What Should You Look for in Fish Oil? A Comprehensive Guide to Healthy Supplementation

October 23, 2025 •

4 min read

Over 90% of Americans may not consume enough omega-3 fatty acids from diet alone, making supplementation a popular option. Navigating the market can be challenging, so it's crucial to understand what should you look for in fish oil to ensure you are investing in a product that is both effective and safe.

Quick Summary

This guide details the essential criteria for selecting a high-quality fish oil supplement, focusing on label transparency, potent EPA and DHA levels, third-party purity testing, and the importance of freshness and sustainable sourcing.

Key Points

Check EPA and DHA Potency: Focus on the specific amounts of EPA and DHA per serving, not just the total fish oil amount.
Insist on Third-Party Testing: Look for certifications like IFOS, NSF, or USP to ensure the product is free of heavy metals and other contaminants.
Prioritize Freshness: Avoid rancid oil by checking the expiration date and for a non-fishy smell; look for a low TOTOX score on IFOS reports.
Choose the Right Form: The triglyceride form is generally considered more bioavailable and stable than the ethyl ester form.
Select Sustainable Sourcing: Opt for fish oil derived from small, wild-caught fish like anchovies and sardines, often indicated by MSC or Friend of the Sea certifications.
Ensure Transparency: High-quality brands will be transparent about their sourcing, testing, and production methods.

Why Quality Matters in Fish Oil

Fish oil supplements are a rich source of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), two omega-3 fatty acids that play vital roles in supporting cardiovascular health, brain function, and reducing inflammation. However, not all fish oil is created equal. Poor-quality or rancid oil can be less effective and may even be harmful. Knowing how to evaluate a supplement based on potency, purity, freshness, and form is essential for reaping the full benefits of this nutrient.

Potency: Focusing on EPA and DHA Levels

When evaluating a fish oil supplement, the total amount of fish oil listed on the bottle is less important than the specific quantity of EPA and DHA. A product may contain a certain amount of fish oil, but a much lower concentration of the active omega-3s. The benefits are primarily linked to the EPA and DHA content. Health experts often highlight the importance of adequate daily intake of EPA and DHA for most healthy adults, with varying amounts sometimes recommended for specific health conditions, under medical supervision.

Read the Supplement Facts Panel: Always turn the bottle over and check the detailed breakdown on the back panel. Look for the milligrams (mg) of EPA and DHA per serving.
Consider Concentration: A higher concentration can mean you get more active omega-3s in fewer capsules, which can be more convenient.

Purity: Ensuring Freedom from Contaminants

Fish can accumulate environmental toxins such as mercury, lead, PCBs, and dioxins. High-quality fish oil undergoes a purification process, such as molecular distillation, to remove these harmful contaminants. To confirm a product's purity, look for proof of third-party testing.

Look for Third-Party Certifications: Independent organizations test and certify fish oil products to ensure they meet stringent standards for purity and potency. Look for seals from reputable organizations, such as:
- IFOS (International Fish Oil Standards): The IFOS 5-star rating indicates that a product has met high standards for potency, purity, stability, and safety.
- NSF International: Certifies that supplements are tested for harmful levels of contaminants.
- USP (U.S. Pharmacopeia): Ensures that the product contains the ingredients listed on the label and is free of contaminants.

Freshness: Avoiding Oxidation and Rancidity

Omega-3 fatty acids are susceptible to oxidation, which causes the oil to go rancid. Oxidized fish oil can be less effective and may cause unpleasant fishy burps or have a negative health impact. Quality brands take steps to protect their products from spoilage.

Check the Smell and Taste: A fresh, high-quality fish oil should not have an overpowering or foul fishy odor. Strong fishy burps can indicate the oil may be rancid. Some products add antioxidants like vitamin E or rosemary extract to preserve freshness.
Look for Freshness Markers: The IFOS certification includes tests for oxidation, providing a total oxidation value (TOTOX) that indicates freshness.
Proper Storage: Always store fish oil in a cool, dark place, and ideally in the refrigerator after opening, to slow down oxidation.

Form: Triglycerides vs. Ethyl Esters

Fish oil supplements are available in several forms, most commonly natural triglycerides (TG) and ethyl esters (EE).

Triglyceride Form (TG/rTG): This is the natural form of fat found in fish and is generally considered more bioavailable and easier for the body to absorb.
Ethyl Ester Form (EE): Created during the concentration and purification process, the EE form is a synthetic intermediate. It is often less expensive but may not be absorbed as efficiently as the TG form. Some manufacturers re-esterify the oil back into a triglyceride form (rTG) to improve bioavailability.

Comparison of Fish Oil Forms


Feature	Triglyceride (TG/rTG)	Ethyl Ester (EE)
Absorption	Generally superior and more efficient.	Less readily absorbed; requires extra digestion steps.
Stability	More stable and resistant to oxidation.	Less stable, making it more prone to rancidity.
Cost	Typically more expensive due to additional processing steps.	Generally more affordable to produce.
Naturalness	Closest to the natural form of omega-3s found in fish.	Chemically modified, synthetic form.

Sustainability and Sourcing

Ethical and environmental considerations are important when choosing a fish oil supplement. Overfishing and sourcing practices can have a significant impact on marine ecosystems.

Source from Small Fish: Choosing oil derived from smaller fish, such as anchovies and sardines, is often considered more sustainable. These fish reproduce faster and are lower on the food chain, meaning they may accumulate fewer toxins.
Look for Certifications: Certifications like the Marine Stewardship Council (MSC) or Friend of the Sea indicate that the fish were sourced responsibly from sustainable fisheries.

Conclusion: Making an Informed Choice

Choosing a high-quality fish oil supplement involves considering several factors beyond the total milligrams. By prioritizing potency (high EPA and DHA content per serving), verifying purity through third-party certifications, ensuring freshness, and opting for forms like the triglyceride that may offer better bioavailability, you can make a more informed choice about your supplementation. Paying attention to sustainable sourcing from smaller fish also supports environmental responsibility. Always read the label carefully and consider your individual needs and budget before making a purchase. If in doubt, consulting a healthcare professional is a wise step.

For further information on certification standards, visit the IFOS website.

Frequently Asked Questions

While both contain omega-3 fatty acids EPA and DHA, cod liver oil also contains significant amounts of vitamins A and D. This can be a concern for pregnant women due to the risk of vitamin A toxicity, so general fish oil may be a safer choice.

Rancid or oxidized fish oil often has a strong, foul, fishy smell or taste. Fresh, high-quality fish oil should have a neutral or mildly pleasant smell, often masked with a citrus or other natural flavor.

The triglyceride form is more bioavailable, meaning it is more efficiently absorbed and utilized by the body. It is also the natural form found in fish, making it more stable and less prone to oxidation.

Third-party testing involves sending a supplement to an independent laboratory for verification of its contents, purity, and potency. It is important because it provides an unbiased assessment, ensuring the product is safe and contains what the label claims.

Yes, sourcing fish oil from smaller fish like anchovies and sardines is often preferred. These fish have shorter lifespans and are lower on the food chain, which means they tend to accumulate fewer heavy metals and toxins.

For most people, regular supplementation can be beneficial, especially if dietary intake of fatty fish is low. It is always advisable to follow product instructions or consult with a healthcare professional for personalized guidance.

Yes, plant-based sources like algal oil provide EPA and DHA directly, similar to fish oil. Other plant sources like flaxseed contain ALA, which the body must convert to EPA and DHA, a conversion process that is often inefficient.