Essential Fats

Cholesterol, saturated fat and unsaturated fatty acids can all be made in the body. The fats that can’t be made in the body are Linoleic acid (omega 3) and Alpha-Linolenic acid (omega 6) and so these must be obtained from our diets. 2
The reason that our bodies cannot make these particular fats is that they are unable to manufacture the enzymes necessary to form them. The main fats that our bodies need for our cells, genes, vision and nervous system to function correctly are Arachidonic acid (AA) and Eicoapentaenoic acid (EPA). These can be formed within the body from Linoleic acid (LA) and Alpha-Linolenic acid (ALA) (See Figure 1 below). They both require the enzymes elongase and desaturase for their formation and will compete for these enzymes in the body. This is important as it means if we have too much of one type of omega in our diet this will prevent our bodies from being able to use the other type of omega.2 As the diagram shows EPA, DHA and Arachidonic acid are all obtainable from animal sources. ALA and LA obtained from plant sources are converted to GLA and EPA in the body. And GLA is further converted to Arachidonic acid and EPA converted into DHA.1  
There was a common belief that ALA could not be converted by the body into EPA.  This meant that a solely plant based diet was thought to be insufficient for obtaining adequate amounts of EPA needed for proper brain function and other processes in the body.1 There is a lot of recent research that suggests this is not in fact the case and EPA can be formed in the body from ALA.* It is however thought that in some incidences this conversion is not efficient and EPA and GLA are then considered essential nutrients. Young women are thought to have better conversion rates then young men due to estrogen levels in the body.2

In primitive diets the ratio of LA to ALA was 1:1 or 2:1. In the modern diet it is often a ratio of 10:11, 2. This is because most processed food and vegetable oils are extremely high in omega 6 while being quite low in omega 3. It is often recommended that the majority of people should aim to reduce their omega 6 intake. In the post Diet Analysis it shows where omega 3 and 6 are taken in in the diet and how a correct ratio can be achieved.
To ensure adequate intakes of omega 3 and 6 it can be recommended to take a mixture of seeds each morning. To get a good quantity of omega 3 a heaped tablespoon of ground and soaked flaxseed can be taken each day. Alongside that 1 teaspoon each of two of the three seeds: sunflower, pumpkin and sesame seeds can be taken. See Figure 2 (below). This should provide a good ratio of omega 3 to 6. To complete the balance one small handful of soaked nuts (almonds, hazelnuts etc) can also be included daily.

If processed foods, soya products and walnuts are included on a daily basis there may be no need to add sesame, sunflower and almonds to the diet in order to get sufficient omega 6. In fact it may be best to refrain from eating such foods as they may upset the omega 3, 6 balance.
As already mentioned the ratio of linoleic (omega 6) to alpha-linolenic acid (omega 3) is extremely important for the correct absorption of both. There are many variations in the recommended omega 3 and 6 ratios. This is because while an increase in one can show positive effects in the body (ie a reduction in blood chlosterol) by affecting the uptake of the other detrimental effects may also occur. A particular balance of the two needs to be met in order for EPA and DHA amounts to be of an appropriate level in the body.
By comparing the different recommendations and choosing a ratio that’s somewhere in the middle we are left with a ratio of 1:3 1  It would not be recommended to have any more omega 6 as this would reduce the amount omega 3 available to the body. In terms of total daily calories this could be expressed as: ALA (omega 3) 1-2% and LA (omega 6) 4-6%

*One of the main studies that showed that ALNA had a limited ability to convert into EPA is thought to be incorrect in its measurement of ALNA in the test subjects. ALNA is stored in the liver and released over a period of weeks. It was assumed in the experiment that when ALNA levels were found to be low in the plasma that was an indication that ALNA was not present in the body. However as ALNA is stored in the liver, this assumption was incorrect.1

[1] Walsh, S. Reprinted 2012, Plant Based Nutrition and Health, The Vegan Society, Birmingham
[2] Higdon, J. 2005, Essential Fats, The Linus Pauling Institute Micronutrient Information Center [Online] Available at: Accessed 13/9/13

Additional Note
In Patrick Holefords book ‘The Optimum Nutrition Bible’ he recommends getting 3.5% of daily calories from omega 6 (linolenic acid) and 3.5% from omega 3. He achieves this ratio though a suggested intake of seeds as shown in figure 2 below, providing a ratio of approximately 1:1. However, this recommendation does not take into consideration the great amount of omega 6 that most diets contain without any seeds being consumed.