Fatty acids can be divided into saturated and unsaturated fats based on their molecular composition.
Saturated fatty acids (SFA) are made by the body and are not required in the diet. They have no double bonds. In excess amounts, saturated fats can increase the amount of cholesterol in your blood, which can increase the risk of developing a disease. It's good to keep your intake of saturated fats as low as possible although due to that food containing healthy fats also contain saturated fat this is difficult.
Unsaturated fatty acids are further classified as either monounsaturated or polyunsaturated fats based on the number of molecular bonds they obtain. Monounsaturated fats (MUFA) have one double bond whilst polyunsaturated fatty acids (PUFA) have two/more double bonds . The double bonds may be either of cis or trans configuration.
Trans fats come mainly from fats that have been hydrogenated. They acan cause serious damage in cell metabolism and also lead to immune system depression, cardiovascular disease, diabetes, obesity, sterility, birth defects, decreased ability to produce breast milk, loss of vision, and weakening of your bones and muscles. Almost all polyunsaturated fatty acids found in nature are thankfully of the cis configuration.
There are three major types of unsaturated fatty acids: omega-3, omega-6 and omega-9. The omega-6s and omega-3s are the essential fatty acids (EFA's). The omega-9s are non-essential because the body can make them from other fatty acids.
Essential Fatty Acids (EFA's)
Omega-6s and omega-3s are considered to be essential due to that your body cannot make them and therefore they must be obtained through your diet. Your EFA's include:
Omega-6 fatty acid: 'linoleic acid' (LA)
- Derivatives: Gamma-linolenic acid (GLA) & arachidonic acid (AA) (Generally considered essential)
Omega-3 fatty acid: 'alpha-linolenic acid' (ALA)
- Derivatives: Eicosapentaenoic acid (EPA) & docosahexaenoic acid (DHA). (Generally considered essential)
One of the essential keys to optimal health is to maintain a good balance between these polysaturated fatty acids. You can achieve a good balance by eating a balanced diet abundant in vegetables and a less significant amount of fruits, legumes, nuts, seeds, whole grains as well as cold-water fish (or fish oil capsules if you don't eat fish). 
Polyunsaturated fatty acids can become harmful to human health when heat exposed due to formation of free radicals. [2,3, 4]
What does EFA's do?
EFAs are needed for the structure and function of every cell in the body, they are vital for our health. EFAs increase the absorption of vitamins and minerals, they nourish the skin, hair and nails, they promote nerve function; assist in producing hormones; ensure normal growth and development and prevent/ treat disease.
EFA deficiency is common because of dietary and lifestyle choices. People also lack ability to properly turn LA and ALA to their derivatives.
What Foods contain EFA's?
Omega-6 (LA): Vegetables & most vegetable oils – sunflower (65-75%), safflower (79%), evening primrose seed (72%), corn (57%), peanut (31%), canola (19-26%), and olive (8%).
Omega 6 Derivative (GLA): Borage oil (starflower),GLA (20-24%); evening primrose oil (8-10%); and black currant oil (15-17%). GLA isalso present in small amounts in human breast milk and some foods. A normal human diet contain very little GLA.
Omega 6 Derivative (AA): Eggs, fish and meat
Omega-3 (ALA): ALA is found in flax seed (18-22%) and flax seed oil (50-60%), and in small amounts in some nuts, green leafy vegetables, canola, wheat germ and black current seeds.
Omega-3 Derivatives (EPA and DHA): Fatty fish (salmon, mackerel and tuna), fish oils vary in the amount of EPA and DHA they provide.
All users are urged to always seek advice from a registered health care professional for diagnosis and answers to their medical and nutritional questions and before making changes in their diet or training.