January 31, 2008
Easily integrated into a variety of foods, and with health benefits that transcend omega-3 content, flaxseed strives to gain respect in a functional-foods world dominated by fish-derived EPA and DHA. Kelley Fitzpatrick, MSc, breaks down the formulation issues and explores the conversion controversy
Manufacturers, conscious of consumer demand for omega-3s, are seeking ways to improve the nutrient value of their food offerings. Two of the most popular sources for omega-3s are found in flaxseed and fish oil. Flax contains not only the omega-3 fatty acid alpha-linolenic acid (ALA), but also lignans, a major class of oestrogenlike compounds, antioxidants and fibre. Fish oils are sources of the long-chain omega-3s, eicosa-pentaenoic acid (EPA) and docosahexaenoic acid (DHA). Only by understanding the science supporting the full benefits of all three fatty acids (ALA, EPA and DHA) and the technology required to deliver a naturally stable functional food, can the best products be delivered to consumers.
Flax as a source of omega-3s is easily incorporated into both foods and beverages. Flax has been valued for decades by the bakery sector for its appearance and versatility, and the nutty flavor it imparts in food products. The interest in antioxidants and lignans, as well as flax's high-quality protein and fibre, is increasing the use of the seed in different food applications.
Flax is now found in prepared foods such as pastas and pizza crusts, smoothie beverages, dairy applications such as yoghurt, nutrition and weight-management bars, salad dressings, and breading systems. In many such applications, flax can replace unhealthy fats and white flour. In keeping with the desire of consumers for healthier-for-you foods and beverages, opportunities for flax will continue as food companies move toward the use of whole foods rather than the inclusion of expensive extracts, concentrates and oils. In all respects, flax offers a model for whole grains or seeds, and underscores the recognition given to the nutritional value of 'whole grains,' 'whole seeds' and 'whole foods.'
It is well accepted that foods prepared with long-chain polyunsaturated fatty acids have an increased vulnerability to rancidity, which is caused by oxidation, the chemical reaction of lipids with oxygen. EPA and DHA are particularly vulnerable to oxidative breakdown, leading to the development of food deterioration affecting flavour, aroma, colour, texture and nutritional value.
Although not as significant an issue, the stability of ALA in flax can be a problem if the seed has not been chosen and processed with care. The lipid in full-fat milled flaxseed is actually very stable when the seed has been carefully selected to remove discoloured and immature parts. Flax possesses an active antioxidant system that includes lignans, phenolic acids, anthocyanin pigments, phytic acid, and several flavonols and flavones. Reputable flax companies are able to guarantee stability of upwards of two years for milled flax that has been properly processed. Appropriate milling techniques can also prevent problems with texture and negative mouthfeel attributes. Ensuring adequate moisture levels in products using flax is critical due to the high levels of fibre present in the seed.
Stability has been an issue for omega-3 fortified foods using EPA and DHA, especially in applications such as toasted breads or extruded longer shelf-life products such as cereals and some prepared foods. These omega-3s have to date been most successfully incorporated into chilled food applications with a relatively short shelf life such as milks, juices, yoghurts, margarines and spreads.
Micro-encapsulation of omega-3s, especially EPA and DHA, has been, to date, the key technology in delaying or inhibiting oxidation, and thus helping to mask undesirable fishy odours and flavours in the final product. New patents are being filed regularly, and more food-ingredients companies are introducing new omega-3 products, usually in the form of emulsions or powders. They are marketed on the basis of an ability to deliver taste and odour neutrality in addition to other properties such as heat stability and shelf-life longevity, and all at relatively high dosages. These micro-encapsulated omega-3 products have greater success rates in simple food applications such as low shelf-life products (bakery and certain dairy products).
For challenging food systems, simply mixing oils or emulsions into food products isn't enough. Common reasons for the failure of encapsulated products in food applications are pH, shear and presence of minerals. Most omega-3 suppliers invest time and effort to work with the customer throughout the product-development process to overcome processing obstacles, including choosing the right antioxidants and potentially flavour-masking agents for the final product.
Along with the positive attributes expounded for the category, and omega-3s' increasing presence in the marketplace, there is confusing messaging around the health effects of the specific omega-3s, in particular the physiological significance of ALA 'vs' fish-based EPA and DHA. What many fail to understand is the critical need for both plant- and fish-based omega-3s, especially considering the increasing predominance of omega-6 fatty acids in the diet.
ALA and its counterpart omega-6 EFA, linoleic acid (LA), are converted to longer-chain fatty acids by a series of alternating desaturations and elongations. Conversion is dependent upon a number of factors. Estimates of the amount of ALA converted to EPA range from 0.2-8 per cent,1,2 with young women showing a conversion rate as high as 21 per cent.3 Conversion of ALA to DHA appears to be limited in humans, with most studies showing a conversion rate of about 0.05 per cent,4,5 although one study reported a figure of four per cent.6
ALA conversion is affected by diet, with a diet rich in LA reducing ALA conversion to EPA by as much as 40 per cent.6 The absolute amounts of ALA and LA in the diet impact conversion with significant increases in EPA synthesis, and reductions in omega-6-derived arachidonic acid (AA) synthesis noted with lower LA intakes.7 AA is the precursor of powerful eicosanoids, several of which promote the clumping (aggregation) of blood platelets, the clotting of blood within blood vessels (thrombosis), and inflammatory reactions.
Other dietary factors that interfere with ALA conversion include the intake of dietary cholesterol,8 saturated fat,9 oleic acid,10 trans fatty acids,11 alcohol12 and the ratio of polyunsaturated to saturated fats in the diet.13 High intakes of ALA, EPA and DHA can also block ALA conversion, possibly by signaling that tissue levels of omega-3 fats are adequate,14 and not (as some have claimed) that no matter how much dietary ALA is available, little will be converted.
ALA has several biologic effects, which together contribute to its positive health effects.15
ALA constitutes 75-80 per cent of the total omega-3 fatty acids in breast milk, supporting its role in the growth and development of infants.
ALA is required for maintaining the nervous system.
ALA is the precursor of EPA and DHA. ALA-rich diets increase the ALA, EPA and total omega-3 fatty acid content of cell membrane phospholipids.
ALA dampens inflammatory reactions by blocking the formation of compounds that promote inflammation, including omega-6-derived eicosanoids, cytokines, platelet activating factor and C reactive protein. Inflammation is a feature of many chronic diseases such as heart disease, type 2 diabetes, metabolic syndrome, obesity, cancer and Alzheimer's disease.16,17 Secondly, ALA interferes with the conversion of LA to AA â acting as a 'nutritional brake' to block the conversion of AA to its pro-inflammatory eicosanoids. The production of eicosanoids from AA in mononuclear cells decreased 30 per cent in healthy men who consumed flax oil for four weeks.18
Epidemiological studies and, increasingly, clinical work is supportive of a beneficial effect of ALA in minimising the risk of heart disease and for anti-inflammatory effects. ALA is the main, if not only, omega-3 in the diet of at least one billion vegetarians worldwide â despite not consuming fish, vegetarians do not have a higher prevalence of chronic diseases than nonvegetarians.
An imbalance in the n-6/n-3 ratio in tissues and blood can have adverse effects, including low-grade chronic inflammation that contributes to health problems such as atherosclerosis, Alzheimer's disease, cancer, cardiovascular disease, metabolic syndrome, obesity, osteoporosis and type 2 diabetes.22,23,24,25,26 Improving the n-6/n-3 ratio can be achieved by decreasing the intake of omega-6 fats, increasing the intake of omega-3 fats or, most importantly, doing both.
Let's be responsible and realistic
The omega-3 industry can justifiably be accused of presenting a lack of clear communication about the benefits of the family of omega-3s. For some promoting ALA, the use of 'borrowed' science from the well-studied arena of the fish-based EFAs has led to confusion and to the understandably defencive position taken by several companies marketing long-chain EFA. But some of these latter companies have gone too far in minimising the importance of ALA â even promoting the theory that because Western diets contain an abundance of the omega-6 fatty acids, the enzymes are not efficient in converting ALA, and further implying that the consumption of ALA is therefore useless. What is obvious from this somewhat convoluted logic is that we should be recommending a reduction in omega-6 fatty-acid intake. ALA will then be metabolised downstream more readily, but, more importantly, will go a long way to correcting the balance of n-6/n-3.
According to some sources, "To provide 500mg of EPA/DHA, using conversion rates of 3-10 per cent, it is estimated that a person would need to consume between 16-52g of flaxseed oil, the richest source of ALA. This amounts to a daily intake of 140-170 calories and, as such, is not a practical dietary solution." This seemingly outrageous amount of flax oil is actually only 1-3.25 tablespoons, and the caloric value is less than many protein bars on the market. To obtain a similar amount of EPA/DHA from the seed itself, larger amounts would be required and may be unrealistic, but any amount of omega-3 from flax would be of benefit â not to mention the soluble and insoluble fibres, phyto-oestrogenic compounds in the form of lignans, and an array of antioxidants that are also delivered in the seed.
No one can dispute that the current intakes of EPA and DHA in North America (130-150mg/day) are well below the levels recognised to achieve optimal health. To bridge this 'nutritional gap' will require increasing intakes of all the omega-3's - ALA, EPA and DHA, in the forms of capsules, whole-food flax and fortified foods, as well as decreasing omega-6 intakes.
EPA and DHA have been the subjects of thousands of clinical trials. In September 2004, the United States Food and Drug Administration (FDA) approved a qualified health claim (QHC) for reduced risk of coronary heart disease on conventional foods that contain EPA and DHA. This claim, however, does not extend to ALA, because ALA was not a part of the petition process. The FDA has never assessed nor denied a QHC for ALA. The flax industry, led by the Flax Council of Canada, is accumulating the data to petition the FDA for a QHC on flaxseed, as we believe that the plethora of heart-health benefits of whole flax are of great importance to the consumer and a QHC will assist in delivering this message.
Kelley Fitzpatrick, MSc, is director of health and nutrition at Flax Canada. She is a member of the Functional Ingredients editorial advisory board. Respond: [email protected]
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