits of flaxseeds also make them a logical candidate for cancer prevention. That's because chronic inflammation (even low level inflammation) and chronic oxidative stress are risk factors for cancer development. In the case of flaxseeds, evidence of risk reduction is strongest for breast cancer, prostate cancer, and colon cancer. Breast cancer and prostate cancer are included in the list of cancers know as "hormone-related" cancers. Their risk reduction may be more closely related to flaxseed than risk reduction for other cancers due to the high lignan content of flaxseed.
Three of the lignans found in flaxseeds—secoisolariciresinol, matairecinol, and pinoresinol—can be converted by intestinal bacteria into enterolactone (ENL) and enterodiol (END). ENL and END have direct affects on our hormonal balance and in this way may play an especially important role in hormone-related cancer. In addition to decreased risk of breast and prostate cancer following flaxseed intake, there is also some preliminary evidence that ENL and END may be able to alter the course of hormone-dependent tumors once they are formed. The relationship between flaxseed intake and cancer prevention is complicated, however, due to the important role of gut bacteria in converting secoisolariciresinol and other lignans in flax into enterolactone and enterodiol. This conversion process involves many different enzyme-related steps provided by a complicated mix of gut bacteria including Bacteriodes, Bifidobacterium, Butyribacterium, Eubacterium and others.
The lignans provided by flaxseed have also been shown to spark increased activity by certain Phase II detoxification enzymes that are responsible for deactivating toxins in the body. This support of the detox process may help prevent accumulation of toxins that might otherwise act as carcinogens and increase cancer risk.
Benefits of flaxseed for the digestive tract—although mentioned earlier throughout this food profile—are worth repeating here. The strong fiber content of flaxseeds—including their mucilaginous fiber—help to delay gastric emptying and can improve intestinal absorption of nutrients. Flaxseed fibers also help to steady the passage of food through our intestines. Finally, the lignans in flaxseed have been shown to reduce risk of colon cancer. This impressive group of digestive tract benefits is likely to receive more attention in future research studies.
We've seen mixed findings in the area of post-menopausal benefits (such as reduction of hot flashes) and flaxseed intake, with some studies showing significant benefits and other studies showing a lack of significant benefits. However, there continues to be strong interest in flaxseeds and their components (including enterolactone and secoisolariciresinol diglucoside) as potential aids during management of perimenopausal and postmenopausal symptoms as well as during hormone replacement therapy (HRT).
This area of flaxseed research is admittedly complex. For example, enterolactone made from flaxseed lignans has been shown to be an estrogen agonist (promoting estrogen production, through increased formation of transcription factors like ER-alpha and ER-beta), as well as an estrogen antagonist (working against estrogen production, through inhibition of enzymes like estrogen synthetase). It's also known to lower the activity of 5-alpha-reductase (an enzyme that converts testosterone into dihydrotestosterone) and 17-beta hydroxysteroid dehydrogenase (an enzyme that converts estrone into estradiol). Given this complicated set of circumstances that may vary from one woman to another, it may turn out that flaxseed intake is simply better at lessening menopausal symptoms in some women, and not as good at lessening symptoms in others.
Although we've already mentioned decreased risk of insulin resistance in relationship to flaxseed intake, we're definitely expected to see more research studies in this area. The strong fiber content, antioxidant content, and anti-inflammatory content of flaxseeds make them a natural here.
One final note about the health benefits of flaxseeds involves their feeding to animals. We've seen repeated studies on the content of beef, chicken, and eggs that reflect significantly increased omega-3 content in these foods when flaxseed meal and/or flaxseed oil are added to the diets of cows and chickens. For persons who enjoy these foods in their meal plan on a regular basis, this increased omega-3 content can really add up. Some manufacturers of beef, chicken, and eggs provide omega-3 information on their product packaging. Consumption of certified organic animal foods in which flaxseed was added to the animals' feed can be an effective way of increasing your omega-3 intake.
The scientific name for flax—Linum usitatissimum— reveals a lot about our human relationship to this plant. The "linum" part of this name sounds a lot like "linen," which is a fabric that has been made from flax for over 3,000 years. The "usitatissimum" part of its name means "of greatest use" in Latin, and that quality also rings true in our relationship to flax. This plant has served not only as a food source and source of linen, but also for the creation of sails on sailing ships, bowstrings, and body armor. Flaxseed is known in many parts of the world as "linseed," although most of the linseed oil sold in the United States is not food grade and is sold instead for use as a wood finish and preservative.
Brown flax and golden flax (sometimes called yellow flax) are the two basic varieties of flax, and they are similar in their nutritional composition, with one important exception. One specific strain of yellow flax called "solin" was been developed by agricultural scientists to be processed and sold as a cooking oil that could substitute for oils like sunflower seed oil. Solin has been approved by the Food and Drug Administration (FDA) as a GRAS list food, and it is sometimes being produced under the trademarked name "Linola" (TM). Since solin (Linola TM) only contains about 1/10th of the alpha-linolenic (ALA) content of other the brown and golden flax varieties, it definitely should not be considered equivalent from a nutritional standpoint.
One additional clarification about varieties of flax is also important. New Zealand flax, even though it bears the same name, is not related to the flax plant Linum usitatissimum whose flaxseeds we recommend as a World's Healthiest Food. New Zealand flax also has a rich history of use for its fiber content, however, as well as traditional medicinal uses as developed by the Maori peoples of New Zealand.
In their raw form, flaxseeds usually range from amber/yellow/gold in color to tan/brown/reddish brown. White or green flaxseeds have typically been harvested before full maturity, and black flaxseeds have typically been harvested long after full maturity. Generally speaking, we recommend avoiding raw flaxseeds that are white, green, or black in color.
Sometime between 4000 and 2000 BC, flax cultivation became a common practice in countries bordering the Mediterranean Sea and in regions of the Middle East, and there is some evidence that flax cultivation may have started even thousands of years earlier, during the Neolithic Era of approximately 10,000 BC. From the very beginning, the value of flax was both culinary and domestic, since flax fibers could be spun into linen to provide clothing and other textile-related products.
To this day, flax cultivation has remained both culinary and domestic, although crop production has become more specialized and wide scale. In the United States and Canada, most commercial flax production involves oilseed varieties of flax, in which the seeds will eventually be dried and crushed and used to produce different grades of oil. Non-food grade flaxseed/linseed oil is used in wood finishes, paints, coatings, and other industrial supplies. Food grade flaxseed/linseed oil can as be used in livestock feed, or as a culinary oil. (It is much more common, however, for livestock feed to contain flaxseed meal versus flaxseed oil.) Oilseed varieties of flax are typically classified as oilseed crops along with soybeans, rapeseed, cottonseed, sunflower seed, and peanuts. Canada is the world's largest producer of oilseed flax, followed by Russia, France, and Argentina.
Fiber flax is the other major variety of flax in terms of commercial production. In Europe, France and Belgium are especially large producers of fiber flax. While cotton, wool and silk remain the most popular natural fibers in the global textile market, the global flax market has grown in recent years following increased production of linen products in China.
Alongside of these other flax markets, however, has developed a gradually expanding consumer market for flaxseeds themselves, to be considered as uniquely nourishing food. We expect to see food interest in flaxseeds increase, primarily because of their unique nutrient combinations and health benefits.
Flaxseeds can be purchased either whole or already ground. The two different forms offer distinct benefits. Because flaxseeds can be very difficult to chew, grinding of the seeds prior to consumption can usually increase their digestibility. However, grinding takes time, and pre-ground flaxseeds can have great convenience. On the other side of the coin, pre-ground flaxseeds—while more convenient—also come with a shorter shelf life than whole flaxseeds. Ground flaxseeds—even when carefully packaged in a gas-flushed, light-protective pouch and refrigerated after opening—typically last about 6-16 weeks. Whole flaxseeds, on the other hand, will typically last for 6-12 months when stored in an airtight container in a dark, cool dry spot. If directly refrigerated, they may last for 1-2 years.
Whole flaxseeds are generally available in prepackaged containers as well as bulk bins. Just as with any other food that you may purchase in the bulk section, make sure that the bins containing the flaxseeds are covered and that the store has a good product turnover so as to ensure their maximal freshness. Whether purchasing flaxseeds in bulk or in a packaged container, make sure that there is no evidence of moisture. If you purchase whole flaxseeds, either store them in an airtight container in a dark, dry and cool place or place their airtight container directly in the refrigerator.
Ground flaxseeds are usually available both refrigerated and non-refrigerated. If you are purchasing ground flaxseed that is sitting on the store shelf at room temperature, we highly recommended that the flaxseed be packaged in a gas-flushed, vacuum-sealed bag. If you are purchasing ground flaxseed that is found in the refrigerator section, it's not essential that vacuum-sealed packaging be used, but it can still be helpful from a food quality standpoint. Regardless of the form in which you purchase your ground flaxseeds, you should keep their container in the refrigerator after opening. The reason for all of this extra precaution is simple: once flaxseeds are ground, they are much more prone to oxidation and spoilage. Similarly, if you are grinding whole flaxseeds on your own at home (for example, in a small spice or coffee grinder), you'll want to store them in the refrigerator in an airtight container. If using glass, you may also want to use a darkened glass as that will lessen exposure of the ground flaxseeds to light.
Flaxseed oil is especially perishable and should always be purchased in opaque bottles that have been kept refrigerated. Flaxseed oil should have a sweet nutty flavor. We never recommend the use of flaxseed oil in cooking, since it is far too easily oxidized. However, it's fine to add flaxseed oil to foods after they have been cooked. For more on our recommendations on flaxseed oil, see this Q+A.
"Cyanide" is a term that we typically associate with the potentially deadly poison, hydrogen cyanide. However, there are very small amounts of cyanide constantly present and undergoing metabolism in human tissue. These small amounts of cyanide are found in relatively non-toxic forms like thiocyanates. Of course, these same thiocyanates are also found to occur naturally in foods (for example, in cruciferous vegetables). Linamarin and lotaustralin are two of the primary cyanogenic glycosides in flaxseeds, and like the thiocyanates in cruciferous vegetables, both of these compounds can contribute to cyanide metabolism in humans. However, as long as our metabolic processes are not overloaded and we are in reasonably good health, about two tablespoons of flaxseeds per day are likely to provide too little linamarin and lotaustralin to cause an adverse reaction. We've seen research on flaxseed meal, for example, which shows about 5-6 milligrams of cyanogenic glycosides (CGs) in one tablespoon. (And to give you a comparison, oral doses of sodium cyanide and potassium cyanide that cause acute and dangerous toxicity in humans fall into the range of 1000's of milligrams.)
It's not actually the CGs themselves that pose a risk, but their breakdown by an enzyme called beta-glucosidase that results in the release of hydrogen cyanide. When beta-glucosidase is unavailable or ineffective in breaking apart the CGs, we don't get faced with the hydrogen cyanide risk. And even when beta-glucosidase does break apart the CGs, there's an enzyme in our body called rhodanase that can convert hydrogen cyanide into the relatively non-toxic form of thiocyanate.
The issue of cooking and CGs in flaxseeds is somewhat ambiguous. We've see one study in which the baking of flax-flour containing muffins at 230F for 15-18 minutes showed no CGs in the final product. That result would point to a helpful impact of cooking on cyanide-related risk. We've also seen a study in which the overnight soaking of cassava, fermentation of cassava, as well as boiling, steaming, and dry heating of cassava all resulted in decreased CG content, with decreases falling into a very wide range of 32-99% range. While cassava is a food which can have the exact same amount of CGs as flaxseed, and in some cases, much higher amounts, it is also a food that is less compact and more porous than flaxseeds, and it would be expected to respond differently to cooking. In one study on commercial processing of flax, 20-30 minutes of heating at 150-221F did not appear to alter the CG content of the seeds or the processed flaxseed flakes or flaxseed cakes. From all of these studies, our overall conclusion is as follows: you may well benefit from the cooking of flaxseeds as a way of decreasing your cyanide-related risks, but you also may have no compelling reason to do so, since (1) the amount of CGs contained in 1-2 tablespoons is relatively small; (2) not all CGs will get broken down by enzymes and converted into hydrogen cyanide; and (3) if hydrogen cyanide does get created, most healthy persons will be able to detoxify it when it is present in such relatively small amounts.
Some people have gastrointestinal symptoms, such as flatulence and bloating, when they first begin to incorporate flaxseeds into their diet. It is suggested to start with a small amount, such as one teaspoon, and slowly build yourself up to your intake goal. When increasing fiber intake in the diet, it is also a good idea to include fluid (water) intake as well.
Several animal studies (involving rats and mice) have raised questions about the safety of high-dose flaxseeds during pregnancy—not for the pregnant females, but for their offspring. "High-dose" in these animal experiments has meant flax intake as 10% of the total diet, or about 4 tablespoons of flaxseed for every 2,000 calories. Although it is impossible to generalize from animal studies to humans, we recommend that women who are pregnant (or considering pregnancy) consult with their healthcare providers if they are consuming or planning to consume flaxseeds in these high amounts.
Flaxseeds, ground, raw
GI: very low
|omega-3 fats||3.19 g||133||32.0||excellent|
|vitamin B1||0.23 mg||19||4.6||very good|
|copper||0.17 mg||19||4.5||very good|
|manganese||0.35 mg||18||4.2||very good|
|fiber||3.82 g||15||3.7||very good|
Density>=7.6 AND DRI/DV>=10%
Density>=3.4 AND DRI/DV>=5%
Density>=1.5 AND DRI/DV>=2.5%