Flaxseed - Overview of Benefits, Recommended Intake and Caution

For a brief overview, take a look at our Flaxseed - A Summary article. 

Flaxseed continues to be an increasingly popular ingredient, frequently added to meals and snacks due to its pleasant nutty taste, versatility, convenience and nutritional compositition[1-8].

The cultivation and consumption of flaxseed by humans can be traced as far back as 3000 BC, to the ancient kingdom of Babylon in modern-day Iraq, where the seeds were a valued food source and the fibres were used for linen production[9]. In the 8th century it is documented that King Charlemagne believed so strongly in the health attributes of flaxseed that he passed a law to command his staff to consume flaxseed daily[10]. Current research has provided evidence to credit the health benefits of past beliefs[3-8].

Flaxseed boasts an impressive nutrient profile (see Appendix 1), being a rich source of protein, fibre, essential fatty acids and vitamins. Flaxseed is a great source of the essential omega-3 fatty acid alpha linolenic acid (ALA), which can be converted to EPA and DPA by the body[11]. Read here for more information.

Flax is grown predominantly in moderate climates such as Russia, Belgium, Canada, China and Kazakhstan[12]. The fibres of the flax plant are used for the production of linen, a process leaving minimal waste[13]. When fully grown, the flax plant resembles that of long meadow grasses growing to approx. 1.2m in height and bears a five-petalled blue flower where the dry round fruit ripens, containing the flaxseed. The seeds can be eaten whole or milled, or they can be pressed to extract the oil for use in cooking, medicine and health care[14]. The grinding and milling processes prevent the seed from being damaged by oxidation; milling also increases the bioavailability of many nutrients as it breaks down the outer shell[15, 16]. Read here for how the flaxseed in Huel is produced.

Brown and golden flaxseed

The two crop varieties of flaxseed are brown and golden (yellow) flax. Canada predominantly grows brown flaxseed and areas such as South Dakota golden flaxseed[16]. Visually the varieties are easily distinguishable, and in taste comparisons, brown is often the more favourable choice due to its subtle nutty tones. However, the nutritional profiles of both are similar, with brown flaxseed having a slightly higher ALA content[18].

Phytoestrogens

Phytoestrogens (also known as polyphenol phytoestrogens) are bioactive molecules. As the name indicates, phytoestrogens are derived from plants (’phyto’ being Greek for plant) and have a chemical structure that is similar to but not the same as that of human oestrogen. Phytoestrogens are naturally present in many common foods such as vegetables, seeds, berries, wine and tea[19]. There are a variety of structurally different compounds such as isoflavones (mainly found in soya), lignans (flaxseed and grains) and stilbenes (in grape skin)[19]. Due to their structure, phytoestrogens have the potential to bind to the oestrogen receptor in humans and can act either like weak oestrogen promoters or inhibitors[20].

Cyanide compounds in foods

Cyanide is present in the environment: it’s in air, drinking water, some soil and some foods. Cyanide comes from organic sources such as cyanide-producing bacteria, algae and plants, and chemical sources such as industry and pesticides[21].

Plants that are able to liberate significant amounts of hydrogen cyanide (HCN) from the environment, through respiration, photosynthesis and through the soil, are referred to as ‘cyanogenic’[21]. Nearly 3,000 plant species have been reported to be cyanogenic: the most commonly consumed include almonds, cashews, cassava root, lima beans, spinach, millet, bamboo shoots, soya and flaxseed[21, 22]. Cyanide compounds in plant-based foods occur naturally and consist of alpha-hydroxynitriles and cyanogenic glucosides, called cyanohydrins[23]. The HCN and cyanide glycosides contained in plants and seeds support metabolic processes in the plant, aid the production of plant-based proteins and enzymes and are also believed to be produced to cause a bitter taste to ward off herbivores[21, 23].

You’re more likely to ingest these trace amounts of cyanide when such foods are consumed raw and dry, as heat and water breaks down the compounds. When flaxseed is eaten raw, the body has a natural capacity to break down a substantial amount of the cyanide compounds into thiocyanate which is expelled through urine and carbon dioxide when we breathe out[22, 23]. The low exposure from naturally occurring plant compounds will leave the body with 12-18 hours without causing any harm to health[22]. See Appendix 2 for the amount of HCN in certain foods.

Vitamin B12 is an essential micronutrient. A supplemental form of B12 is cyanocobalamin which is the active component bound to a cyanide molecule. Extensive trials have concluded that because the cyanide is bound within the structure of cyanocobalamin, the cyanide cannot harm human or animal health[24] and this form is highly stable[25]. Diets rich in protein have been shown to be protective and to aid clearance of cyanide from the body from both naturally occurring and chemical exposure[26, 27].

Inorganic cyanide was a main constituent of many strong pesticides, and their use has been banned or restricted in most countries. However, it is still used in industrial processes in Germany, Japan, Netherlands and the USA and has been found in some unregulated weed killer treatments; although leaching from such compounds is very low[28]. Similarly, cyanide can be found in water; exposure through drinking water (tap and bottled) is prevented by regular testing to ensure the levels of HCN do not exceed 0.02ppm[29]. To limit exposure, global law dictates that all chemical spillages must be reported and foods that have been treated with pesticides are subjected to strict food and contaminant testing laws with large penalties for those found to be in violation[28, 29]. Tobacco smoke is the most common cause of cyanide entering the body[25].

Flaxseed cyanide content has surfaced recently from the health warning from the Swedish ‘National Food Authority’ (NFA) who highlighted what is claimed to be a potential risk of cyanide poisoning from flaxseed if consumption exceeds two teaspoons per day[30]. The warning was released to the public to make consumers aware that flaxseed can produce HCN. However, the report also states (translated):

‘is very unlikely that you get in such a dose over crushed flaxseed. Acute poisoning symptoms can include headache, nausea, dizziness, confusion and numbness. Serious hydrogen cyanide poisoning can affect breathing. There are no published reports of acute hydrogen cyanide poisoning caused by crushed flaxseed’[30].

While it's essential to be aware of potential food toxicity, in this instance, the warning is overly cautious and unnecessary. Sweden is the only country globally that has raised a concern regarding HCN levels in flaxseed. To support this evaluation, several studies have no reported incidence of toxicity[6, 31].

Flaxseed and health

The nutritional profile of flaxseed have been examined and demonstrated to overwhelmingly aid the maintenance of health in the general population. The publications highlighting possible adverse effects from phytoestrogens and cyanide have been based on assumptions or on rodent trials, rather than on how the compounds are broken down or taken up in the human body. As described above, the body has mechanisms to break down and eliminate phytoestrogens and HCN. While it is important to be aware of and to take health warnings seriously, the evidence does not support the notion that flaxseed is deleterious to human health; in fact, evidence supports the overwhelming benefits of consuming flaxseed regularly.

Appendix 1

Table 1: Nutritional value of brown flaxseed per 100g

Nutritional value per 100g

Energy 450 kcal
Carbohydrate 30g
Sugar 1.6g
Dietary fibre 27g
Fat 37g
Saturated 3.7g
Monounsaturated 7.5g
Polyunsaturated 28.7g
omega-3 22.8g
omega-6 5.9g
Protein 30g

Table 2: Micronutrient profile of brown flaxseed per 100g

Thiamin (B1) 0.53 mg/100g
Riboflavin (B2) 0.23 mg/100g
Niacin (B3) 3.21 mg/100g
Pyridoxine (B6) 0.61 mg/100g
Pantothenic acid (B5) 0.57 mg/100g
Folate (B9) 112 µg/100g
Biotin (B7) 6 µg/100g
Vitamin E 569 µg/100g
Potassium 813 mg/100g
Sodium 24 mg/100g
Calcium 255 mg/100g
Iron 5.7 mg/100g
Magnesium 392 mg/100g
Phosphorus 642 mg/100g
Zinc 4.34 mg/100g

Appendix 2

Table 3: Hydrogen cyanide (HCN) content mg/kg in commonly consumed foods[21, 22]

Food HCN mg/kg
Flaxseed 360-390
Lima beans 2500
Bamboo shoots 2500-500
Apple seed 750
Peach kernel 800
Plum kernel 700
Cherry juice 4.6
Bitter almond 4700
Nectarine 200

References

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  15. Przybylski R, et al. Storage stability of milled flaxseed. J Amer Oil Chem Soc. 2000; 78.
  16. Kuijsten A, et al. The Relative Bioavailability of Enterolignans in Humans Is Enhanced by Milling and Crushing of Flaxseed. The Journal of Nutrition. 2005; 135(12):2812-6.
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  18. Nitrayová S, et al. Amino acids and fatty acids profile of chia (Salvia Hispanica L.) and flax (Linum Usitatissimum L.) seed. Potravinarstvo Sci J for Food Industry. 2014; 8(1):72-6.
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