Omega-3: The Complete Guide

Omega-3 is one of the most well-researched nutrients in existence. The evidence for it spans cardiovascular health, brain function, mood, inflammation, joints, and eye health. It’s also one of the most popular supplements in the world, with billions of dollars of fish oil sold every year.

And yet, when tested, the majority of people have omega-3 levels that are significantly lower than they should be. Some aren’t supplementing at all. But many of them are, and they’ve been taking fish oil for years. So what’s going wrong?

There are two problems. The first is that most people don’t get enough omega-3 from their diet to begin with, and the reasons for that go deeper than simply not eating enough fish. The second is that a large portion of the fish oil supplements on the market are either so low in dose that they make almost no difference, or they’re in a form the body struggles to absorb properly.

This article covers both of those problems in full: what omega-3 actually does and why it matters, how to test whether you’re getting enough, how to choose a supplement that works, and specifically what to look for and what to avoid, because in this category, the difference between a good product and a poor one is not obvious from the label.

If you’re currently taking fish oil, what follows might change what you buy next time.

Key Takeaways

• Most people are deficient, even those who supplement. The Omega-3 Index, the most reliable blood test for omega-3 status, shows the majority of Australians and Americans sitting well below the optimal range of 8% or above.
• Form matters enormously. Most commercial fish oil is in ethyl ester form, which has 30–50% lower bioavailability than the triglyceride form the body is designed to absorb, meaning many people are getting far less than their label suggests.
• Plant-based omega-3 is not a substitute. The body’s conversion of ALA (found in flaxseed, chia, walnuts) into the active forms EPA and DHA is extremely inefficient, typically less than 10%, and is further impaired by the high omega-6 diets most people eat.
• The omega-6:omega-3 ratio matters as much as intake. The modern Western diet has shifted this ratio from a historical 1–4:1 to 15–20:1, largely due to seed oils, and this imbalance actively crowds out omega-3 at the cellular level.
• Testing before supplementing is the most reliable approach. Without knowing your baseline Omega-3 Index, you may be under-dosing with no measurable effect, or taking more than you need.

What Are Omega-3s? EPA, DHA, and ALA Explained

Before getting into the practical side, it’s worth understanding what omega-3s actually are, because there are a few different types, and they’re not all the same thing.

Omega-3 fatty acids are essential fats, meaning the body cannot make them in meaningful quantities on its own. You have to get them from food or supplements. The three main types are EPA, DHA, and ALA.

EPA (eicosapentaenoic acid)

EPA (eicosapentaenoic acid) is the primary anti-inflammatory omega-3. It’s found in fatty fish and marine sources, and it carries the strongest evidence for cardiovascular health and mood. 

DHA (docosahexaenoic acid)

DHA (docosahexaenoic acid) is the structural omega-3. Your brain, eyes, and nervous system are heavily built from DHA, and it’s critical for brain development in infants and for maintaining cognitive function as we age. 

ALA (alpha-linolenic acid)

ALA (alpha-linolenic acid) is found in plant sources like flaxseed, chia seeds, walnuts, and hemp. The body can technically convert ALA into EPA and DHA, but as covered in more detail below, that conversion is so inefficient it cannot substitute for getting EPA and DHA directly.

When people talk about the health benefits of omega-3, the heart, brain, inflammation, and mood research, they are almost always talking about EPA and DHA from marine sources. That is what the research is based on, and that is what most people are not getting enough of.

Why Most People Are Deficient

The short answer is that the foods we used to get omega-3 from have largely disappeared from the modern diet.

The best dietary sources of EPA and DHA are fatty fish: salmon, mackerel, sardines, anchovies, and herring. To get a meaningful amount of omega-3 from food alone, you’d need to eat two to three serves of fatty fish every week. Most people in Australia and the US eat significantly less than that, and many eat almost none.

It’s not just fish. Traditional animal foods (grass-fed beef, pasture-raised eggs) also contain meaningful amounts of EPA and DHA because those animals are eating what they evolved to eat. When animals are raised on grain, the omega-3 content of their meat and eggs drops substantially. Another casualty of industrialised food production.

The result is that omega-3 deficiency is not a fringe problem, it is the norm in the modern Western diet, and testing consistently confirms this. The Omega-3 Index (the blood test used with clients) measures EPA and DHA as a percentage of red blood cell fatty acids. Optimal is 8% or above. 

Most people in Australia and the US are sitting between 4% and 6%. That gap is significant, and it’s not going to close with one serving of salmon every couple of weeks.

The Omega-6:Omega-3 Ratio: The Hidden Imbalance

There’s another layer to this that most people haven’t encountered. It’s not just about how much omega-3 you’re getting. It’s about the ratio of omega-6 to omega-3 in the diet.

Omega-6 fats are also essential; you need them. They’re found in nuts, seeds, and most vegetable and seed oils. But omega-6 and omega-3 compete for the same metabolic enzymes in the body. 

Think of omega-6 and omega-3 like two teams competing for the same playing field, the same enzymes, the same biological pathways. In a balanced game, both sides get equal time.

But in the modern diet, the omega-6 team has fifteen to twenty players for every one omega-3 player. You can keep adding omega-3 players, but if the opposing team is that large, they’ll still get crowded out.

In pre-industrial diets, the omega-6 to omega-3 ratio was roughly 1:1 to 4:1. In the modern Western diet, it’s estimated to be between 15:1 and 20:1. That is an enormous shift, and it happened in a very short period of time.

The primary driver is seed oils: canola, sunflower, soybean, corn oil, which are extremely high in omega-6. These oils are in almost everything: processed foods, restaurant meals, takeaway, salad dressings, cooking sprays. They replaced saturated fats in the diet from the 1970s onwards, and the ratio shifted dramatically as a result.

This means that addressing omega-3 status involves two levers, not one: increasing omega-3 intake, and reducing the omega-6 dominance by cutting back on seed oils and ultra-processed food. 

The Health Benefits of Omega-3

Cardiovascular Health

This is where the research is deepest. One of the most reliable effects of omega-3 at therapeutic doses is a significant reduction in triglycerides, in the range of 20 to 50%, depending on baseline levels and dose.

As covered in a related article on insulin resistance, elevated triglycerides are a direct marker of metabolic dysfunction, and omega-3 at meaningful doses is one of the most effective nutritional interventions for bringing them down.

EPA in particular has strong evidence for reducing arterial inflammation and improving the health of the arterial lining, the endothelium (the thin layer of cells lining the blood vessels that serves as your first line of defence against atherosclerosis).

In 2019, the REDUCE-IT trial looked at high-dose EPA supplementation of 4 grams per day in people with elevated triglycerides who were already on statins. The trial found a 25% reduction in major cardiovascular events including heart attack and stroke. That’s a substantial benefit from a nutrient, not a drug.

The strongest cardiovascular evidence is in people who already have elevated risk – elevated triglycerides, established heart disease. For younger, healthy people, omega-3 is still genuinely beneficial, but the magnitude of the cardiovascular effect is more modest. It’s one important piece of a comprehensive approach, not a standalone treatment.

Brain Health, Mood, and Mental Health

DHA is the most abundant omega-3 in the brain. It makes up roughly 15 to 20% of the total fatty acid content of the cerebral cortex (the part of the brain responsible for thinking, memory, and decision-making). DHA isn’t just passing through; it is literally a structural building block of brain tissue. Your neurons are partly made of it.

This has significant implications for both development and aging. In pregnancy, DHA is critical for fetal brain and eye development. In older adults, low DHA is consistently associated with accelerated cognitive decline and reduced brain volume. Higher Omega-3 Index levels are associated with better memory and cognitive performance in multiple large population studies.

For mood and mental health, it’s EPA rather than DHA that carries the strongest evidence. 

Multiple meta-analyses, including a 2016 meta-analysis by Mocking et al., have found that EPA supplementation at doses of around 1 to 2 grams per day has clinically meaningful effects on depression, with effects comparable to antidepressants in some studies, particularly in people whose depression has an inflammatory component. 

Given what we know about how widespread low-grade inflammation is, that’s a significant portion of people with depression.

This is also relevant in the context of insulin resistance and its relationship to cognitive decline, what some researchers call Type 3 Diabetes. Adequate DHA helps maintain the structural integrity of neuronal membranes, which is important for the insulin signalling pathways in the brain. These systems are all connected.

Inflammation, Joints, Eyes, and Skin

Chronic low-grade inflammation is the common thread running through most modern chronic disease, and EPA and DHA are two of the most direct dietary tools available for modulating it.

The mechanism is worth understanding briefly. EPA and DHA are converted in the body into a family of molecules called specialised pro-resolving mediators: resolvins, protectins, and maresins. These don’t just suppress inflammation the way anti-inflammatory drugs do; they actively resolve it. 

For joint disease, some of the earliest strong evidence for omega-3 came from rheumatoid arthritis research. Multiple controlled trials show meaningful reductions in morning stiffness, joint tenderness, and the need for anti-inflammatory medications in people supplementing with omega-3. The effect size is clinically relevant, not marginal. 

DHA is also highly concentrated in the retina, and adequate long-term intake is associated with reduced risk of age-related macular degeneration, the leading cause of vision loss in older adults. 

For skin, EPA and DHA support the skin’s lipid barrier, reduce UV-induced inflammation, and are associated with reduced severity of inflammatory conditions like eczema and psoriasis.

Testing: The Omega-3 Index

Before supplementing, it’s worth knowing where you actually stand. There’s a reliable, straightforward test for this: the Omega-3 Index.

The Omega-3 Index measures EPA and DHA as a percentage of your red blood cell fatty acids. Because red blood cells turn over approximately every 120 days, the result reflects your average omega-3 status over the past three to four months. It’s not affected by what you happened to eat yesterday; it’s a stable, meaningful long-term marker.

The target is 8% or above. This is the range where cardiovascular and cognitive protective effects are most consistently demonstrated in research. Most people in Australia and the US are between 4% and 6%. A result below 4% is considered high risk from an omega-3 insufficiency standpoint, and some research has placed it in the same cardiovascular risk category as smoking.

Omega-3 Index	Status
≥ 8%	Optimal. Associated with best cardiovascular and cognitive outcomes.
6–8%	Suboptimal. Supplementation recommended; retest after 3–4 months.
4–6%	Deficient. Very common in Western populations. Meaningful supplementation needed.
< 4%	High risk. Urgent attention required; higher therapeutic doses indicated.

In Australia, Nutripath offers a comprehensive fatty acid panel that includes the Omega-3 Index. In the US, Vibrant Wellness and Diagnostic Solutions both offer detailed omega-3 testing, and OmegaQuant is available directly to consumers without a practitioner. Each of these gives a clear Omega-3 Index result that tells you exactly where you stand.

The reason testing matters more than guessing is straightforward: without knowing your baseline, you might be under-dosing and making no meaningful change, or you might be taking more than you need. 

Testing also lets you recheck after three to four months of supplementation to confirm your levels have actually moved into the target range. Some people need significantly more than others, and testing is the only reliable way to find that out.

Fish Oil vs Krill vs Algal vs Cod Liver Oil

Not all omega-3 supplements are the same, and the form you choose matters.

Fish oil

Fish oil is the most widely available and most researched form. It’s derived from oily fish (typically anchovy, sardine, mackerel, or herring) and it contains both EPA and DHA. Fish oil is a solid foundation, but quality varies enormously, and as covered in the next section, the molecular form matters a great deal.

Krill oil

Krill oil comes from Antarctic krill – tiny crustaceans very low on the food chain. The EPA and DHA in krill oil are in phospholipid form, which may improve how they cross cell membranes, including the blood-brain barrier. Krill oil also naturally contains astaxanthin, a potent antioxidant that helps protect the oil from going rancid. 

The downside is that krill oil contains less EPA and DHA per capsule than concentrated fish oil, so you typically need more of it to reach the same dose, which makes it more expensive per effective gram. It’s a good option, particularly for brain health.

Algal oil

Algal oil is worth highlighting specifically, because this is the original source. Fish accumulate omega-3 by eating algae. Algal oil goes straight to that source: it provides genuine EPA and DHA directly, is fully vegan, carries no risk of heavy metal contamination from fish, and has no fishy taste. 

For anyone who doesn’t consume fish, or who prefers a plant-based supplement, algal oil is the best choice. Not flaxseed oil, not chia oil. Algal oil.

Cod liver oil

Cod liver oil is a traditional supplement that provides EPA and DHA plus naturally occurring vitamins A and D. The vitamin D content is a genuine bonus. However, the vitamin A content is something to be aware of, particularly for pregnant women, where excessive preformed vitamin A is not recommended. 

Cod liver oil also typically has lower EPA and DHA concentrations per teaspoon compared to concentrated fish oil, so it’s better suited to general maintenance than to correcting a significant deficiency.

The Critical Quality Issue: Triglyceride vs Ethyl Ester Form

This is the most important thing in this entire article – and it’s something the supplement industry has made very easy not to know.

Fish oil naturally exists in what’s called triglyceride form. That is how omega-3 exists in fish tissue, and it is the form the body is designed to absorb and use. 

When fish oil is manufactured and concentrated (to achieve the high EPA and DHA numbers on the label) it typically goes through a process that converts it into what’s called ethyl ester form. The fatty acids get attached to an ethanol molecule instead of a glycerol backbone. It’s a cheaper manufacturing shortcut that allows higher concentrations to be achieved more easily.

The problem is that ethyl ester fish oil has approximately 30 to 50% lower bioavailability than triglyceride form. Some research puts the gap even higher, particularly when it’s taken without a fat-containing meal.

Ethyl ester is not how omega-3 exists naturally in any food. The body has to perform an extra conversion step before it can even use it, and a significant amount is lost in that process.

Here’s the practical consequence: two products on a pharmacy shelf can both say “1,000mg of EPA+DHA” on the label – one in triglyceride form, one in ethyl ester form. They look identical. But one is delivering significantly more omega-3 to your cells than the other.

How to tell the difference: look at the label. If it says “triglyceride form”, “TG form”, or “re-esterified triglyceride”, that’s what you want. If it says “ethyl ester” or “EE”, avoid it. And if it doesn’t say anything at all about the form, which is most products, it is almost certainly ethyl ester, because manufacturers who use triglyceride form tend to advertise that fact.

This is the single most common reason clients who have been taking fish oil for years still show a low Omega-3 Index when tested. They weren’t taking a useless product, but they were absorbing significantly less than they thought.

Plant-Based Omega-3: Why ALA Isn’t Enough

A common assumption is that eating flaxseed, chia seeds, or walnuts provides adequate omega-3. These foods contain ALA (alpha-linolenic acid), which is the plant form of omega-3. ALA is a real omega-3.

But it’s a precursor, not the active form. The body has to convert ALA into EPA and DHA before it can use it for all the things the research is based on.

Think of ALA as a raw ingredient, and EPA and DHA as the finished products your body actually needs. Your body can manufacture the finished products from that raw ingredient, but the production process is slow, inefficient, and easily disrupted.

It’s far more reliable to get the finished products directly. Relying on ALA alone is a bit like trying to run a restaurant entirely on raw ingredients you have to process yourself, when the finished product is available right next door.

The conversion rate is very poor. On average, the body converts about 5 to 10% of ALA into EPA, and less than 4% into DHA. And those are the optimistic figures. A high omega-6 intake, which is almost universal in the modern diet, directly competes with the same conversion enzymes.

Some people have genetic variants that reduce their conversion capacity further. Certain nutrient deficiencies, including zinc, can impair the process as well.

For anyone on a strictly plant-based diet, the answer is not more flaxseed. The answer is algae oil – which provides EPA and DHA directly, without conversion. It’s vegan, it’s clean, and it works.

What to Avoid: Rancidity, Labels, and Red Flags

Beyond the ethyl ester issue, there are a few other important things to check.

Rancidity and oxidation

Omega-3 fatty acids are highly susceptible to oxidation. Once a fish oil has oxidised, it doesn’t just lose its benefit – the oxidised compounds may actually cause harm, contributing to the oxidative stress they were supposed to reduce.

Studies testing commercially available fish oils have found that a significant proportion exceed recommended oxidation limits. This isn’t a niche problem with obscure brands; it applies across the market, including well-known names.

How to check: open a capsule and smell it. Fresh, high-quality fish oil should have a mild, clean, slightly marine smell. If it smells strongly fishy, rancid, or has an acrid or “paint-like” odour – it has oxidised. You can also bite a capsule open and taste it. A good fish oil should taste mild and clean. Strong, bitter, or “old fish” flavour is a sign of rancidity. 

Underdosing

This is one of the most widespread problems. Most standard fish oil capsules contain somewhere between 300 and 500mg of EPA and DHA combined.

If you’re taking one of these per day, you’re getting a third to a half of the dose needed even for general maintenance. Two capsules of a low-concentration product still isn’t a therapeutic dose.

The label trap

Many products state the total fish oil content on the front of the label – “1,000mg fish oil” – rather than the EPA and DHA content. 1,000mg of fish oil might contain only 300mg of EPA and DHA combined. Always turn the bottle over and look at the actual EPA and DHA milligrams per serving. That is the number that matters.

What to Look For: Quality Brands

To summarise the key quality criteria before looking at specific brands: triglyceride or re-esterified triglyceride form; actual EPA and DHA milligrams clearly stated; third-party testing and certification for purity and freshness; sourced from small fish species (anchovy, sardine, herring); and ideally some freshness protection in the packaging – nitrogen-flushed capsules, opaque bottles, and a clear best-before date.

The certification to look for is IFOS (International Fish Oil Standards) 5-star rating, which independently verifies freshness, potency, and purity.

Internationally available brands that consistently meet these standards include:

Nordic Naturals – probably the most widely known quality omega-3 brand globally. Their Ultimate Omega and Pro Omega ranges use triglyceride form, are IFOS certified, and have excellent freshness standards.

Carlson Labs – a long-established brand with a strong track record for freshness and quality. Their Norwegian Omega-3 Gems use triglyceride form and are regularly awarded for freshness testing.

Australian practitioner-grade brands include:

• Metagenics (OmegaGenics range) – triglyceride form, practitioner-grade, high purity standards. 
• Bioceuticals (UltraClean EPA/DHA Plus) – a well-formulated, triglyceride-form product 
• Orthoplex – also high quality and triglyceride form. 

Contact us if you are in Australia and want access to the Australian brands.

For vegan patients in any region: look for algal oil products providing at least 500mg combined EPA+DHA per serving. Nordic Naturals Algae Omega is a well-regarded option.

These are examples of the quality standard to look for – there are other good products available. The criteria matter more than the specific brand. Use the label checks described above, verify the form, and check for IFOS certification.

Dosing Guide: Maintenance to Therapeutic

The honest answer to “how much should I take?” is that it depends on your Omega-3 Index. Testing first is always the most personalised approach. But here is a practical guide:

For general maintenance – if your index is in the 6 to 8% range – 1 to 2 grams of combined EPA and DHA per day is a reasonable target. This maintains levels and provides ongoing anti-inflammatory and cardiovascular support.

For correcting a deficiency – if your index is below 6% – 2 to 3 grams of EPA and DHA per day is typically recommended. Retest after three to four months to see how much the index has moved.

For therapeutic purposes – elevated triglycerides, significant inflammatory conditions, mood support, cardiovascular risk reduction – the clinical evidence often uses doses of 2 to 4 grams per day of EPA and DHA. At these doses, you’re approaching what was used in the REDUCE-IT trial.

For depression and mood specifically, the evidence points to EPA rather than total omega-3. Look for a high-EPA product – one where EPA makes up at least 60% of the omega-3 content – and aim for 1 to 2 grams of EPA daily.

In pregnancy, DHA is the priority for foetal brain development. A minimum of 200mg of DHA daily is commonly recommended, but at least 1 gram of combined EPA and DHA during pregnancy is a reasonable target for most women. Algal oil is an excellent option during pregnancy as it avoids any contamination concerns and the vitamin A issue associated with cod liver oil.

One practical note: always take omega-3 supplements with a meal that contains some fat – this significantly improves absorption, particularly for ethyl ester products. For triglyceride-form products, the meal requirement is less critical but still helpful.

Safety note: omega-3 has mild blood-thinning properties. At doses above 3 grams per day, it’s worth mentioning to your doctor if you’re on anticoagulant medication – warfarin, apixaban, aspirin. The effect is modest, but worth transparency with whoever is managing your medications.

A Practical 6-Step Action Plan

Step 1: Get Tested

Don’t guess. In Australia, Nutripath offers the Omega-3 Index as part of a fatty acid panel. In the US, Vibrant Wellness and Diagnostic Solutions both offer detailed omega-3 testing, and OmegaQuant is available directly to consumers. Knowing your number is the starting point for everything else.

Step 2: Check What You’re Currently Taking

If you’re already supplementing, pick up the bottle and look at the label. Find the actual EPA and DHA milligrams. Look for whether it specifies triglyceride or re-esterified form. If it doesn’t say – assume ethyl ester. Open a capsule and smell it. Fresh oil should smell clean and mild, not strongly fishy.

Step 3: Upgrade Your Supplement if Needed

If you’re currently on an ethyl ester product or a low-dose supplement, consider switching to a triglyceride-form product with clearly stated EPA and DHA at a meaningful dose. The brands mentioned above – Nordic Naturals, Carlson, Thorne internationally; Metagenics, Bioceuticals, Orthoplex in Australia are good reference points for the quality standard.

Step 4: Eat More Fatty Fish

Two to three serves per week of salmon, mackerel, sardines, anchovies, or herring. Supplementation and food sources work together, they’re not substitutes for each other.

Step 5: Reduce Seed Oils

Canola, sunflower, soybean, and corn oil, reducing these improves your omega-6 to omega-3 ratio independently of how much omega-3 you add. Shift toward olive oil, avocado oil, and butter or ghee for cooking.

Step 6: Retest in Three to Four Months

Once you’re supplementing consistently at the right dose in the right form, retest the Omega-3 Index to confirm it’s moved toward 8% or above. If it hasn’t moved enough, increase the dose slightly and recheck.

Omega-3 is one of those nutrients where the gap between doing it poorly and doing it well makes an enormous difference. The same money spent on a high-quality, triglyceride-form product with a meaningful dose will deliver far more to your cells than three times as much spent on a cheap ethyl ester capsule. Know your number.

To learn more about testing your omega-3 levels, visit Omega-3 Index testing or contact us here to discuss what’s right for your situation.

Frequently Asked Questions

References

• REDUCE-IT trial (high-dose EPA and cardiovascular events) – Bhatt et al., 2019
• Omega-3 supplementation and major depressive disorder – Mocking et al., 2016