Fish oils come from fatty fish, also known as oily fish, specifically the tissue of fatty fish, such as trout, mackerel, tuna, herring, sardines, and salmon.
Fish oils are of interest to nutritionists and health care professionals because of two main ingredients: DHA (docosahexaenoic acid), and EPA (eicosapentaenoic acid) - both types of Omega-3 fatty acids.
The fillets of oily fish contain up to 30% oil; this figure may vary. White fish, on the other hand, only contain high concentrations of oil in the liver, and have much less oil. Apart from omega-3 fatty acids, oily fish are also good sources of vitamins A and D. Whitefish also contain these nutrients, but at much lower concentrations.
Health experts commonly tell people that oily fish have more health benefits than white fish. However, their recommendations have never been compellingly proven scientifically in large population studies.
Many health authorities around the world advise people to consume either plenty of oily fish or to take supplements, because of their supposed health benefits. Studies over the last ten years have produced mixed results regarding the benefits of the dietary intake of fish oils.