Exploring Plant-Based Omega-3 Sources
Tuesday, September 12th, 2017 | 258 Views
The term ‘omega-3’ usually first brings fish oils to mind, but there are also plant-based sources such as linseed or chia seed. These offer a more sustainable source while providing comparable health benefits. By Lindsay Brown, professor (biomedical sciences), university of Southern Queensland
Fats are an important part of the human diet as they provide energy and allow fat-soluble vitamins to be absorbed. Fats provide about twice the number of calories per gram as carbohydrates and proteins.
Dietary fats are taken up by fat cells, particularly in the abdomen, for use as energy stores for the body for activities between intermittent food consumption. During exercise, carbohydrates are used first, followed by fats when exercise is prolonged.
Individual fats are described by their chemical structure as either saturated (no double bonds), monounsaturated (one double bond) or polyunsaturated (two or more double bonds).
Common sources of saturated fats are animal fats; olive oil is a common source of monounsaturated fats; while polyunsaturated fats come from dietary oils such as peanut or canola oil, and fish oils.
Analysing Fatty Acids
Polyunsaturated fats (or fatty acids) are separated based on their chemical structure into omega-6 fatty acids (as in most plant-derived oils) and omega-3 fatty acids (such as in fish oils, linseed and chia oils).
To the average consumer, they perceive saturated fats as unhealthy, while unsaturated fats (both monounsaturated and polyunsaturated) are considered as healthy, but this definition is an over-simplification.
Ancient human diets probably contained approximately equal amounts of omega-3 and omega-6 fatty acids; in contrast, modern westernised diets contain at least 10 times more omega-6 fats (with figures going up to even 30 times more) than omega-3 fats.
This dietary change may underlie the increased incidence of chronic diseases such as obesity, diabetes, cardiovascular and renal diseases as well as inflammatory diseases including arthritis. The three most prevalent omega-3 fatty acids in the diet are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). ALA is primarily produced from plants, especially linseed (flax) and chia. In contrast, EPA and DHA, referred to as long chain omega-3 fatty acids, are produced by algae and then concentrated in fish, especially oily fish, which eat these algae.
EPA and DHA, rather than ALA, have been the focus of research on omega-3 fatty acids, probably due to the relatively inefficient conversion of ALA to EPA and DHA in rodents and humans.
The widespread assumption is that DHA mediates most biological actions of the omega-3 fatty acids, yet almost all studies have used a mixture of EPA and DHA, rather than purified fatty acids. This also assumes that ALA is inactive and must firstly be metabolised to longer chain compounds, especially DHA, to produce biological responses.
There are remarkably few studies comparing these three omega-3 fatty acids as individual compounds in preventing or treating chronic disease states. However, there is increasing evidence that ALA produces different effects from DHA by activating different receptors so that the mechanisms of action differ, with anti-obesity effects predominating for ALA and anti-inflammatory effects for DHA.
Health Benefits Of Fish Oils
Possibly the most studied dietary intervention in the prevention or treatment of disease is the Mediterranean diet, consisting of fish, unsaturated fats, whole grains, fruits and vegetables, nuts and legumes, with moderate ethanol consumption. Clinical trials starting with the Seven Countries Study in the 1980’s have shown that this lifestyle decreased the risk of many diseases including cardiovascular disease, breast cancer, depression, colorectal cancer, diabetes, obesity, asthma, erectile dysfunction and cognitive decline.
However, are these responses due to the omega-3 fatty acids, or the combination of many compounds from this complex diet?
The Heart Foundation has recommended that to lower the risk of coronary heart disease, individuals should consume about 500 mg per day of combined DHA and EPA through a combination of either two or three servings (150 g per serving) of oily fish per week, fish oil capsules or liquid, or food and drinks enriched with marine omega-3 fatty acids.
They also recommended the consumption of at least 2 g per day of ALA, but few studies have tested the cardioprotection of chronic intervention with ALA. Many clinical trials have now been published, mostly using marine omega-3 fatty acids, on non-cardiovascular diseases including cancers and psychiatric disorders.
Many patients benefit from chronic supplementation with the marine omega-3 fatty acids, but the mechanisms of action of these fatty acids are complex and controversial.
Linseed And Chia Seed
With the extensive research done on marine-based omega-3 fatty acids, much is already known about their benefits. However, what about plant-based sources?
Ancient grains such as linseed and chia seed can also provide a substantial amount of omega-3 fatty acids, and with better results.
Domestication of linseed occurred in the Middle East, probably around 8,000 years ago, so it is truly an “ancient grain”. It has been used to make linen for cloth, but also for medicinal purposes in both ancient and modern societies.
Canada is the world’s largest producers of linseed with production in 2013 amounting to 712,000 tons (around 32 percent of the world’s production of 2.2 million tons at that time); other countries producing more than 100,000 tons in 2013 included China, Russia, Kazakhstan, India and Ethiopia.
Chia is also referred to as an “ancient grain”, originating in the central valley of Mexico and a widely used grain in the Aztec civilisation. World production in 2013 was estimated as 15,000-30,000 tons with US demand around 7,000 tons. Chia grows in a relatively restricted zone around 15 degrees from the equator, with Mexico, Bolivia and Argentina as the major producers in Latin America.
Linseed and chia seeds both contain about 20 percent ALA but the advertised retail prices can be very different—chia seeds can cost as much as three times the price of linseed.
Sustainability Of Omega-3 Sources
An important argument in favour of plant-derived omega-3 fatty acids is the sustainability of production, in contrast to fish oils. Numbers of wild fish have decreased markedly over the last 50 years, in some cases to around 10 percent. Over the same period, fish farming has increased with claims that around 50 percent of all fish were produced by aquaculture in 2016.
In aquaculture, fish are fed with fish meal and fish oil, with the United Nations’ Food and Agriculture Organisation (FAO) estimating that 81 percent of the world’s fish oil production was used in aquaculture in 2009 with a retention rate of 40-50 percent in the farmed fish.
Fish meal can be replaced by terrestrial oilseeds to maintain growth, but this decreases omega-3 fatty acid content so that twice the Atlantic salmon intake from farmed fish was required in 2015 compared with 2006 to satisfy recommended nutritional intake. Further, farmed fish which were fed terrestrial oilseeds were found to have higher contents of omega-6 fatty acids and saturated fatty acids— worsening the omega-6 to omega-3 ratio in the human diet.
These problems are not applicable to the production of plant-derived ALA. Sustainable and cost-effective sources of EPA and DHA will need to be found to allow aquaculture to provide adequate dietary intake of these omega-3 fatty acids. Fish as a source of long-chain omega-3 fatty acids could be replaced by genetically-engineered plants, both for human health and aquaculture, as these plants have been shown to produce similar amounts of these fatty acids as in fish oil. This option may meet considerable consumer resistance.
Health Benefits Of Linseed In The Diet
On top of offering a sustainable source of fatty acids, plant-based sources such as linseed can also offer several health benefits. It must be noted that to date very few studies have reported trials in humans testing the health benefits of linseed containing ALA as well as lignans (estrogen-like chemicals which act like antioxidants) and fibre.
Dietary intervention with 30 g milled flaxseed (linseed) was administered for six months to 58 patients with peripheral artery disease and an average systolic blood pressure of about 142 mmHg and diastolic blood pressure of about 77 mmHg. Results showed a lowering of systolic blood pressure by about 10 mmHg and diastolic blood pressure by about 7 mmHg.
These effects were selective to hypertensive patients, and long-lasting. In patients with mild hypertension, responses were very similar to what was expected with optimal antihypertensive drug treatment.
Further studies from the same group also showed that ALA in flaxseed may have inhibited soluble epoxide hydrolase, decreasing oxylipins (oxygenated natural products) derived from polyunsaturated fatty acids, which therefore triggered the abovementioned antihypertensive responses. Further, flaxseed independently lowered plasma cholesterol concentrations in these patients.
These exciting results show that linseed can be used as a nutritional strategy to deliver desired results in a relatively inexpensive manner. Further clinical trials are still warranted however, for example on heart failure and cancer patients, so as to compare the effectiveness of ALA with fish oils.
The sustainability of ALA production from land-based plants, combined with effective reduction of blood pressure and cholesterol concentrations, makes intervention with ALA into an important and realistic public health initiative.
Increasing Linseed And Chia In The Diet
Linseeds can be incorporated in foods usually as whole seeds, for example in bread, or as milled flax to be baked in muffins. In a study, both milled linseed and that oil-baked into muffins showed increased blood ALA concentrations, while whole linseeds did not, with the whole seeds causing gastrointestinal distress and reducing compliance in patients.
As such, the FlaxPAD trials developed a range of products to provide milled linseed at a dose of 30g/day, including bagels, muffins, bars, buns, pasta, tea biscuits, and even in yoghurt. With regard to taste, taste testing in the trials showed that cinnamon raisin was a promising flavouring alternative in ALA bagels.
The internet is a wonderful source of home recipes for both linseed and chia seeds, too many to mention here. The range is enormous, so there is sure to be a favourite recipe just waiting out there for everyone!
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