Fish oil and omega-3 are not the same thing. Fish oil is a supplement that contains omega-3 fatty acids, but omega-3s are a broader category of nutrients found in many sources beyond fish. Think of it this way: fish oil is the delivery vehicle, and omega-3s are the active ingredients inside it.
What’s Actually Inside a Fish Oil Capsule
A standard 1,000 mg fish oil capsule contains only about 300 mg of actual omega-3 fatty acids, specifically 180 mg of EPA and 120 mg of DHA. The remaining 700 mg is other fats. This is why the number on the front of a supplement bottle can be misleading. The front label shows the total fish oil per capsule, but only a fraction of that, sometimes as little as 25%, is the EPA and DHA your body actually uses.
To find the real omega-3 content, flip the bottle over and check the nutrition facts panel on the back. Look for the individual EPA and DHA amounts listed per serving. If a healthcare provider recommends 1,000 mg of omega-3s, they typically mean 1,000 mg of combined EPA and DHA, which could require two or three standard capsules depending on the brand.
Three Types of Omega-3s
There are three main omega-3 fatty acids, and they come from very different sources. EPA and DHA are the two found in fish oil, and they’re the forms your body can use directly. They play roles in heart health, brain function, and managing inflammation. The third type, ALA, comes from plant foods like flaxseed, chia seeds, and walnuts.
ALA is technically an omega-3, but your body has to convert it into EPA and DHA before it can do much with it. That conversion is remarkably inefficient. Healthy adults convert roughly 5 to 10% of ALA into EPA, and the conversion to DHA is even worse, likely under 5% and possibly closer to 1%. So while a tablespoon of flaxseed oil is rich in omega-3s on paper, it delivers far less usable EPA and DHA than a serving of fish oil or fatty fish.
Fish Oil Isn’t the Only Source of EPA and DHA
If you don’t eat fish or prefer a plant-based option, algal oil (made from microalgae) provides both EPA and DHA without the fish. This makes sense biologically: fish accumulate their omega-3s by eating algae in the first place, so algal oil cuts out the middleman. A study published in the International Journal of Molecular Sciences found that after 14 weeks of supplementation, the bioavailability of DHA and EPA from microalgal oil was comparable to fish oil when adjusted for dose. Your body absorbs the omega-3s equally well from either source.
The ratio of EPA to DHA differs, though. Fish oil tends to be higher in EPA relative to DHA (roughly a 3:2 ratio), while algal oil from common species like Schizochytrium is heavier on DHA (roughly a 3:1 DHA-to-EPA ratio). For most people this distinction doesn’t matter much, but it’s worth knowing if you’re trying to hit a specific target for one or the other.
Not All Fish Oil Supplements Absorb the Same Way
The form of omega-3 inside a supplement affects how well your body absorbs it. Natural fish oil stores its omega-3s as triglycerides, which is the same form found in whole fish. Many cheaper supplements use a processed form called ethyl esters, which your body absorbs about 27% less efficiently than natural triglycerides. On the other end, re-esterified triglycerides (a refined version that concentrates the omega-3 content) absorb about 24% better than natural fish oil.
You can usually find the form listed on the supplement label or the manufacturer’s website. If it says “triglyceride form” or “rTG,” you’re getting the better-absorbed version. If it just says “fish oil concentrate” with no specifics, it’s likely ethyl ester. This matters practically because a supplement with lower bioavailability means you need to take more capsules to get the same benefit.
How Much EPA and DHA You Actually Need
A standard fish oil capsule with 300 mg of combined EPA and DHA falls short of what most health organizations suggest for general wellness. Two servings of fatty fish per week, roughly equivalent to 250 to 500 mg of EPA and DHA per day, is a common baseline recommendation. People supplementing for specific health goals often take higher amounts under medical guidance.
The key takeaway for label reading: always base your dosing on the EPA and DHA numbers, not the total fish oil. A capsule advertising 1,200 mg of fish oil might contain less omega-3 than a capsule advertising 600 mg of concentrated omega-3s. The total fish oil number tells you the size of the capsule. The EPA and DHA numbers tell you what’s actually in it that matters.