Food and Behaviour Research

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Dietary Sources of Omega-3 Fatty Acids

Date: 2015

Modern diets are often low in omega 3 fatty acids

  • Our diet has been constantly changing over the centuries and so have our dietary sources of fatty acids. Research indicates that the diet of our ‘hunter-gatherer’ ancestors was relatively low in saturated fat but contained special kinds of polyunsaturated fats (omega-3 and omega-6) that are crucial to brain development and function. The ratio of omega-6 to omega-3 in the diet at that time is thought to have been between 1:1 and 4:1, and our physiology has not changed significantly since then.
  • In contrast, modern diets are often high in saturated fat and trans fats (artificially saturated fats found in many processed foods), and they particularly lack omega-3 fatty acids. The current dietary ratio of omega-6 to omega-3 fats ranges from 14:1 to about 20:1 in the western world.
Why a lack of long-chain omega 3 fatty acids in the diet matters
  • This relative deficiency of omega-3 fatty acids (and the high level of saturated and trans fats) has been linked with many physical health problems, including heart disease and stroke, cancer, inflammatory conditions and auto-immune diseases.
  • During pregnancy and infancy, a good supply of long-chain omega-3 (known as EPA and DHA) are needed for healthy brain development and function. Other things being equal, higher intakes of fish and seafood by mothers during pregnancy are associated with better verbal intelligence and other developmental outcomes in their children (see Hibbeln et al 2007)
  • A relative lack of long-chain omega-3 in the diet is associated with child behaviour and learning problems such as ADHD, dyslexia, dyspraxia and autistic spectrum disorders. Controlled trials show that increasing dietary intakes of these special fats can improve behaviour and learning - both in children formally diagnosed with these conditions (Richardson and Montgomery 2005Bloch and Qawasmi 2011), and in children from the general school population. (Richardson et al 2012)
  • Research also shows that a lack of omega-3 may increase the risk of depression and other mental health conditions. Based on the evidence from controlled clinical trials, the American Psychiatric Association recommends long-chain omega-3 as an add-on treatment for clinical depression (at a dose of at least 1000mg of EPA + DHA, equivalent to around 4 good portions of fish and seafood per week) (see Freeman et al 2006)
  • Because omega-3 fatty acids are so important for both physical and mental health, current advice from UK and US governments is that we should try to increase our intake of omega-3 fatty acids (and reduce our intake of trans fats).

Only fish and seafood provide the complex omega-3 most important to the brain

  • The two most important omega-3 fatty acids for brain function and brain development are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These can be found directly only in fish and seafood. Oily fish contains more EPA and DHA than white fish. Sardines and pilchards, anchovies, mackerel, salmon and herring are particularly good sources.
  • The UK Food Standards Agency recommends that we eat at least two portions of fish per week (one of which should be oily fish). This would provide around 1-2 grams of EPA and DHA combined. However some people may benefit from a much higher intake of these complex omega-3, as suggested by treatment studies in physical conditions such as arthritis, or psychological conditions such as depression or schizophrenia.  They have also been found to be helpful in specific learning difficulties, including dyslexia, dyspraxia and ADHD.

Some vegetarian foods contain simpler omega-3 fats - but conversion to EPA and DHA is not reliable in humans

  • Vegetarians, who do not eat fish, have no direct source of EPA and DHA in their diet, so they rely on the body converting a simpler omega-3 fatty acid, alpha-linolenic acid (ALA), into EPA and DHA. ALA is found in green vegetables and some nuts and seeds (such as walnuts, brazil nuts and flaxseed), although the best concentrated source is flaxseed (linseed) oil.
  • Although some people may be able to obtain enough EPA and DHA without consuming fish or seafood, evidence shows that most people cannot - particularly if they are consuming a modern. western-type diet rich in omega-6 fats.
  • This is because the conversion process for making long-chain omega-3 fats from ALA is not efficient. Studies show that on average, less than 5% of dietary ALA is converted to EPA, and less than 1% becomes DHA.  For this reason, DHA is regarded as a dietary essential according to a consensus of the world's leading independent scientists. (Brenna et al 2009)
  • An excess of short-chain omega-6 from vegetable oils (found in most processed foods) is thought to be the main reason for the poor conversion of short-chain omega-3 from plant sources (ALA) into the omega-3 the brain needs (EPA and DHA).  
  • Poor conversion of short- to long-chain omega-3 may also occur owing to other diet and lifestyle factors, or for constitutional reasons. For example, low levels of certain vitamins and minerals, or high stress levels, can impair this process, and it also appears to be less efficient in males than females. Conversion is also limited in young infants and in the elderly, but individual genetic  differences in fatty acid metabolism can impair some people’s ability to make sufficient EPA and DHA from ALA at any age.
  • The long-chain omega-3 (DHA, and to a lesser extent EPA) can be derived from some special forms of algae - and these vegetarian forms are now available from supplements or fortified foods. These are the best dietary sources of omega-3 for vegetarians, vegans and others unwilling or unable to eat fish and seafood, or to take supplements of oils from seafood sources.