Why Choose a Triglyceride Fish Oil Instead of Ethyl Ester Fish Oil

By Henry Lau

Fish oil is typically sold in three forms: ethyl ester, natural triglyceride, and re-esterified triglyceride. Though taking any kind of fish oil is better than not taking it at all, the majority of research finds triglyceride forms being superior over ethyl ester in terms of stability and absorption — that’s why we sell it.

Which Form is Better?

There are 3 qualities to consider when looking at what type of fish oil form you are buying: low levels of contaminants, high bioavailability, and shelf life stability.

Natural Triglyceride Form:  This form of fish oil has high bioavailability but also has higher levels of contaminants because it is not purified. This form is also lower in EPA and DHA because it is not concentrated.

Ethyl Ester Form: This form of fish oil is converted from its natural triglyceride form into synthetic ethyl ester to remove heavy metals and other impurities; this type of fat does not exist naturally. An ethyl ester is made by removing the glycerol backbone of the fatty acid and replacing it with an ethanol molecule. In this stage, the fish oil is concentrated into higher levels of EPA and DHA. However, though an ethyl ester fish oil product may be cheaper and offer a higher EPA/DHA content, you may not be fully absorbing it because of a low bioavailability. This form of fish oil is not as stable as either triglyceride forms, which means it will spoil faster.

An interesting fact from the food industry: if EPA and DHA are added to foods such as baby formula or fortified foods, they will be in a triglyceride form due to the superior stability. Ethyl esters do not have the stability to be added to foods because they will oxidize quickly and add a rancid taste to the food. The tests done by the department of biotechnology at Tottori University in Japan showed that the ethyl ester form of DHA was less stable and produced more harmful oxidative by-products than the triglyceride DHA form [1].

Triglycerides Concentrate Form: This form of fish oil is converted from the ethyl ester form back into a triglyceride form after distillation and concentration. This is done by reacting the ethyl ester fish oil to separate the ethanol molecule and reattaching a glycerol backbone to the fatty acids. At the end, you get the best of both worlds — high bioavailability and levels of EPA and DHA. Don’t just trust us: in a recent study by the department of nutrition at the University of Copenhagen re-esterified triglycerides were superior to natural triglycerides by 124% in bioavailability [2].

How are Triglycerides absorbed compared to Ethyl Esters?

All dietary fats are broken down by digestive enzymes then absorbed in our small intestine. The main digestive enzymes that work to break down fats are bile salts and lipase. The bile salts separate the fat into tinier globs while the lipase breaks it down. In short, the fat is digested then absorbed into the intestinal wall and finally transported via chylomicrons to the blood.

This happens naturally with triglyceride based fish oil without a hiccup. The process of an ethyl ester is not exactly the same because of its form, the ethanol backbone. The lipase that normally breaks down fat takes 10-50 times longer to break down the ethanol based bond [3]. This may be higher in those with digestive issues or those who have a pathological condition that may impair digestion. This has been shown in individuals with cystic fibrosis where supplemental fish oil increased EPA/arachidonic acid ratio in plasma by 9.8 fold; much lower compared to the healthy individuals who increased their ratio by 23 fold [4].

The majority research in the clinical setting has been done with ethyl ester fish oil with funding from pharmaceutical companies due to their revenue stake in ethyl ester fish oil. Otherwise, the body of research shows triglycerides are superior to ethyl ester in terms of absorption and tissue integration.

A recent double-blind placebo controlled study with 72 subjects compared natural triglyceride, ethyl ester, and a triglyceride concentrate. The triglyceride concentrate was the best absorbed at 24% better than natural triglyceride, in contrast, the ester fish oil absorbed 27% less efficiently compared to the natural triglyceride [2]. The researchers speculated that was likely due to the lipase activity limiting the absorption of the ethyl ester fish oil. This study was only two weeks long; while it was able to measure the absorption of fish oil, it did not have a chance to take a good look at tissue integration.

A longer double-blind placebo study done for 6 months showed tissue integration measuring omega-3 index using a measure of DHA and EPA of the red blood cell. It was reported after 3 months omega-3 index was increased by 186% for the triglyceride group and 161% in the ethyl ester group. After 6 months, the ethyl ester group still could not catch up with 171% increase compared to the triglyceride group that had a measured increase of 197% [5].

Triglyceride concentrate based fish oils trump ethyl ester in omega-3 index even on a longer term scale, but it doesn’t just stop there. The study also showed that the triglyceride concentrate lowered blood triglyceride levels while the ethyl ester fish oil did not have an effect on this measure. High triglyceride levels contribute to the hardening of the arteries, which may increase risk of heart disease.

As you can see from the previous research, triglyceride based fish oils are a better choice for supplementation for absorption, tissue integration, and other possible biological benefits compared to ethyl ester fish oils.

How can I tell what form my fish oil is in?

Most fish oils are ethyl ester or re-esterified triglyceride based, though there are low cost fish oils that are natural triglyceride based due to the cheap raw ingredient sourcing used to produce it. The natural triglyceride fish oils are not distilled for impurities so we recommend staying away from those.

An easy way to find out which of the forms your fish oil was produced in is by reading the description on the bottle or on their respective website; usually fish oil products will list what form they are. If they don’t, there is a simple home test you can do:

  • Step 1: Take your fish oil that you want to test
  • Step 2: Get some styrofoam
  • Step 3: Coat the styrofoam with the fish oil in a glass cup and wait 5 minutes.

If the fish oil dissolves the styrofoam, it means it is an ethyl ester based fish oil. This happens due to the molecular form of the ethyl ester fish oil interacting with the styrofoam. This doesn’t necessarily mean it’ll do this to your stomach, but it is not very appealing.

Civic Nutrition fish oil pills come in re-esterified triglyceride form because it has the best bioavailability, concentration of EPA/DHA, shelf-life, while maintaining a low level of impurities.


  1. Yoshii H, Furuta T, Siga H, Moriyama S, Baba T, Maruyama K, Misawa Y, Hata N, Linko P. Autoxidation kinetic analysis of docosahexaenoic acid ethyl ester and docosahexaenoic triglyceride with oxygen sensor. Biosci Biotechnol Biochem. 2002 Apr;66(4):749-53.
  2. Dyerberg J, Madsen P, Møller JM, Aardestrup I, Schmidt EB. Bioavailability of marine n-3 fatty acid formulations. Prostaglandins Leukot Essent Fatty Acids. 2010 Sep;83(3):137-41.
  3. Yang LY, Kuksis A, Myher JJ. Lipolysis of menhaden oil triacylglycerols and the corresponding fatty acid alkyl esters by pancreatic lipase in vitro: a reexamination. J Lipid Res. 1990 Jan;31(1):137-47.
  4. Henderson, W.R., Jr., et al., Oral absorption of omega-3 fatty acids in patients with cystic fibrosis who have pancreatic insufficiency and in healthy control subjects. J Pediatr, 1994. 124(3): p. 400-8.
  5. Neubronner, J., et al., Enhanced increase of omega-3 index in response to long-term n-3 fatty acid supplementation from triacylglycerides versus ethyl esters. Eur J Clin Nutr, 2011. 65(2): p. 247-54.
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