Nutrition Myths
Benefits of flaxseed

SUMMARY

  • For optimal health benefits, eat 20-50 g of milled flaxseeds per day.
  • Most of benefits of flaxseed are related to their high contents of fiber, lignans and antioxidants.
  • Flaxseeds are good for digestive health.
  • Flaxseed intake can also lower cholesterol, inflammation and oxidative stress, control blood sugar levels, regulate hypertension, decrease the risk of type 2 diabetes, atherosclerosis, cardiovascular disease and sex hormone related cancers and lower menopause symptoms.
  • By reducing appetite and, therefore, food intake, flaxseed consumption mainly results in weight loss. More studies are needed.
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Benefits of flaxseed – evidence based

This article discusses the most publicized health benefits of flaxseed and the evidence behind the common health claims. 

Flaxseeds are one of the most nutritious foods. Their benefits are not only related to health – they are cheap, versatile and an easy to incorporate functional food.

Flaxseeds are considered a functional food, since they are rich in bioactive components, such as alpha-linolenic acid (ALA), lignans, dietary fiber, protein, soluble polysaccharides, phenolic compounds, vitamins and minerals.

Flaxseeds have been historically used for constipation, upper respiratory infections, abdominal pain, urinary infections and skin inflammation.

Flaxseeds have recently been popularized, due to their high omega 3 fatty acid content and concentration of nutrients.

While there are many health benefit claims of flaxseed, scientific studies are usually conflicting, and the evidence is weak.

There are potential health benefits, especially due to the high concentration of nutrients and antioxidants, but good quality clinical trials are needed to confirm these claims. (1)

This article lists the most common claims that have been investigated by scientific studies.

I ignored numerous far-fetched allegations, that have no scientific background.

NOTE: This article relates to the brown flaxseed, not the golden type, which has a different oil composition. Yellow/golden seeds have very low omega 3s and are usually not used for human consumption. (2)

How much flaxseed should you eat for maximum health benefits?

The health benefits of flaxseeds achieve the best results with dosages of between 20-50 grams of per day. (3, 4, 5)

Amounts of 50 g or more per day have unknown long-term effects and may potentially lead to toxicity. However, more studies are needed.

Note that the sudden increase in fiber intake may also cause side-effects, such as bloating and flatulence in the intestine. (For more information on the negative effects of flaxseed consumption, click here).

For this reason, it is best to gradually introduce (e.g. 1 teaspoon of milled seeds) and then slowly increase flaxseeds in your diet.

MAIN POINTS

  • Most studies suggest that the optimal amount of flaxseeds is 20-50 g per day
  • Increase the flaxseed intake gradually, starting with small amounts, to avoid gastrointestinal discomfort

Flaxseed – nutrition composition

Flaxseed is a nutrient – dense food.

  • 7g = 1 tbsp of flaxseed meal (a unit of measurement)
  • 28g ~ 1oz = 4 tbsp of flaxseed meal.

The following nutrition information is shown for 1oz = 4 tbsp = 28 g of flaxseeds seeds.

MICRONUTRIENTS

Excellent amounts of (>=20% of RDA):
Iron (Fe): 1.6 mg (20% of the RDA for men and 9% for women)
Magnesium (Mg): 110 mg (26% of the RDA for men and 34% for women)
Manganese (Mn): 0.7 mg (30% of the RDA for men and 39% for women)
Thiamin (Vit B1): 0.5 mg: (42% of the RDA for men, 46% for women)
Copper (Cu): 0.3 mg (33.3% of the RDA for both men and women)

Good amounts of 
(between 10 and 20% of RDA):
Phosphorus (K): 180 mg (18% of the RDA for both men and women)
Selenium (Se): 7.1 mcg (10% of the RDA for men and 12% for women)
Zinc (Zn): 1.2 mg (10.9% of RDA for men and 15 of RDA for women)

It contains significant amounts of calcium, potassium, niacin, vitamin B6, folate and choline.

MACRONUTRIENTS

Protein: 5.1 g
Carbohydrates (digestible carbohydrates) ~ 1 g
Fiber: 7.6 g (25% of the RDA for men, 30% for women)
Total Fat: 11.8 g of which Omega 3: 6.4 g (mostly ALA), Omega 6: 1.6 g

OTHER COMPOUNDS

Flaxseeds also contain high amounts of phenolic compounds, antioxidants and lignans.

MAIN POINTS

  • Flaxseeds are one of the most nutrient condensed foods
  • Flaxseeds are high in beneficial macronutrients, such as fiber, protein and ALAs and very low in digestible carbohydrates

Health benefits of flaxseed related to fiber

Flaxseeds are a great source of both soluble and insoluble dietary fiber. 1 oz. (28 g) of flaxseeds contains 7.6 g of fiber – 27% of the seed weight.

Official recommendations for daily fiber intake are of 38 g per day for men and 25 g for women. 1 oz. of flaxseeds is equivalent to 25% of the recommended dosage of fiber for men and 30.4% for women.

Depending on the source, it contains between 20-40% of soluble fiber and 60-80% of insoluble fiber.

The outer layer of a flaxseed contains mucilage, which has great health benefits. Mucilage contains 35%-45% of fiber and is 2/3 insoluble and 1/3 soluble.

Benefits of a high fiber diet:

  • It is prebiotic – feeds good gut bacteria and, therefore, improves intestinal health
  • Regulates blood sugar levels
  • Regulates cholesterol levels
  • May reduce the risk of colorectal cancer (more studies are needed)
  • Mucilage soaks up water, increasing its volume and stimulating bowel movements
  • Helps to relieve chronic constipation

MAIN POINTS

  • High fiber content in flaxseeds promotes good intestinal health and regular bowel movements
  • Fiber in flaxseeds may play an important role in reducing the risk of diabetes and cardiovascular diseases

Health benefits of flaxseed related to lignans and other phenolic compounds

Phenolic compounds and antioxidants are responsible for most of the health benefit of flaxseeds.

Flaxseeds are rich in phenolic compounds, such as lignans, phenolic acid, p-Coumaric acid, flavonoids, phenylpropanoids and tannins.

Their antioxidant action prevents oxygen radical production and are, therefore, helpful in reducing atherosclerosis and have anticarcinogenic properties. (6)

Lignans are phytoestrogens, a substance in plants that have similar effects to estrogen, the female sex hormone.

Flaxseed contains 75-800 times more lignans than other fiber rich plant, such as grains, legumes, fruit and vegetables. (7)

500mg of lignan per day for 8 weeks protects individuals from cardiovascular diseases and metabolic syndrome by lowering blood pressure, blood sugar, lipid concentration, inflammation and oxidative stress.

The flaxseeds’ lignans prevent cellular changes that lead to cancer formation and reduce metastasis.  (8, 9)

Note: although the lignans component of flaxseed acts against cancers related to sex hormones, studies show that ALAs, also high in flaxseeds, may increase the risk of prostate cancer. Therefore, high amounts of flaxseeds are not recommended in men, especially those with prostate cancer or a family history of prostate cancer.

MAIN POINTS

  • Lignans, abundant in flaxseeds, have many health benefits, such as reducing blood pressure, blood sugar, lipid concentration, inflammation and oxidative stress
  • Lignans are associated with a decreasing hormone-related cancer risk
  • Flaxseed also contains compounds with antioxidant properties, which are protective against cardiovascular diseases, cancers and many other chronic diseases

Health benefits of flaxseed related to proteins

Flaxseeds contain approximately 21% protein. (6)

The amino-acids that are abundant in flaxseeds are beneficial to immune health, fighting fungal infections and inflammation, in reducing hypertension and diabetes and regulating blood cholesterol. (10, 11, 12)

Please note that although flaxseeds are rich in proteins, they have relatively low levels of some amino acids, such as cystine, methionine and lysine.

These are referred to as limiting, since they may limit the rate of protein synthesis, if insufficiently available from the diet.

Flaxseed, therefore, cannot be used as the sole source of amino-acids. Cystine, methionine and lysine need to come from other foods for a complete protein generation. (6)

MAIN POINTS

  • Although rich in protein, flaxseeds lack some amino acids that are important for protein synthesis and, therefore, shouldn’t be used as the sole protein source.
  • High amino-acid contents in flaxseeds are beneficial in improving immune health and preventing cardiovascular risk and type 2 diabetes.

Health benefits of flaxseed related to Omega 3s

The health benefits of flaxseed and chia seeds have been overestimated, due to the misconception about omega 3 properties.

Omega 3s in flaxseeds are not as be beneficial as once though

The popularity of flaxseeds and chia seeds skyrocketed a few decades ago, due to their exceptionally high omega 3 contents.  However, its importance has been exaggerated.

Here are a few facts explaining why:

  • Flaxseeds consist of about 40% fat, most of which is an essential fatty acid, that cannot be produced by the body.
  • Most of the omega 3 in flaxseeds are in the form of alpha linolenic acid (ALA). It is the second highest food source of ALAs, after chia seeds.
  • Recent studies have shown that not all omega 3s have the same health potential. While there is considerable evidence that other omega 3s, such as EPA and DHA, sourced mainly from fatty fish, possess plenty health benefits, the effects of ALA are still unknown. (13)
  • Studies don’t show significant health benefits associated with ALAs contained in these seeds. (14)

Known benefits of omega 3s in flaxseeds:

  • ALAs are generally not harmful for consumption in moderation. However, a high ALA consumption is associated with an increased risk of prostate cancer.
  • They decrease omega 6 : omega 3 ratio, which results in reduced inflammation.
  • They are a good and non-harmful source of energy.

How do you get the most of Omega 3s from flaxseeds?

The most concentrated ALAs are found in flaxseed oil.

However, the best way of eating flaxseeds for maximum ALA intake, is in the form of ground/milled flaxseeds.

Bioavailability (the proportion of the substance that is absorbed and has an active effect on your body) of ALA depends on the form by which flaxseeds are consumed.

The order of bioavailability from highest to lowest is: flaxseed oil, milled seeds and whole seeds.

MAIN POINTS

  • The health benefits of flaxseed due to omega 3 have been largely overestimated
  • Flaxseeds’ fatty acids are mostly composed of ALAs, which are not as beneficial as other omega 3s, such as DHA and EPA
  • ALAs are generally not harmful, and may be potentially beneficial, although more studies are needed (exception: men should limit consumption due to prostate cancer risk)
  • The most obvious benefit from ALAs in flaxseeds is the reduced the omega 6 : omega 3 ratio and they are a safe energy source.

Importance of the ratio of omega 6 to omega 3 in flaxseeds

Omega 6 fatty acids have pro-inflammatory properties, while omega 3 have anti-inflammatory properties.

While inflammatory reaction is required in case of injury or infection, chronic excessive inflammation is the major factor in most deadly and debilitating diseases, such as metabolic syndrome, diabetes, heart disease, autoimmune diseases, arthritis or Alzheimer’s.

The average Western diet consists of a high ratio of about 15:1 of omega 6 : omega 3, leading to this unwanted chronic excessive inflammatory state. (15, 16)

Decreasing that ratio, reduces inflammation in the body and suppresses the development of the the above-mentioned conditions. (15)

That is one of the reasons why dieticians recommend eating small fatty fish or taking omega 3 supplements.

Seeds, such as flaxseeds or chia seeds, are very high in omega 3 fatty acids. Even though these oils are mainly ALAs, supplementing with these super nutritious seeds reduces the omega 6 to omega 3 ratio.

MAIN POINTS

  • A high omega 6: omega 3 ratio in the diet leads to chronic inflammation associated with many serious medical conditions
  • Flaxseeds have a very low omega 6: omega 3 ratio

Health benefits of flaxseed related to constipation and diarrhea

Flaxseed is rich in fiber and has been shown to be very effective as a natural treatment  for constipation and as a natural laxative.

However, not all people with chronic constipation benefit from a high fiber diet. In some cases, reducing dietary fiber or stopping it all together may help. (17)

Insoluble fiber has a water binding property, which results in increasing the bulk. This property is useful in the treatment of constipation, IBS and diverticular disease. (18)

Soluble fiber, contained in the mucilage of flaxseeds (the flaxseed coating), increases the viscosity of the contents in the bowels, which improves the ease of passage and excretion. (18)

It may also be protective to the intestinal mucosa layer.

Before starting or increasing flaxseed intake, you should know that:

  • water intake must be also increased to avoid the opposite effect, such as the obstruction of the bowel and constipation.
  • when taken with other laxatives, flaxseeds may potentiate its laxative effects.

NOTE: In some cases, reducing fiber (hence flaxseed) intake may help in chronic constipation relief. (17)

MAIN POINTS

  • Flaxseed is beneficial as a laxative and effective in constipation treatment. due to its high soluble and insoluble fiber contents.

Health benefits of flaxseed related to weight loss

Flaxseed supplements, in the form of flax fiber drinks and tablets, suppress appetite and reduce food intake. (19) These effects may contribute to weight loss.

A 2017 systematic review shows that the consumption of 30 g or more of whole flaxseeds per day for more than 12 weeks, may contribute to weight reduction in overweight and obese individuals. (20)

Otherwise the evidence of weight loss effects of flaxseeds is weak, and more studies are needed.

MAIN POINTS

  • Fiber rich flaxseeds have been shown to reduce appetite and food intake. However, there is weak evidence that it may contribute to weight loss.

Health benefits of flaxseed related to blood pressure

According to some studies, flaxseeds are one of the most potent anti-hypertensive foods.

The following components of flaxseeds, or their synergetic, unique combination, contributes to this potent antihypertensive action (21):

  • ALA: has an anti-inflammatory action. Inflammation is associated with hypertension.
  • Lignans: promotes antioxidant action reducing free radicals. Free radicals increase hypertension risk.
  • Fiber: helps to regulate hypertension.
  • Peptides: inhibit the action of the angiotensin-converting enzyme, lowering blood pressure.

A 2013 study showed that after six months of 30 g milled flaxseeds per day supplementation, the systolic pressure dropped by about 10 mm Hg and diastolic pressure by about 7 mm Hg.

The results were even more significant for the systolic blood pressure drop in hypertensive individuals (as much as 15 mm Hg). (21)

A recent systematic review also found that the consumption of flaxseeds for 12 weeks, slightly reduces systolic (-1.77mm Hg) and diastolic (-1.58mm Hg) blood pressure. (22)

Also read How to lower blood pressure?.

MAIN POINTS

  • Eating milled flaxseeds may reduce blood pressure
  • The largest drops in high blood pressure are observed in hypertensive people
  • More studies are needed, due to the existence of some studies showing less significant effects

Health benefits of flaxseed related to atherosclerosis and cardiovascular disease

Flaxseeds contain antioxidants and have properties that may lower blood lipids, have anti-platelet formation properties and reduce the levels of oxygen free radicals. Therefore, flaxseeds may help in fighting against atherosclerosis and cardiovascular disease. (23, 24)

These effects are mainly due to omega 3 fatty acids and lignans in flaxseeds.

The evidence of the effects on atherosclerosis are is not strong.  More studies are needed.

MAIN POINTS

  • There are indications that flaxseeds may have anti-plaque formation effects. However, the evidence is still weak.

Health benefits of flaxseed related to ADHD symptoms

Although there is an association between ADHD and lower levels of omega 3s in the blood, the studies on omega 3 supplementation in ADHD treatment are inconclusive.

The potential benefit also relates to DHA and EPA found in fish oils, rather than the main constituent of flaxseeds, ALA.

See what are the most effective ADHD treatment methods.

MAIN POINTS

  • Flaxseeds are rich in ALAs, a type of omega 3s which are not associated with ADHD symptoms

Health benefits of flaxseed in menopause

Flaxseed lignans may act as estrogen, depending on the level of estrogen in the body.

When estrogen is low in the body, as in the case of postmenopausal women, they act as a weak estrogen. (25, 26, 27)

However, flaxseeds may be an effective substitute for estrogen therapy in women experiencing hot flashes.

A study on women experiencing at least 14 flashes per week, showed an average decrease of 57% of hot flashes with 40 g of crushed flaxseeds per day and no medications.

More studies are needed.

MAIN POINTS

  • Lignans may act as a weak estrogen in postmenopausal women
  • Flaxseeds may be an effective dietary therapy in women experiencing hot flashes

Health benefits of flaxseed related to blood cholesterol levels

Soluble gum of flaxseeds has cholesterol lowering effects. (28, 29)

Partially defatted flaxseeds may be effective in lowering LDL cholesterol, reducing lipoprotein (a) and improving insulin sensitivity in adults with high cholesterol. (30, 31, 32, 33, 34, 35, 36, 37)

The cholesterol lowering effects of flaxseeds are due to their fiber and lignans contents. Fiber and lignans bind to bile acids, which contain cholesterol, and transport them through the intestine  until they are excreted.

Drinks enriched with flax fiber are much more effective in lowering cholesterol than bread enriched with fiber. (38)

MAIN POINTS

  • Fiber and lignans in flaxseeds may have cholesterol lowering effects.
  • It is yet to be shown if the consumption of flaxseeds lowers the small, dense lipoprotein and, therefore, the risk of atherosclerosis.

Health benefits of flaxseed related to cancer

Flaxseed and flaxseed oil can suppress tumor growth at a later stage of cancer.  Overall, they may be beneficial in cancer prevention, with the exception of prostate cancer.

There are several properties of flaxseeds that are associated with the potential positive and negative effects on cancer.

Lignans and antioxidants

The high amounts of phenolic compounds, such as phenolic acids, flavonoids and lignans, in flaxseeds have anti-cancer and antioxidative properties. (39, 40)

Lignans inhibit the growth of new tumors, especially the hormone-sensitive ones (e.g. breast, endometrium and prostate).

How does it work?

Lignans lower estrogen hormones in blood.

Since high blood estrogen is associated with an increased risk of several cancers related to sex hormones, consumption of flaxseeds may reduce that risk.

Lignans stimulate the production of a sex hormone binding globulin. This compound binds sex hormones and removes them from blood circulation. This reduces the biological activity of these hormones and, therefore, lowers the risk of developing cancer. (41)

Lignans, enterodiol and enterolactone have been linked to reduced risk of prostate cancer. (42)

The flaxseed lignans (or more specifically their metabolites) can prevent cellular changes, leading to cancer formation and reduce metastasis. (8, 9)

High omega 3 to omega 6 ratio

Eating flaxseeds and adding flaxseed oil to food, increases the omega 3 to omega 6 ratio (see section below).

A high omega 3 to omega 6 ratio in the blood has anti-inflammatory properties and reduce the risk of colorectal and breast cancers.

Alpha Linolenic Acids (ALAs)

Some studies show that tumors incorporate ALA into their composition, suppressing the growth of tumor cells.

However, some studies show that high amounts of ALAs may increase the risk of developing cancer. (43, 44)

Generally, it is advised that men should not consume high amounts of flaxseeds or flaxseed oil.

MAIN POINTS

  • Flaxseed consumption may reduce some hormone-related cancers.
  • The main anti-carcinogenic benefits of flaxseed are related their high contents of lignans and omega 3 to omega 6 ratio.
  • Studies on prostate cancer are conflicting, therefore, it is advisable for men not to eat high amounts of flaxseeds.
  • Flaxseeds may suppress new tumor growth and suppress the growth in late stage tumors.

Health benefits of flaxseed in blood sugar control and type 2 diabetes

Some studies show that flaxseed consumption may reduce fasting blood sugar (45), while other studies show no effects. (46)

With almost no digestible carbohydrates (about 1.5%) and high amounts of fat and fiber, flaxseeds have a zero Glycemic Index and Glycemic Load and, therefore, are diabetes friendly.

A recent systematic review has found that the consumption of whole seeds for more than 12 weeks, significantly reduces blood glucose and improves insulin resistance and sensitivity checks (reduces HOMA-IR and increases QUIKI).  Another important health benefit of flaxseed consumption is the improvement of insulin sensitivity. (47)

Overall, flaxseed consumption has either neutral or positive effects on blood sugar and insulin levels and is potentially beneficial in type 2 diabetes.

It is crucial to note that flaxseeds may interact with anti-diabetic medications, potentiating the effects of lowering blood sugar levels. Contact your doctor, if you are on these medications.

MAIN POINTS

  • Flaxseeds are either neutral or potentially beneficial for blood sugar and insulin control.
  • More studies are needed to demonstrate if it is effective in controlling type 2 diabetes.

Flaxseed benefits in culinary usage

Flaxseeds are very versatile in the kitchen. They can be added to just about anything, although their taste or texture, due to their ability to soak up water, may not suit some savory foods or desserts.

One tablespoon of ground flaxseeds weighs about 7 grams. If you use flaxseeds several times during the day, you can add one tablespoon a meal. (48)

Studies have shown that there are health benefits, when amounts of 20-50 grams per day are used.

Some nutrients, such as lignans and fiber, are not affected by cooking in high heat in normal cooking, and ALAs remain stable in cooking of up to 350 F (349C). (7, 49, 50, 51)

Here are a few examples of how you can use them:

  • Add flaxseeds to either cold or hot food in any form: whole or milled;
  • Add ground flaxseeds to breakfast cereals. They go very well with porridge, boiled rolled oats or toasted oats or other whole grains;
  • Add whole flaxseeds to soups, dips, spreads or salads. They will add a contrasting crunch;
  • Use whole or milled flaxseeds in baked products, such as breads, cakes, muffins or cookies. Baked products with added flaxseed-water mixture are gummy and chewy, and have lower than normal loaf volume;
  • Add the milled or whole flaxseeds to savory yogurt dishes or deserts;
  • Add milled flaxseeds to smoothies, adding extra liquid to compensate for the high absorption of the seeds;
  • Flaxseeds can be used as an egg substitute (beneficial for vegans or with egg allergy). To substitute one egg, add 15 g (one tablespoon) of milled flaxseed and 45 g (3 tablespoons) of water;
  • Add to ground meat dishes, such as meatballs and burgers, to substitute or in addition to breadcrumbs;
  • Flaxseed gum can be used in salad dressing as an emulsion (52);
  • Add to casseroles and stews.
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