Understanding Fish Oil Forms: What's the best form of fish oil to take?

October 6, 2025 •

4 min read

Over one billion dollars is spent annually on fish oil supplements in the United States, yet many consumers are unaware that not all forms are created equal. Deciding on what's the best form of fish oil to take depends heavily on understanding the different molecular structures and their impact on absorption and efficacy. This guide breaks down the science to help you make an informed choice.

Quick Summary

Different molecular structures like natural triglycerides, ethyl esters, and re-esterified triglycerides affect how the body absorbs omega-3s. The ideal choice depends on absorption efficiency, stability, concentration, and personal dietary needs. Key factors include bioavailability, freshness, and third-party testing for purity.

Key Points

Triglyceride Forms are Superior for Absorption: Natural (TG) and re-esterified (rTG) triglycerides are the most bioavailable forms, meaning your body absorbs and uses them more efficiently than ethyl esters.
Ethyl Esters are Less Bioavailable and Stable: While often cheaper and highly concentrated, ethyl esters (EE) are less stable and less effectively absorbed, potentially causing fishy burps.
Prioritize Third-Party Purity Testing: Look for supplements certified by organizations like IFOS or NSF to ensure they are free from heavy metals, PCBs, and other contaminants.
Check for Freshness and Prevent Rancidity: High-quality fish oil should have no strong fishy smell. Choose products in light-blocking containers that contain antioxidants like vitamin E.
Consider Alternatives like Krill or Algae Oil: Krill oil offers omega-3s in a highly-absorbable phospholipid form, while algal oil is a potent, sustainable, and vegan source of DHA and EPA.
Focus on EPA and DHA Levels, Not Just Total Fish Oil: The label should clearly state the amount of active EPA and DHA per serving. A higher concentration in a smaller dose is often a sign of a better product.

Understanding the Different Forms of Fish Oil

Fish oil provides essential omega-3 fatty acids, primarily eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which support brain, heart, and joint health. However, the supplement market offers several forms, each with distinct characteristics regarding absorption and stability. The two most common forms are triglycerides and ethyl esters, but reformed triglycerides and other sources like krill and algae also exist.

Natural and Reformed Triglycerides (TG and rTG)

Triglycerides (TG) are the natural form of fat found in fish and how fats are typically stored in the human body. This molecular structure is highly recognizable and efficiently processed by the body, leading to superior absorption.

Natural Triglyceride (TG): This is the oil extracted directly from fish tissue. While highly bioavailable, it is less concentrated, meaning you might need to take more capsules to reach your desired dosage of EPA and DHA.
Re-esterified Triglyceride (rTG): This form starts as a concentrated ethyl ester but is processed a second time to convert it back into a triglyceride structure. This provides the high concentration of EE with the superior bioavailability and stability of natural TG, making it a premium and effective option, albeit more expensive.

Ethyl Esters (EE)

To produce more concentrated omega-3 supplements, manufacturers convert the natural triglyceride oil into an ethyl ester form through a chemical process. This is a cost-effective way to increase the levels of EPA and DHA per capsule.

Lower Bioavailability: Studies show that ethyl esters are absorbed less efficiently than triglyceride forms, sometimes by a significant margin. The body must first process the EE form back into a TG structure before it can be effectively absorbed.
Reduced Stability: EE forms are more prone to oxidation and can go rancid faster than their triglyceride counterparts. This is often the cause of unpleasant fishy burps experienced by some users.

Alternative Omega-3 Sources

Krill Oil: Extracted from small shrimp-like marine animals, krill oil contains omega-3s in a phospholipid form. This structure is easily absorbed and is naturally resistant to oxidation due to the antioxidant astaxanthin.
Algal Oil: A vegetarian and vegan-friendly option, algal oil is derived from marine algae, the original source of omega-3s in the marine food chain. It is a high-quality, pure source of EPA and DHA that is highly bioavailable and environmentally sustainable.

How to Choose the Right Supplement

When deciding on the best form of fish oil to take, several factors beyond molecular structure are crucial for ensuring quality and effectiveness.

Third-Party Testing and Purity

Reputable fish oil supplements should undergo third-party testing by organizations like the International Fish Oil Standards (IFOS) or NSF International. These tests verify the product’s purity, potency, and freshness, ensuring it is free from contaminants like mercury, PCBs, and dioxins.

Freshness

Omega-3 fatty acids are delicate and can easily oxidize. A fresh, high-quality supplement should not have a strong, fishy odor or taste. Many companies add antioxidants like vitamin E to their products to prevent rancidity. Always check the expiration date and consider liquid forms stored in the refrigerator.

Concentration (EPA and DHA Content)

Don't just look at the total fish oil amount on the label; focus on the specific levels of EPA and DHA per serving. A high-quality supplement will provide a potent, concentrated dose in a smaller serving.

Sustainability

To support responsible sourcing, look for certifications from organizations like the Marine Stewardship Council (MSC) or Friend of the Sea. Choosing oil from smaller, cold-water fish like anchovies and sardines is also a more sustainable option.

Form Comparison: Triglyceride vs. Ethyl Ester


Feature	Triglyceride (TG)	Ethyl Ester (EE)
Bioavailability	Highest absorption rate; natural form.	Lower absorption rate; requires extra processing in the body.
Stability	More stable and less prone to oxidation.	Less stable and more susceptible to rancidity.
Cost	Generally more expensive due to complex processing.	Less expensive to produce, often more affordable.
Concentration	Natural TG has lower concentration; rTG is highly concentrated.	Can achieve high concentrations of EPA and DHA.
Digestive Tolerance	Easier on the digestive system; fewer fishy burps.	Higher risk of fishy burps and digestive discomfort.

Conclusion

For most people, the natural triglyceride (TG) or re-esterified triglyceride (rTG) form offers the best combination of high bioavailability and stability, making them the most effective choice for supplementing omega-3s. While ethyl ester (EE) versions are cheaper and concentrated, their lower absorption rate and instability can make them a less optimal choice. Vegan or vegetarian individuals should opt for high-quality algal oil to get their DHA and EPA directly. Regardless of the form, it is crucial to select a supplement that is third-party tested for purity and freshness to ensure you are getting a safe and effective product.

This content is for informational purposes only and does not constitute medical advice. Consult a healthcare professional before starting any new supplement.

Frequently Asked Questions

The primary difference is the molecular structure, which impacts absorption. Triglyceride is the natural, highly-absorbable form, while ethyl ester is a processed, semi-synthetic form that the body absorbs less efficiently.

Check the label for 'natural triglyceride,' 're-esterified triglyceride,' 'rTG,' or 'TG.' Some products may not explicitly state the form, but a higher price point often indicates a triglyceride base.

Fishy burps are a common sign of oxidized or rancid oil, which is more likely to occur with the less stable ethyl ester form. Choosing a fresher, triglyceride-based supplement can help minimize this issue.

Yes, algal oil is an excellent alternative, especially for vegetarians and vegans. Since fish get their omega-3s from algae, this oil provides a direct, pure, and sustainable source of DHA and EPA.

Not necessarily. Higher concentrations can be beneficial, but potency is measured by the actual EPA and DHA content. Always check the label for these specific amounts, and consult a healthcare professional for the right dosage.

Third-party certifications from organizations like IFOS or NSF verify that the supplement's contents match its label and that it has been tested for purity, potency, and contaminants like mercury and PCBs.

While both contain omega-3s, cod liver oil also contains significant levels of vitamins A and D. It is generally recommended to take one or the other to avoid excessive intake of these fat-soluble vitamins, which can be harmful in high doses.