Flaxseed as a functional food source

Flaxseed is emerging as one of the key sources of phytochemicals in the functional food arena.  In addition to being one of the richest sources of a to linolenic acid oil and lignans, flaxseed is an essential source of high to quality protein and soluble fibre and has considerable potential as a source of phenolic compounds.  The implications of diets containing flaxseed or its components for human nutrition and disease prevention are analysed in this paper.  Results of the first meta analysis examining the relationship between intake of flaxseed or its components and risk reduction of disease in humans is presented.  Some areas of potential opportunities and impact of using flaxseed or its components in the diet are highlighted. (Authors abstract)

Flaxseed consumption in various forms as a food ingredient and for its medicinal properties dates from 5000 BC since its cultivation.  It is therefore not surprising that flaxseed is the most prominent oilseed studied to date as a functional food, since it is a leading source of the  n3 fatty acid a linolenic acid (ALA) (52  percent of total fatty acids) and of phenolic compounds known as lignans ( greater than 500ug, as is basis).  These and other components of flaxseed incorporation in the diet are particularly attractive for the development of foods with specific health advantages. The demonstration of clinical activity associated with the consumption of flaxseed led the US National Cancer Institute (NCI) to target flax as one of the six plant materials for study as cancer to preventative foods.  A computerised literature search on Medline was performed to identify trials assessing clinical end to points of intake of flaxseed or its components in reducing the risk of diseases.  This systematic review of the effectiveness of flaxseed and its components on humans identified 24 clinical studies, 11 of which involved flaxseed oil.  However, only 12 studies, six each with flaxseed and flaxseed oil, involving a total of 208 people, met all the criteria of well to designed clinical trials.
Collectively, the results generated by three studies on lipid metabolism suggest that flaxseed oil does not alter serum chemistry, but, in large doses, triacylglycerol levels are reduced.  The clinical relevance of the hypothesis that ALA of flaxseed oil protects against cardiovascular disease is considerable and is supported by four studies.  Thus a simple addition of flaxseed oil to canola oil in a 1:3 ratio can beneficially mediate the effects of ALA on the eicosanoids, producing significant reduction in the risk of cardiovascular disease.  Flaxseed oil is a potent inhibitor of pro to inflammatory mediators even when used in domestic food preparation.  This advantage of flaxseed oil can be positively utilised in the development of novel anti to inflammatory therapies  with or without pharmaceutical products for target populations.
Three studies concluded that consumption of flaxseed either raw or defatted reduces total and LDL cholesterol in humans, confirming the multicomponent cardioprotective effect of flaxseed.  In addition to the hypocholesterolaemic effect, flaxseed confers beneficial renal function in patients suffering from lupus nephritis, is well tolerated and does not compromise antioxidant status.  Studies in women show the vital role of flaxseed in mediating bone health and its strong phytoestrogenic and therapeutic effect in reducing the risk of hormone to related cancers.  This systematic review supports other epidemiological studies indicating that consumption of flaxseed may be protective against coronary heart disease, immune to renal injury and hormonal cancers.
When the results from the meta analysis and patent search are compared, the lack of clinical studies on flaxseed gum and protein becomes clearly evident.  One reason for this dearth of clinical studies on flaxseed gum and protein may be the increased understanding of, and belief in, secondary plant substances as the only bioactive phytochemicals.  Both protein and gums are abundant major components of flaxseed and as such would be the most economical targets for functional foods.  Flaxseed gum has nutritional value as a dietary fibre; as such it appears to play a role in reducing diabetes and coronary heart disease risk, preventing colon and rectal cancer and reducing the incidence of obesity.  Flaxseed gum behaves like typical viscous fibres with the ability to reduce blood glucose response and flatten blood glucose profile.  Reducing blood glucose response contributes to improving overall blood glucose control and is likely to be beneficial for individuals with glucose intolerance.
Flaxseed protein may also influence blood glucose because of its interaction with the gums and also by stimulating insulin secretion, resulting in reduced glycaemic response.  The interaction between flaxseed protein and soluble polysaccharides may play a significant role in reducing colon luminal ammonia, thereby protecting against the known tumour to promoting effects of ammonia.  Lignans are also known to have strong protein to binding properties, which may suggest some partial chemopreventive effect of flaxseed in conjunction with lignans.  Proteins with high levels of branched to chain amino acids (BCAA: valine, leucine, isoleucine), low content of aromatic amino acids (AAA) and high Fischer ratio (BCAA/AAA) are being sought for producing physiologically functional foods for specific needs, such as in patients with malnutrition associated with cancers, burns, trauma and liver failure, and for nutritional support of children with chronic or acute diarrhea or milk protein allergies.  Flaxseed protein and its individual fractions are high in BCAA and Fischer ratio, comparable to that of soybean.  Some flaxseed protein fractions with BCAA and Fischer ratio as high as 25g per 100g protein and 4.7 respectively provide the desirable levels required in diet formulations for patients with liver disease.   Flaxseed protein is also an excellent source of arginine, glutamine and histidine, the three amino acids known to have strong effects on the immune functions of the body.  The high cysteine and methionine content of flaxseed proteins can boost the body’s antioxidant levels, potentially stabilising DNA during cell division and reducing the risk of certain forms of colon cancer.
The most researched biological activities of flaxseed have been relegated to ALA, lignans and, to a lesser extent, soluble polysaccharides (gum), since flaxseed is the most abundant prominent source of these components.  However, most of the human studies to date that show beneficial effects have used whole flaxseed, flaxseed flour or defatted flaxseed meal, ie products of commerce.    Accurate documentation of the therapeutic effects of flaxseed and its components that contribute uniquely to disease prevention, health protection and as a deterrent to degenerative diseases will increase its potential for use as a functional food and food ingredient. (Editors Comments)