The essential fatty acids can be divided into two main groups: omega-3 and omega-6. These are called essential because they must be taken in through food, the body can not create them on its own. It is therefore essential that they are included in the food.

Omega-3 fatty acids are polyunsaturated and can be short-chain or long-chain omega-3. ALA (alpha linolenic acid) is a short-chain fatty acid consisting of 18 carbon atoms and derived from plants. Walnuts, rapeseed oil and flaxseed oil are rich sources of ALA. The long-chain fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) come mainly from animals, and consist of 20 and 22 carbon atoms. These are mostly found in food from the ocean, such as oily fish.

It is really only alpha linolenic acid (omega-3) and linoleic acid (omega-6) that are essential, since the body can create the other fatty acids from these two. A good balance between omega-3 and omega-6 is needed for optimal health. It is therefore important to eat fish or fish oil supplements that are rich in EPA and DHA. The body and brain need fish oil to neutralize the damaging effects that too much omega-6 can have on the body, something that can lead to inflammation and disease. Unfortunately, many people do not eat enough fish or fish oil, instead they eat too much omega-6 in relation to omega-3. Omega-6 is found in meat, sunflower oil and soybean oil.

The omega-3 fatty acids are polyunsaturated which means that they have two or more double bonds in the carbon chain. Double bonds are instabile and the oil therefore easily goes rancid (oxidates). It is also heat-sensitive. When the oil oxidates free radicals are created, that attack the cells in the body. Eating oxidated oil is therefore not healthy. Antioxidants protect the oil from oxidation, both inside and outside the body. There are lots of antioxidants in fruits, vegetables and tea. The polyunsaturated fatty acids are also used to create eicosanoids which are important hormones in the body.

The cell membranes contain lots of omega-3s, and these fats influence the cell's function. If there is a deficiency of these fatty acids, the cells will use other types of fat instead, e.g. saturated fat. The consequence is that the cell membranes will not work optimally and they become less adaptable and less flexible.

DHA is short for docosahexaenoic acid and it can also be written as 22:6n-3. This means that DHA has 22 carbon atoms with 6 double bonds, and n-3 is short for omega-3. The 3 means that the first double bond is between carbon atom 3 and 4. DHA is needed for the brain and eyes, and if fetus does not receive enough DHA it can impair eye and brain function. Half of the fat in the brain's cell membranes is DHA, with a concentration in celebral cortex, synapses and mitochondria, which are all very important parts of the brain. Therefore DHA is critical for the brain to work optimally.

EPA is short for eicosapentaenoic acid and can also be written as 20:5n-3. It means that EPA has 20 carbon atoms with 5 double bonds. N-3 means that it is an omega-3 fatty acid. EPA is, just like DHA, important for the brain and the cells in the body. Researcher Andrew Stoll writes that EPA appears to be the fatty acid that regulates mood. Furthermore, the body needs EPA to create good eicosanoids. EPA is also anti-inflammatory.

ALA is short for alpha linolenic acid. It is a short-chain fatty acid consisting of 18 carbon atoms and 3 double bonds (18:3n-3). ALA is the mother of the omega-3s and is found in linseed/flaxseed oil, rapeseed oil, green leafy vegetables, and walnuts. Side effects: a very high intake of ALA can lead to mania for patients with bipolar disorder, writes researcher Andrew Stoll. Be also aware that flaxseeds - not oil - contain cyanogenic nitrates which is toxic in high doses. Stoll writes that you should not eat more that 2-3 tablespoons per day. In Sweden it is recommended not to eat more than 1-2 tablespoons per day of flaxseeds.

It is not known whether ALA is good for health in itself, or only through its long-chain derivatives EPA and DHA. The transformation in the body has shown different results in studies. However, it seems that the transformation is often inefficient. A number of factors appears to be limiting the transformation, such as the amount of EPA and DHA already in the body, age, gender, genes and other physical prerequisities. It seems as though the body can transform more of it when it is needed, such as stress and pregnancy, writes reseacher Edward Emken in an article. A study (Pawlosky et al.) from 2001 showed that a very small amount of ALA was transformed to EPA, only 0.2 percent. The further transformation to DHA was much more efficient. The researchers say that you should not exclude EPA and DHA from your diet.