There are two types of Poly-Unsaturated Fatty Acids (PUFA): Omega-3 and Omega-6. Omega-3 fatty acids play a crucial role in lowering blood pressure, reducing bad cholesterol levels, reducing inflammation, stimulating healthy hair growth and have even been showed to correlate with memory, intelligence and other brain functions. There are a number of different types of Omega-3 fatty acids which differ in the chemical structure but the three most important are eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and alpha-linolenic acid (ALA). Foods that are high in Omega-3 include oily fish (like sardines, mackerel, tuna, salmon, swordfish), fish oil supplements, flaxseeds, chia seeds and walnuts.
Omega-6 fatty acids are the other type of PUFA and mainly consists of something called linoleic acid. Omega-6 can help reduce heart disease and decrease bad cholesterol however if consumed in excess it can actually cause inflammation and other associated issues like rheumatoid arthritis, heart disease and hormonal problems. Foods that are high in Omega-6 include refined vegetable oils and foods that are cooked and prepared in vegetable oils (such as French Fries, popcorn chicken, dairy and eggs, cookies, muffins and bread).
They key to getting the right quantities for Omega-3 and Omega-6 in your diet is with getting the ratio between them correct. Both Omega-3 and Omega-6 are broken down along the same enzymatic pathway and therefore compete with each other to be digested so if you eat too much Omega-6 then this will be broken down ahead of Omega-3. This in turn leads to an excess Omega-6 and associated issues like inflammation caused by too much linoleic acid. The recommended ratio of Omega-3 to Omega-6 fatty acids in your diet is one to four however most people tend to eat far more Omega-6 because of its prevalence in the cooking oil of popular foods like burgers, French Fries, potato chips, cookies and muffins (in fact, a typical Western diet has an Omega-3 to 6 ratio of between 1:10 and 1:50).
To combat this problem, you should try to increase your Omega-3 intake to improve the ratio. There are no daily recommendations for your Omega-3 intake however a good target is around 1,100 mg per day as a woman and 1,500 mg per day as a man. If you are at risk from heart disease, mood disorders or cancer then you can increase your dosage of Omega-3 anywhere up to 4,000 mg per day (there is a list of foods which are high in Omega-3 can be found in Appendix 2). It can often be hard to get the Omega-3 content of foods so as a rule of thumb, you should aim to eat oily fish twice a week.
Finally, you may have heard of Omega-9. Omega-9 is actually a MUFA and therefore not an essential fatty acid. It is found in most of the cells in the body and plays an important role in blood and hormonal functioning. Omega-9 is commonly found in oils and nuts and so you do not need to think too much about it.
 Be mindful that certain types of fish are more susceptible to the bioaccumulation of mercury. Mercury is a naturally occurring heavy metal which can bio-accumulate in fish in the form of methylmercury, which is highly toxic. Larger and longer-living fish tend to contain the most mercury such as shark, swordfish, fresh tuna, marlin, king mackerel, tilefish and northern pike. Try to choose lower-mercury fish and seafood, such as salmon, shrimp, cod, and sardines.