Fish oils including fish liver oils for human consumption contain the highly polyunsaturated long-chain fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The levels present vary from species to species and also with geographical origin. Fish originating from South America and North Africa have higher omega-3 fatty acid content than fish caught in Northern Europe. Fish from the Southern hemisphere have more EPA than DHA. This is the opposite to genuine cod liver oil which either has a 1:1 ratio of DHA:EPA, or a slightly greater ratio in favor of DHA.
Purified omega-3 fatty acids, in particular EPA and DHA, are commonly added to a whole range of supplements including fish oils. They commonly have an unnatural and distorted EPA:DHA ratio. Purified fish oils may have a toxic effect in the body and current research is beginning to support this. These supplements are not natural. There is absolutely nothing natural about them. Increasing long-chain omega-3 intake should not involve taking “purified” omega-3 fatty acids. Instead, a person should consume more fresh oily fish and fish in general (preferably wild and not farmed).