Fish Oils
Unless specified (Cod Liver, Salmon etc.), most fish oils come from anchovies. These are caught off the coast of Peru (and similar locations) and then shipped to their destination (often China) for processing into the oil and softgels. Depending on catches, the oil may be a mixture with other oily fish such as mackerel.
Oil is rendered from the fish by heating. Fish oil naturally contains around 20–30% Omega-3s (as EPA and DHA), which is why most standard anchovy oils are sold as 18/12 (18% EPA, 12% DHA).
Forms: EE, nTG and rTG
Most fish oil and Omega-3 softgels come in either EE (ethyl ester) or TG (triglyceride) form. The TG form can be sub-divided into nTG and rTG.
- nTG (natural triglyceride) – the oil as it comes from the fish. This is what we have, and what most people have.
- EE (ethyl ester) – the oil has been processed further, with chemicals, to purify and concentrate it. This is why EE forms have higher EPA/DHA amounts.
- rTG (re-esterified triglyceride) – the oil has been processed into EE, concentrated, and then converted back into a TG form. This makes it more "natural" in structure while keeping the higher concentration.
Therefore, EE and rTG are not technically natural. Scientific studies have shown very similar benefits from EE and TG forms, so one is not necessarily better than the other.
Why natural oils stop at around 30%
In a natural triglyceride, each molecule carries three fatty acids, and EPA and DHA are attached alongside saturated and monounsaturated fats on the same molecule. Because the Omega-3s are chemically bound to the fats you would want to remove, they cannot simply be filtered out. A natural, unconcentrated fish oil therefore stays at roughly 30% EPA + DHA.
Higher concentrations
High-strength oils such as 50/25 (around 75% EPA + DHA) cannot be made without further processing. They are normally made by converting the oil to ethyl esters, concentrating it by molecular distillation and/or urea complexation (which can reach 60–90% Omega-3), and, for TG products, re-esterifying back onto glycerol. In practice, a high-concentration TG oil is almost always rTG.
Some routes give a modest increase while keeping the oil as a triglyceride:
| Method / source | Typical EPA + DHA | Notes |
|---|---|---|
| Standard anchovy oil (nTG) | approx. 30% | Usually sold as 18/12 |
| Species selection (e.g. tuna oil) | approx. 30% | Naturally DHA-rich, roughly 5–7% EPA / 22–27% DHA |
| Winterisation | up to approx. 35% | Oil is chilled so the more saturated triglycerides crystallise and are filtered off |
| Enzymatic (lipase) or supercritical CO₂ fractionation | approx. 40–50% | Still processing; leaves mono- and diglycerides |
| EE / rTG concentrates | 60–90% | Fully processed; not natural |
| Algal oil (not fish) | approx. 40–55% DHA | Natural TG from algae; vegan alternative |
Checking a supplier's "natural TG" claim
If a supplier offers a high-concentration oil described as natural TG, ask for:
- Triglyceride content (%) on the CoA – rTG is often only about 60–90% TG, with the remainder as di- and monoglycerides. True nTG is close to 100%.
- Positional analysis (¹³C NMR) – in natural fish oil, DHA sits mainly in the middle (sn-2) position of the molecule; in rTG it is spread randomly.
- The process flowchart – any ethanolysis, ethyl ester or re-esterification step means it is not natural TG.
- The units – make sure "50/25" means percentages, and not mg per capsule or per multi-capsule serving.
References
- Bioavailability of TG vs EE forms (thorough article): https://wileysfinest.com/what-does-science-say-bioavailability-of-triglyceride-vs-ethyl-ester-forms-of-fish-oil/