By Hazel Grassie
Sources of unsaturated fats (source: http://goo.gl/k5z22F)
The “Essentiality” of Omega Fats
In Part 1, I described how unsaturated fats not only support bodily processes, but also have extra health benefits. Monounsaturated fats in plant oils, nuts and seeds feature heavily in the cardiac friendly Mediterranean diet, particularly Omega 9. Polyunsaturated fats (PUFAs) comprise of Omega 3 and Omega 6, alpha linolenic acid (ALA) and linoleic acid (LA) respectively. Using substrates within the body, humans can synthesize some fatty acids. However, it cannot introduce double bonds in the location necessary to make Omega 3 and 6. As insufficient levels causes deficiency symptoms, omegas 3 and 6 are deemed ‘essential’ and they must be consumed preformed in the diet. Once in the body, these PUFAs can be lengthened to create long chain polyunsaturated fatty acids (LC-PUFAs). Omega 3 (ALA) is elongated into Eicosapentaenoic acid (EPA) and Docosahexaenoic acid (DHA) and Omega 6 is elongated to Aracidonic acid (AA).
The Action of Omega 6 LC-PUFAs
Dietary sources of Omega 6 fats include most vegetable oils (amongst others; safflower, sunflower, grapeseed, corn, cottonseed and soybean), avocado, poultry and dairy products. Omega 6 (LA) maintains the skins integrity by blocking out harmful substances and preventing excessive water loss. This is evidenced by the appearance of eczema in times of deficiency. Furthermore, LA is the only precursor molecule to AA, an Omega 6 LC-PUFA. AA is found in all human cell membranes, particularly condensed in brain cells and blood vessels. We could consider AA as a command molecule, as its release from cell membranes triggers bodily signaling processes, like blood clotting and immune and hormonal responses. Unfortunately, in excessive amounts (as are consumed in western diets), AA plays a role in inflammatory conditions like asthma and arthritis. In fact, the action of pain relief and anti-inflammatory medications target AA derivatives. AA is also responsible for clot formation involved in strokes and heart attacks. Furthermore, some research indicates that AA can encourage the growth of tumour cells. However, we must remember that AA is crucial to human health, despite its involvement in health conditions when consumed in excessive amounts.
The Functions of Omega 3 LC-PUFAs
The best dietary sources of omega 3 (ALA) fats include oily fish (salmon, mackerel, anchovies, sardines, herring and trout), walnuts, flaxseeds and eggs. Omega 3 fats are converted to LC-PUFAs; DHA and EPA in the body, which both have differing health attributes. Like AA, DHA is found in human cell membranes. DHA levels are condensed in brain, heart and retina cells indicating its key functionalities. Unlike AA, DHA levels in the brain fluctuate in accordance with dietary intake of Omega 3. The brain has a preference for DHA uptake over other fats, suggesting that dietary Omega 3 is greatly involved in brain function. Indeed, it plays a crucial role in the development of the fetal brain and the prevention of cognitive decline. DHA sufficiency is associated with learning ability, whilst insufficiency is related to learning deficit. Furthermore, long-term studies show that consumption of 200mg DHA from oily fish is associated with a 50% reduced chance of heart attack, one of the leading causes of death in first world countries.
EPA also has specific actions in health. Important anti-inflammatory hormones, know as Eicosanoids are derived from EPA. Thus, EPA is efficacious in the prevention of inflammatory conditions like cardiovascular disease (CVD) and arthritis. Scientific research shows that lower blood levels of EPA and DHA are related to greater CVD risk. EPA also plays a role in mental health, whereby conditions like depression and ADD respond well to EPA supplementation. A meta-analysis of depression patients showed that those taking a supplement with a high EPA: DHA ratio had fewer depressive symptoms. Oily fish do not naturally produce EPA. They consume it from algae thus; commercially available microalgae is a great vegetarian source of EPA.
The Important Omega3/Omega 6 Ratio
The body takes Omega 3 and 6 PUFAs and makes them longer to create LC-PUFAs that have the health benefits described above. This processes requires the enzymes Desaturase, which adds double bonds, and Elongase, which adds carbon molecules to the chain. Both Omega 3 and 6 must share what is available of these enzymes. If we consume more Omega 6, we will ultimately synthesize more AA. Conversely, if we consume greater quantities of Omega 3, we will synthesis more EPA and DHA.
Currently, in western diets the ratio of dietary Omega 6 to Omega 3 is 17/1. This high ratio may promote the occurrence of common diseases including CVD, cancer and arthritis. Scientific trials have shown that reducing this ratio by increasing Omega 3 PUFA has suppressive and therapeutic effects. For example, reducing the ratio to 4/1 was associated with a 70% decrease in total mortality from CVD in secondary prevention CVD patients. A ratio of 2.5/1 reduced rectal cell growth in patients with colorectal cancer. Furthermore, a ratio of 2-3/1 suppressed inflammation in patients with rheumatoid arthritis and asthma. These studies indicate that the optimal ratio may vary, with the disease under consideration due to the multifactorial nature of different diseases. Thus, the optimal therapeutic ratio may depend on the disease in question and its severity.
In western diets we consume more Omega 6 than Omega 3. This comes from plant oils like sunflower, corn and soybean, as well as nuts and seeds. Omega 3 sources like oily fish, walnuts and linseed are unfortunately consumed to a much lesser extent. The dietary requirement for Omega 6 (LA) is 3-4 grams per day. On average the western diet contains up to 18g per day. As western diets are high in Omega 6, AA supplies are sufficient. The current intake of the Omega 3 LC-PUFAs is less than 100 mg per day in many western countries. For better heart health some researchers advise that we consume 1-2g of LC-PUFAs (Omega 3 EPA and DHA) per day. Lowering the intake of Omega-6s would reduce the amount of Omega-3 LC-PUFAs needed to obtain their health benefits, without compromising the benefits of Omega-6 LC-PUFA.
Omega 3/6 balance comparison (source: http://anyhooo.net/tag/omega-3/)
In summary, a lower ratio of Omega-6/Omega-3 fatty acids is more desirable in reducing the risk of common chronic diseases in developed societies. Based on the evidence to date, my advice is to increase consumption of Omega 3 fat sources. Chose oils rich in monounsaturated fats like olive and canola, whilst using Omega 6 oils (particularly sunflower and safflower) sparingly. Unfortunately, most people do not eat enough whole fish. However, increasing awareness of the health benefits of Omega 3 fats in particular has caused sales of fish oil supplements to surge over recent years. In my upcoming article, I will be making an all round comparison of whole oily fish and fish oil supplements to investigate your best route to increasing LC-PUFAs.