Fish Oil Triglycerides vs Ethyl Esters

From my experience as a retail pharmacist, fish oil is one of the most sought after item. Do you know that the product that you buy might not be of pharmaceutical quality. Although a product label may say “Fish Oil”, the chances are the product is not an oil at all, rather it is an alternate lipid class called a fatty acid ethyl ester (FAEE) or just EE for short. The authentic fish oil has a chemical structure known as a triglyceride (TG).

This post is to help our reader to differentiate between ethyl ester and triglyceride fish oil.

What are triglycerides (TG)?

The National Academy of Sciences defines fats and oils as “complex organic molecules that are formed by combining three fatty acids with one molecule of glycerol”. Triglycerides contain three fatty acids (i.e. EPA and DHA) esterified (bonded) to a glycerol backbone. TGs are the natural molecular form that make up virtually all fats and oils in both animal and plants species. The omega-3 fats present in fish are almost exclusively TGs. Free fatty acids are rapidly oxidized. Therefore, TG structure offers greater stability to the fatty acids and prevents breakdown and oxidation.

What are ethyl esters (EE)?

Fatty acid ethyl esters are a class of lipids that are derived by reacting free fatty acids with ethanol (alcohol). This process is known as trans-esterification. The industry make of use this EE form, as they can use fractional distilation (molecular distilation) to selectively concentrate EPA and DHA to levels greater than found naturally in fish. 

This EE form of fish oil is wrongly markets as fish oil..

Are all fish oil concentrates ethyl esters?

Majority of fish oil concentrates sold globally are EPA and DHA EE concentrates. A small percentage of fish oil concentrates on the market are natural TGs.

It is possible to convert the fatty acids back to TGs using food grade enzymes, through a process called glycerolysis. However, it will easily add 30-40% to the final product cost.

Is there any difference in the absorption and metabolism of natural triglycerides vs. ethyl esters

To make it simple, just remember that fish oil need to be digested by pancreatic lipase enzyme. EE form will be different, because its fatty acid-ethanol bond is 50 times more resistant to pancreatic lipase enzyme. 

Another thing is EE form need to be reconverted back to TG form before tranported in the blod. TG resynthesis will be delayed without any free glycerol in the body. This delay could cause an increase in free fatty acids and subsequent oxidation of those free fatty acids

There are many studies that favour both TG and EE form, but the overall evidence suggests that TG fish oils are better absorbed in comparison to EE. Natural TG fish oil results in 50 % more plasma EPA and DHA after absorption in comparison to EE oils. One of the factors for the poor bioavailability of EE is a much greater resistance to digestive enzymes.

How about other countries?

Some countries (e.g. Australia) have gone as far as banning the sale of EEs. Other countries such as the US, Canada, and the UK allow the sale of the EE form and furthermore do not require any additionally labeling. These supplements are therefore often incorrectly labeled as “Fish Oil” and pose a risk to those who must avoid ingestion of alcohol.