How to Tell if a Fish Oil Supplement Is Good

November 26, 2025 •

4 min read

According to the Global Organization for EPA and DHA Omega-3s (GOED), 90% of the global population is deficient in omega-3s, but not all fish oil supplements are created equal. The key to reaping the cardiovascular, brain, and anti-inflammatory benefits lies in knowing how to tell if a fish oil supplement is good.

Quick Summary

Guide to identifying high-quality fish oil supplements. Focus on verifying potency by checking EPA and DHA levels, assessing freshness by avoiding rancid oil, and confirming purity with third-party testing. Look for specific certifications and the proper molecular form to ensure effectiveness.

Key Points

Check EPA and DHA Levels: Focus on the specific amounts of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) per serving, not just the total fish oil quantity.
Look for Third-Party Certification: Seek out certifications from organizations like IFOS, GOED, or NSF to ensure product purity, potency, and safety.
Assess Freshness: A fresh, high-quality fish oil should not smell or taste strongly fishy. Look for added antioxidants like Vitamin E.
Choose the Right Molecular Form: Prioritize supplements in the natural triglyceride (TG) or re-esterified triglyceride (rTG) form for better absorption.
Verify Sustainability: Check for seals from organizations like the Marine Stewardship Council (MSC) to ensure the fish were sourced ethically and responsibly.
Inspect the Packaging: Quality fish oil is often sold in dark, opaque bottles to protect the oil from light-induced oxidation.

Decoding the Label: Potency and Bioavailability

Not all fish oil supplements contain the same amount of beneficial omega-3 fatty acids, namely eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). A product claiming 1,000 mg of “fish oil” per capsule might only contain 300 mg of the crucial EPA and DHA. A high-quality supplement will prominently list the specific amounts of EPA and DHA per serving on the 'Supplement Facts' panel, with a recommended combined intake often ranging from 500mg to over 1,000mg per day, depending on individual health goals.

Molecular Form: Triglyceride vs. Ethyl Ester

Another critical factor is the oil's molecular structure, which affects how well your body absorbs it. Fish oil comes primarily in two forms: natural triglyceride (TG) and ethyl ester (EE). The natural triglyceride form is how omega-3s are found in fish and is generally considered more bioavailable and easier for the body to absorb. Some manufacturers, to increase concentration, convert the oil into the ethyl ester form during processing, which is less efficiently absorbed. Re-esterified triglycerides (rTG) convert the ethyl ester form back into a more absorbable state but are more expensive to produce. Checking the fine print on the supplement label can reveal which form the product contains.

Checking for Freshness: The Smell Test and Additives

Fish oil is highly prone to oxidation, a process that can cause it to become rancid. Rancid fish oil not only has an unpleasant, fishy taste and smell but may also be less effective or even harmful, potentially contributing to inflammation.

Signs of a Fresh Supplement

Mild Smell: A high-quality, fresh fish oil should not smell strongly or unpleasantly fishy. While some products have added flavors to mask taste, a strongly fishy odor can indicate spoilage.
Added Antioxidants: Reputable brands often add natural antioxidants like Vitamin E or rosemary extract to their formulas to protect the oil from oxidation and extend its shelf life.
Opaque Packaging: Light exposure accelerates oxidation, so quality fish oil is often sold in dark, opaque bottles to protect it.

The Role of Third-Party Testing and Certification

Because supplement regulations can be inconsistent, third-party testing is a crucial indicator of a product’s quality, purity, and potency. Independent labs rigorously test for contaminants and verify label claims.

Key Certifications to Look For

IFOS (International Fish Oil Standards): A highly respected third-party program that assigns a star rating based on testing for potency, purity, stability, and heavy metals. Consumers can check batch-specific reports on the IFOS website.
GOED (Global Organization for EPA and DHA Omega-3s): Ensures products meet high quality and safety standards.
NSF International / USP Certification: Verifies that a supplement contains the ingredients and amounts listed on the label and is free of harmful contaminants.
Marine Stewardship Council (MSC) / Friend of the Sea: These certifications verify that the fish were sourced sustainably and responsibly.

Comparison of High-Quality vs. Low-Quality Fish Oil


Feature	High-Quality Fish Oil	Low-Quality Fish Oil
Potency (EPA/DHA)	Clearly lists high, concentrated levels of EPA and DHA per serving.	Lists a high total fish oil amount, but low concentrations of actual EPA/DHA.
Purity	Rigorously tested for heavy metals (mercury), PCBs, and dioxins. Certification available.	Minimal to no third-party testing; higher risk of contaminants.
Freshness	Protected from oxidation with antioxidants and opaque bottles. Not rancid.	Prone to oxidation; may have a fishy smell or cause "fishy burps".
Form	Often sold in natural triglyceride (TG) or re-esterified triglyceride (rTG) form for better absorption.	Commonly sold in less absorbable ethyl ester (EE) form.
Sustainability	Sourced from smaller, wild-caught fish from clean, regulated waters. Certified by organizations like MSC.	Sourced from unverified or potentially unsustainable fisheries.

Conclusion: Making an Informed Choice

To find a truly effective fish oil supplement, a savvy consumer must look beyond just the price tag and total fish oil content. Prioritize products with high, specified levels of EPA and DHA in a natural or re-esterified triglyceride form. Always verify the supplement's purity and freshness by checking for third-party certifications from reputable organizations like IFOS, GOED, or NSF. Considering the source of the fish and ensuring sustainable practices with seals like MSC or Friend of the Sea is an added layer of quality assurance. By following these steps, you can confidently select a product that delivers the promised health benefits of omega-3 fatty acids. For additional verification, consumers can research specific brands and their certifications online before making a purchase.

Citations

Bare Biology. (2017, October 10). 6 Tips for Choosing the Best Fish Oil. Retrieved from https://www.barebiology.com/blogs/news/six-factors-to-consider-when-buying-an-omega-3-supplement
Hindustan Times. (2025, July 12). Nutritionist shares tips to choose the best fish oil supplement for health benefits. Retrieved from https://www.hindustantimes.com/lifestyle/health/nutritionist-shares-tips-to-choose-the-best-fish-oil-supplement-for-health-benefits-101751536265093.html
Wellbeing Nutrition. (2025, September 16). Fish Oil Capsules: What to Look for and How to Pick the Best. Retrieved from https://wellbeingnutrition.com/blogs/weight-metabolism/how-to-choose-the-best-fish-oil-capsules-for-your-needs
Icelandirect. (2025, May 14). How to Verify High Quality Fish Oil Supplements. Retrieved from https://icelandirect.com/verify-high-quality-fish-oil-supplements/
NATURELO Premium Supplements. (2020, August 03). The Secret of How to Choose the Best Fish Oil Supplement. Retrieved from https://naturelo.com/blogs/articles/how-to-choose-a-quality-fish-oil-supplement
WHC. (2025, May 12). Fish Oil Selection Guide: What is IFOS Certification?. Retrieved from https://whc.com.hk/en/blogs/whc/%E9%AD%9A%E6%B2%B9%E6%8C%91%E9%81%B8%E6%8C%87%E5%8D%97-%E4%BB%80%E9%BA%BC%E6%98%AFifos%E8%AA%8D%E8%AD%89-%E6%B7%B1%E5%85%A5%E8%A7%A3%E6%9E%90%E9%AD%9A%E6%B2%B9%E7%9A%84%E5%9C%8B%E9%9A%9B%E6%AC%8A%E5%A8%81-%E8%BA%AB%E4%BB%BD%E8%AD%89
Everyday Health. (2025, July 31). Is It Okay to Take Expired Fish Oil?. Retrieved from https://www.everydayhealth.com/food-ingredients/side-effects-of-fish-oil-pills-with-an-expired-date/
Essential Health SF. (2025, May 20). Fake Fish Oil? 5 Ways to Know If Your Supplement Is Actually Hurting You. Retrieved from https://www.essentialhealthsf.com/blog/pureorrancidfishoils

Frequently Asked Questions

The most important thing to look for is the specific amount of EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) listed per serving, not the overall milligrams of fish oil.

A rancid fish oil supplement will have a strong, unpleasant, or overly fishy smell and taste. Fresh fish oil should have a mild, clean scent or no fishy smell at all.

Third-party testing by independent organizations verifies that the product contains the stated amount of omega-3s and is free from harmful contaminants like mercury, PCBs, and dioxins.

Natural triglyceride (TG) form is generally considered more bioavailable and is better absorbed by the body than the ethyl ester (EE) form. Look for labels that specify 'triglyceride form'.

It is generally recommended to store fish oil in a cool, dark place. Liquid fish oil should be refrigerated after opening to maintain freshness. For capsules, follow the storage instructions on the bottle, but avoiding excessive heat and light is key.

An IFOS (International Fish Oil Standards) certification signifies that an independent third-party has tested the product and verified its purity, potency, freshness, and safety.

Not always. While enteric coatings or flavorings can reduce fishy burps, they can also mask the taste of a rancid or low-quality product. Checking for freshness with the 'smell test' is more reliable.

The source of the fish matters because smaller, wild-caught fish from cleaner, regulated waters (like sardines and anchovies) typically contain lower levels of mercury and other pollutants compared to larger, predatory fish.