What's the difference between fish oil and omega three? Understanding Sources and Nutrients

October 24, 2025 •

3 min read

According to the National Institutes of Health, omega-3 fatty acids are essential nutrients that the body cannot produce on its own. This makes it crucial to understand what's the difference between fish oil and omega three, as one is a source and the other is the nutrient itself, a detail often misunderstood by consumers.

Quick Summary

Fish oil is a dietary supplement derived from fish tissue that contains omega-3s, which are essential fatty acids. Omega-3s are the beneficial nutrients, found in both marine and plant sources, with the most active forms being EPA and DHA.

Key Points

Fish oil is a source, while omega-3 is the nutrient: Fish oil contains omega-3 fatty acids, but the term 'omega-3' refers to the group of essential fatty acids themselves.
Omega-3s come in three main forms: These are ALA (from plants), EPA, and DHA (from marine sources). EPA and DHA are the most bioactive forms for humans.
ALA conversion is inefficient: The body converts plant-based ALA to the more beneficial EPA and DHA, but the process is very limited, making marine sources more effective for boosting active omega-3 levels.
Not all supplements are equal: The quality and concentration of EPA and DHA vary widely among supplements; look for third-party testing and specific dosages.
Fish oil isn't the only marine source: Krill oil and algal oil are also rich in EPA and DHA, with algal oil being a viable vegan alternative.
Whole food intake is ideal: Eating fatty fish like salmon provides not just omega-3s but other beneficial nutrients, often offering better overall health outcomes than supplements alone.

Demystifying Omega-3 Fatty Acids

Omega-3 fatty acids are a group of essential polyunsaturated fats vital for various bodily functions, including inflammation control, brain health, and cell structure. Since the body cannot produce them, they must be consumed through diet or supplementation.

There are three primary omega-3 fatty acids:

Alpha-linolenic acid (ALA): Primarily from plant sources like flaxseeds, walnuts, and chia seeds. The body can convert ALA to EPA and DHA, but inefficiently.
Eicosapentaenoic acid (EPA): Found mainly in fatty fish; supports heart health and has anti-inflammatory effects.
Docosahexaenoic acid (DHA): Also found in fatty fish; crucial for brain and eye development and function.

Due to the poor conversion of ALA, consuming EPA and DHA directly from marine sources is often recommended.

What Exactly is Fish Oil?

Fish oil is fat extracted from the tissues of oily fish such as salmon and mackerel. It is a concentrated source of the omega-3s EPA and DHA. Fish oil supplements provide these specific omega-3s, sometimes with other fats and fat-soluble vitamins.

The concentration of EPA and DHA varies between products. High-quality fish oils are purified to remove contaminants like mercury.

The Core Distinction: Source vs. Nutrient

The key difference is that omega-3 is the nutrient—the fatty acid—while fish oil is one source of that nutrient. Think of it like an orange containing vitamin C; omega-3s are found in fish oil, but also in other sources like algae and plants. This distinction is important for understanding product labels.

Exploring Different Omega-3 Sources

Besides fish oil, other sources provide omega-3s:

Krill Oil: From small crustaceans, it contains EPA and DHA, often in phospholipid form which may enhance absorption. It also contains astaxanthin.
Algal Oil: A vegan source of pre-formed EPA and DHA derived from algae, the original producers of these marine omega-3s. It has a lower risk of contaminants.
Plant-Based Sources: Flaxseeds and walnuts provide ALA, which the body converts to EPA and DHA inefficiently.

Health Benefits and Supplement Quality

Omega-3s from various sources support heart and brain health and reduce inflammation. Supplement quality is crucial for effectiveness.

How to Choose a Quality Omega-3 Supplement

Check the Concentration: Ensure the label lists sufficient amounts of EPA and DHA.
Look for Third-Party Certifications: Certifications like IFOS or NSF verify purity and potency.
Ensure Freshness: Avoid products with a strong fishy smell. Antioxidants like Vitamin E help prevent rancidity.
Consider Bioavailability: Some formulations like re-esterified triglycerides (rTG) may offer better absorption.

Comparison: Fish Oil vs. Omega-3 Sources


Feature	Fish Oil	Omega-3s	Algal Oil	Krill Oil
Classification	A source of nutrients	The nutrient (fatty acid)	A source of nutrients	A source of nutrients
Key Components	EPA, DHA, other fats	EPA, DHA, ALA	Primarily EPA, DHA	EPA, DHA, Astaxanthin
Sources	Oily fish (e.g., salmon, mackerel)	Fish, algae, plants	Algae	Antarctic krill
Absorption Form	Mostly natural triglycerides or ethyl esters	Varies by source	Mostly triglycerides	Phospholipids
Contaminants	Risk of mercury/PCBs (removed in purified oil)	Varies by source	Minimal risk	Minimal risk
Best For	Those seeking a direct source of EPA and DHA	General term for the fatty acid class	Vegans/vegetarians or those concerned with contaminants	Individuals seeking highly bioavailable EPA and DHA with added antioxidants

Conclusion

Fish oil contains omega-3s, but omega-3s are not solely found in fish oil. Omega-3 is the nutrient, and fish oil is a source. Understanding this helps in making informed dietary choices. Fish oil supplements are beneficial for those who don't eat fatty fish regularly. Vegan options like algal oil provide EPA and DHA. Choosing a high-quality, third-party-tested product is essential. A balanced diet with whole foods and, if needed, a quality supplement is key for adequate omega-3 intake.

For additional nutritional details on omega-3 fatty acids, refer to resources like the National Institutes of Health (NIH) Office of Dietary Supplements.

Disclaimer: Consult a healthcare professional before starting any new supplement regimen, especially if you are pregnant, breastfeeding, or have pre-existing health conditions.

Frequently Asked Questions

No, they are not the same. Fish oil is a supplement source that contains omega-3 fatty acids, which are the active nutrients. It’s like the difference between a milk carton and the milk inside.

The three main types are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA).

Fish oil is rich in EPA and DHA, the two types of omega-3 fatty acids that are most beneficial for heart and brain health. It typically does not contain ALA.

For most people, getting omega-3s from whole foods like fatty fish is recommended, as it provides a broader range of nutrients. However, supplements are a useful alternative for those who don't eat fish regularly.

Both contain EPA and DHA. However, the omega-3s in krill oil are primarily in phospholipid form, which may be more bioavailable, and krill oil also contains the antioxidant astaxanthin.

Yes. Vegans can get ALA from plant sources like flaxseeds and walnuts. To get the more active EPA and DHA, they can use supplements derived from algae (algal oil).

Look for products that specify high levels of EPA and DHA, have third-party certifications (like IFOS), list the concentration clearly, and are stored to prevent rancidity.