The Health Benefits of Flaxseed

Just what is flaxseed? We take a nutritional deep dive into the popular ingredient, busting some myths and highlighting some key flaxseed benefits. 

Flaxseed continues to be an increasingly popular ingredient, frequently added to meals and snacks due to its pleasant nutty taste, versatility, convenience and health-beneficial properties^[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]. Through to present day, flaxseed has seen a large increase in use and demand due to the evidence of health-protecting properties. Flaxseed particularly has been attributed to reduction of risk of diabetes mellitus, obesity, some cancers and heart disease^[11].

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^[12]. Read here for more information.

What is flaxseed made of?

Flax is grown predominantly in moderate climates such as Russia, Belgium, Canada, China and Kazakhstan^[13]. The fibres of the flax plant are used for the production of linen, a process leaving minimal waste^[14]. 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^[15]. 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^{[16, 17]}. Read here for how the flaxseed in Huel is produced.

What Are The Key Health Benefits of Flaxseed?

Flaxseed is packed with nutrients, fibre and omega-3 fatty oils

As referenced earlier, flaxseed is a rich source of protein, fibre, vitamins and the essential omega-3 fatty acid alpha-linolenic acid (ALA), which can be converted to EPA (eicosapentaenoic acid) and DPA (docosapentaenoic acid) by the body^[12].

It may help lower blood pressure

Regular consumption of flaxseed may reduce high blood pressure ^[54] - 11 large studies concluded that daily consumption of flaxseed for 3 months lowers blood pressure to a level which can significantly reduce the risk of heart disease and stroke.

Flaxseed, lignans and cancer

Evidence credits the ingestion of phytoestrogens with protective qualities against a range of health problems including breast, bowel and prostate cancers, cardiovascular disease, cognitive deterioration and osteoporosis^[22].They have also been shown to reduce menopausal symptoms and side effects of polycystic ovary syndrome (PCOS)^{[22, 23]}.These benefits largely stem from lignans which have a high antioxidant content that protect cells from free-radical damage^[8].

Flaxseed has the highest concentration of lignans, containing up to 800 times more than other plant species^[23]. Lignans play an important role in plant growth and act as antioxidants in human metabolism. The lignans from flaxseed are converted in the colon into the mammalian lignans enterodiol and enterolactone via gut bacteria. Enterodiol and enterolactone function as antioxidants preventing cell damage^[5]. Lignans from flaxseed have been shown to decrease the risk of some cancerous development, have protective effects against chemotherapy to healthy cells^[8] and can lower low-density lipoprotein (LDL–‘bad’ cholesterol) levels^[24].

Plant lignans are converted into relatively weak oestrogenic compounds in the intestines via the gut flora^[25].These compete for binding sites with the much stronger endogenous and exogenous oestrogens^[26]. This process has shown to help reduce excessive hormonal stimulation on oestrogen-sensitive tissues, particularly offering a protective effect against breast and prostate cancers, reducing the requirement for hormone replacement therapy (HRT) in menopausal women and suppressing the overproduction of oestrogen in PCOS^[26].

Flaxseed, Phytoestrogens and Testosterone

Phytoestrogens are derived from plants and have a chemical structure that is similar to that of human oestrogen. Phytoestrogens are naturally present in many common foods such as vegetables, seeds, berries, wine and tea^[20].

There are a variety of structurally different compounds including lignans which are found in flaxseed and grains^[20]. Phytoestrogens can bind to the oestrogen receptor in humans and can act either like weak oestrogen promoters or inhibitors^[21].

Lignans play a role in plant growth and act as antioxidants in human metabolism. They are converted into weak oestrogenic compounds in the intestines via the gut flora which renders lignans inactive^[25]. Therefore, lignans present no effect on the body’s oestrogen levels^[26]. However, in chronic intestinal illness, the flora may have suboptimal binding abilities, potentially leading to a slight increase in oestrogen levels^[26].

Concern has been raised that the ingestion of phytoestrogens could alter the uptake of testosterone in males. However, these claims are unfounded and based on poorly designed studies on rodents that were administered large quantities of extracted phytoestrogens^[29].

There have been no reported medical cases of testosterone disturbance due to phytoestrogens in humans derived from dietary intake^[36] and the consumption of phytoestrogens from flaxseed does not appear to affect sex hormone metabolism.

Flaxseed and Cyanide Compounds in Foods

Cyanide is naturally present in the environment and plants that are able to liberate hydrogen cyanide (HCN) are referred to as ‘cyanogenic’^[42]. Nearly 3,000 plant species have been reported to be cyanogenic: the most common include almonds, soya and flaxseed^{[42, 43]}, where they occur naturally^[43].

You’re more likely to ingest these trace amounts of cyanide when such foods are consumed raw and dry, as heat and water degrade these compounds. When flaxseed is eaten raw, the body has a natural capacity to break down cyanide compounds which are expelled through urine and breath without any harm to health^{[42, 55].}

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 ^[42].

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’^[42].

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^{[42, 43]}. Cyanide compounds in plant-based foods occur naturally and consist of alpha-hydroxynitriles and cyanogenic glucosides, called cyanohydrins^[44].

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^{[42, 44]}.

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^{[43, 44]}. The low exposure from naturally occurring plant compounds will leave the body with 12-18 hours without causing any harm to health^[43]. 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^[45] and this form is highly stable^[46]. 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^{[47, 48]}.

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^[49].

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^[50]. 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^{[49, 51]}. Tobacco smoke is the most common cause of cyanide entering the body.^[42].

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^[52]. 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’^[52].

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, studies in 2008 and 2009 concluded that 40g of flaxseed per day saw the participants achieve the maximum health benefits without any adverse effects^[52].

Also studies in 1994 and 1995 showed observations in improved health status in all participants who consumed 50g of raw flaxseed per day^[6]; improvements were particularly noted in cardiovascular and respiratory health, improved blood glucose and cholesterol ratios, improved digestive health and weight compared with those who did not consume flaxseed. Furthermore, there was no reported incidence of toxicity^{[6, 53]}.

In mid-2019 the British media picked up on an EFSA report and suggested that a third of a teaspoon could lead to poisoning in children. The EFSA later addressed these concerns stating that the results had been misinterpreted and that there has yet to be a case of flaxseed poisoning^[53].

The flaxseed in Huel is cold-pressed, milled, packaged and stored under special conditions and subjected to regular ‘critical control points’ (CCP) to ensure that all the valuable nutrition and health attributes are preserved. For those who regularly consume Huel there need not be any concern about HCN levels, as the quantity of flaxseed is well within the lower range of that which is deemed safe for human consumption. Based on research findings, cyanide compounds in flaxseed leave the body via the urine and are expelled along with carbon dioxide^[43].

Are There any Health Risks From Consuming Flaxseed?

Myth: Flaxseed Can Cause Poisoning

In mid-2019 the British media picked up on an EFSA report and suggested that a third of a teaspoon could lead to poisoning in children. The EFSA later addressed these concerns stating that the results had been misinterpreted and that there has yet to be a case of flaxseed poisoning^[52].

The flaxseed in Huel is cold-pressed, milled, packaged and stored under special conditions and subjected to regular ‘critical control points’ (CCP) to ensure that all the valuable nutrition and health attributes are preserved. For those who regularly consume Huel there need not be any concern about hydrogen cyanide (HCN) levels, as the quantity of flaxseed is well within the lower range of that which is deemed safe for human consumption. Based on research findings, cyanide compounds in flaxseed leave the body via the breath, and urine, and are expelled along with carbon dioxide with no negative health effects^[53].

Myth: Ingesting Flaxseed Phytoestrogens Can Alter Testosterone Uptake

Concern has been raised that the ingestion of phytoestrogens could alter or inhibit the uptake of testosterone or exhibit pro-oestrogenic effects, particularly in males. However, as discussed earlier, these claims are unfounded.

The consumption of phytoestrogen from flaxseed does not appear to affect sex hormone metabolism in males or females, principally due to the phytoestrogens from flaxseed being lignans rather than isoflavones^{[40, 41]}.

Flaxseed in Huel

Flaxseed is a key ingredient in most of our products, from Huel V3.0 to Huel Complete Protein Bars. The flaxseed in Huel products is subjected to a variety of quality controls in order to ensure that all the valuable nutrition in this nutritional powerhouse is preserved.

Flaxseed Health Benefits: Summary

The health benefits of flaxseed have been examined and demonstrated to overwhelmingly aid and protect human health. 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

Table 2: Micronutrient profile of brown flaxseed per 100g

Appendix 2

Table 3: Hydrogen cyanide (HCN) content mg/kg in commonly consumed foods^{[42, 43]}

References

1. Hargis PS & Van Elswyk ME. Manipulating the fatty acid composition of poultry meat and eggs for the health conscious consumer. World's Poultry Sci J. 1993; 49(3):251-64.
2. Prasad K. Flaxseed and cardiovascular health. J Cardiovascular Pharma. 2009; 54(5):369-77.
3. Biswas AK, et al. Dietary fibres as functional ingredients in meat products and their role in human health. Int J Livestock Production. 2011; 24:45-54.
4. Rabetafika HN, et al. Flaxseed proteins: food uses and health benefits. Int J Food Sci and Tech. 2011; 46(2):221-8.
5. Kitts DD, et al. Antioxidant activity of the flaxseed lignan secoisolariciresinol diglycoside and its mammalian lignan metabolites enterodiol and enterolactone. Mol Cell Biochem. 1999; 202(1-2):91-100.
6. Cunnane SC, et al. Nutritional attributes of traditional flaxseed in healthy young adults. Am J Clin Nutr. 1995; 61(1):62-8.
7. Oomah BD. Flaxseed as a functional food source. J Sci of Food and Agri. 2001; 81(9):889-94.
8. Toure A & Xueming X. Flaxseed lignans: source, biosynthesis, metabolism, antioxidant activity, bioactive components, and health benefits. Comp Rev in Food Sci and Food Safety. 2010; 9(3):261-9.
9. Bedigian D & Harlan JR. Evidence for cultivation of sesame in the ancient world. Econ Botany. 1986; 40(2):137-54.
10. Morris DH, et al. Flaxseed. In: Caballero BF, P, et al., editors. Encyclopedia of Food Sciences and Nutrition 2nd ed: Academic Press, New York; 2003. p. 2525-31.
11. Cardoso Carraro JC, et al. Flaxseed and Human Health: Reviewing Benefits and Adverse Effects. Food Revs Int. 2012; 28(2):203-30.
12. Harper CR, et al. Flaxseed oil increases the plasma concentrations of cardioprotective (n-3) fatty acids in humans. J Nutr. 2006; 136(1):83-7.
13. Nag S, et al. An overview on flax (Linum usitatissimum L.) and its genetic diversity. Int J Agric, Environ and Biotech. 2015; 8(4):805.
14. Dissanayake NPJ, et al. Energy Use in the Production of Flax Fiber for the Reinforcement of Composites. J Natural Fibers. 2009; 6(4):331-46.
15. Goyal A, et al. Flax and flaxseed oil: an ancient medicine & modern functional food. J Food Sci Technol. 2014; 51(9):1633-53.
16. Przybylski R, et al. Storage stability of milled flaxseed. J Amer Oil Chem Soc. 2000; 78.
17. 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.
18. Flax Council of Canada. Brown Flax Seeds, or Golden? Date Accessed: 06/11/20. [Available from: https://flaxcouncil.ca/resources/nutrition/general-nutrition-information/brown-flax-seeds-or-golden/]
19. 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.
20. Gaya P, et al. Phytoestrogen metabolism by adult human gut microbiota. Molecules. 2016; 21(8):1034.
21. Morito K, et al. Interaction of phytoestrogens with estrogen receptors alpha and beta. Biol Pharm Bull. 2001; 24(4):351-6.
22. Rietjens IMCM, et al. The potential health effects of dietary phytoestrogens. Br J Pharmacol. 2017; 174(11):1263-80.
23. Khani B, et al. Effect of soy phytoestrogen on metabolic and hormonal disturbance of women with polycystic ovary syndrome. J Res Med Sci. 2011; 16(3):297-302.
24. Pan A, et al. Meta-analysis of the effects of flaxseed interventions on blood lipids. The American journal of clinical nutrition. 2009; 90(2):288-97.
25. Selma MV, et al. Interaction between phenolics and gut microbiota: role in human health. J Agric Food Chem. 2009; 57(15):6485-501.
26. Desmawati D, et al. Phytoestrogens and Their Health Effect. Open Access Maced J Med Sci. 2019; 7(3):495-9.
27. Christiansen K. Behavioural correlates of testosterone. Testosterone. Berlin, Heidelberg: Springer; 1998. p. 107-42.
28. Probst F, et al. Testosterone-to-oestradiol ratio is associated with female facial attractiveness. Q J Exp Psychol (Hove). 2016; 69(1):89-99.
29. Weber KS, et al. Dietary soy-phytoestrogens decrease testosterone levels and prostate weight without altering LH, prostate 5alpha-reductase or testicular steroidogenic acute regulatory peptide levels in adult male Sprague-Dawley rats. J Endocrinol. 2001; 170(3):591-9.
30. Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment. Phytoestrogens and Health. London, England: FSA; 2003.
31. Qin W, et al. Soy isoflavones have an antiestrogenic effect and alter mammary promoter hypermethylation in healthy premenopausal women. Nutr Cancer. 2009; 61(2):238-44.
32. Haun CT, et al. Soy protein supplementation is not androgenic or estrogenic in college-aged men when combined with resistance exercise training. Scientific reports. 2018; 8(1):11151.
33. Jargin SV. Soy and phytoestrogens: possible side effects. Ger Med Sci. 2014; 12:Doc18-Doc.
34. Ahtiainen JP, et al. Muscle hypertrophy, hormonal adaptations and strength development during strength training in strength-trained and untrained men. Eur J Appl Physiol. 2003; 89(6):555-63.
35. Atherton PJ, et al. Muscle protein synthesis in response to nutrition and exercise. The Journal of physiology. 2012; 590(5):1049-57.
36. Adlercreutz H, et al. Effect of dietary components, including lignans and phytoestrogens, on enterohepatic circulation and liver metabolism of estrogens and on sex hormone binding globulin (SHBG). J Steroid Biochem. 1987; 27(4-6):1135-44.
37. Allen NE, et al. Hormones and diet: low insulin-like growth factor-I but normal bioavailable androgens in vegan men. Brit J Cancer. 2000; 83(1):95-7.
38. Erol A, et al. Sex hormones in alcohol consumption: a systematic review of evidence. Addict Biol. 2019; 24(2):157-69.
39. Cleary MP, et al. Minireview: Obesity and breast cancer: the estrogen connection. Endocrinology. 2009; 150(6):2537-42
40. Demark-Wahnefried W, et al. Flaxseed supplementation (not dietary fat restriction) reduces prostate cancer proliferation rates in men presurgery. Cancer Epidemiol Biomarkers Prev. 2008; 17(12):3577-87.
41. Hutchins AM, et al. Flaxseed consumption influences endogenous hormone concentrations in postmenopausal women. Nutr Cancer. 2001; 39(1):58-65.
42. Jaszczak E, et al. Cyanides in the environment-analysis-problems and challenges. Environ Sci Pollut Res Int. 2017; 24(19):15929-48.
43. Abraham K, et al. Bioavailability of cyanide after consumption of a single meal of foods containing high levels of cyanogenic glycosides: a crossover study in humans. Arch Toxicol. 2016; 90(3):559-74.
44. Gleadow RM, et al. Mini-Review: Constraints on Effectiveness of Cyanogenic Glycosides in Herbivore Defense. Journal of Chemical Ecology. 2002; 28(7):1301-13.
45. Conn JB, et al. The equilibrium between vitamin B12 (cyanocobalamin) and cyanide ion. Science. 1951; 113(2945):658-9.
46. Ahmad I, et al. Effect of ascorbic acid on the degradation of cyanocobalamin and hydroxocobalamin in aqueous solution: a kinetic study. AAPS PharmSciTech. 2014; 15(5):1324-33.
47. Simeonova F, et al. Hydrogen Cyanide and Cyanides: Human Health Aspects. Geneva, Switzerland: WHO. 2004 U.S. Department of Health and Human Services. Toxicological Profile for Cyanide. Atlanta, USA: Agency for Toxic Substances and Disease Registry. 2006.
48. Agency for Toxic Substances & Disease Registry. Public Health Statement For Cyanide. Atlanta, GA, U.S: Department of Health and Human Services. 2006.
49. National Research Council (US) Safe Drinking Water Committee. Drinking Water and Health: Volume 1. Washington (DC): National Academies Press (US). 1977.
50. Donato DB, et al. Heap leach cyanide irrigation and risk to wildlife: Ramifications for the international cyanide management code. Ecotoxicol Environ Saf. 2017; 140:271-8.
51. The Swedish National Food Agency. Cyanogenic glycosides and hydrogen cyanide. Date Accessed: 06/11/20. [Available from: https://www.livsmedelsverket.se/livsmedel-och-innehall/oonskade-amnen/vaxtgifter/cyanogena-glykosider-och-vatecyanid].
52. Bloedon LT, et al. Flaxseed and cardiovascular risk factors: results from a double blind, randomized, controlled clinical trial. J Am Coll Nutr. 2008; 27(1):65-74.
53. Morrison O. FoodNavigator. Date Accessed: 12/11/20. [Available from: https://www.foodnavigator.com/Article/2019/08/21/Europe-s-food-safety-watchdog-plays-down-flaxseed-cyanide-danger#]
54. Khalesi, S., Irwin, C. and Schubert, M., 2015. Flaxseed Consumption May Reduce Blood Pressure: A Systematic Review and Meta-Analysis of Controlled Trials.
55. Moknatjou R, et al. Roasting effect on total cyanide, α-tocopherol and oil characteristics of the brown and yellow types of the flaxseed (Linum Usitatissimum L.). Int J Biosci (IJB). 2015; 6(5):273-82.