Are there different forms of fish oil, and what is the difference between them?

Fish oil exists in three forms: ethyl ester (EE), triglyceride (TG), and free fatty acid (FFA). The TG form is the natural structure found in wild fish and is absorbed via the lymphatic system; the EE form is synthetic and absorbed mainly through the liver.

The most common form of fish oil on the market is the ethyl ester (EE) alcohol based form, which is a synthetic man-made form and has an alcohol metabolite “ethyl ester” backbone. The main reason most fish oil is in the EE form is that this alcohol form is easier and cheaper to produce compared to the natural form. The natural form of fish oil is triglyceride (TG), which has a glycerin backbone to which the EPA and DHA fatty acids are attached, and is how EPA and DHA come in wild fish. If the bottle doesn’t say triglyceride (TG) or re-esterified triglyceride (rTG) then it is not likely triglyceride (TG).

Companies that invest in the expensive steps required to produce a triglyceride (TG) form will always put it on the label. The triglyceride (TG) form is the main way your body transports and uses fats to help make every cell in your body. The triglyceride (TG) form increases your body’s natural absorption of the important EPA and DHA omega 3 fatty acids through the lymphatic system, while the ethyl ester (EE) form is mostly absorbed through the liver via the portal vein, which is not the natural pathway of Omega 3 absorption. Free fatty acid (FFA) form is the less common form where the glycerin backbone has been removed leaving the EPA and DHA unattached to the natural glycerin backbone. The availability of the free fatty acid (FFA) form of fish oil is limited, but research points to its absorption being similar to triglyceride (TG). The main take away from these different forms is found in this study: Bioavailability of fish oil forms