The best form of cod liver oil is triglycerides. Triglycerides are the form that omega-3 oils are naturally found in nature, including our body and cod livers. However, most cod liver oil manufacturers will convert triglycerides into ethyl esters during processing. This makes the oils much easier to isolate, filter out and concentrate. As ethyl esters are not natural, it is widely thought that they are not absorbed or utilised by the body as well.
Some brands, such as Carlson’s Labs convert their ethyl esters back into triglycerides after filtering and extraction has been done. In theory, this would make their oil comparable to the brands above.
It is often difficult to tell if a cod liver oil brand contains ethyl esters or triglycerides, and it is almost never included on their bottle. Generally speaking, high street brands – those found in pharmacies, supermarkets and health food shops, will contain ethyl esters, whereas the niche and specialised brands like those mentioned above will contain triglycerides.
If you are in doubt it is always worth contacting the manufacturer for more information on their product. Their response should give you a good idea of the quality of the product, and they should tell you what form the oil is in. To illustrate the variation in the quality of different cod liver oils we have compiled a ‘fish oil showdown‘, which compares high quality cod liver oils with lower quality ones, the form of the oils, the form of the vitamins and how the oils are processed.