The ultimate guide to omega-3, omega-6 and fish oil

The Ultimate Guide to Omega-3, Omega-6 and Fish oil

Why are fish oil supplements so popular?

In recent times, fish oil supplements have gained significant popularity amongst consumers hoping to reduce their risk of cardiovascular disease, including coronary heart disease and stroke. This reflects a shift from previous use of fish oil in the 19th century which centred around the use of cod liver oil primarily as a source of vitamin D to help prevent Rickett's in children living in sun-deprived parts of Europe.

What is fish oil and why is it important?

Conventional fish oil supplements are derived from fatty fish like tuna and mackerel. Cod Liver Oil on the other hand, is derived from the livers of Cod and is mainly used owing to its rich vitamin A and D content, in addition to omega-3. Fish oil has gained increasing popularity due to its rich omega-3 content. Omega-3s obtained from fish include the omega-3 polyunsaturated fatty acids: docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and docosapentaenoic acid (DPA). Fish oil supplements are typically rich in DHA and EPA, and contain lesser amounts of DPA. DHA and EPA have been found to be particularly important for cardiovascular health.

What's better - fish or supplements?

Many people find it hard to consume fish on three days each week, owing to multiple factors including dietary preferences and cost. Supplements provide an alternate source of omega-3 for people who don't either don't eat fish at all, or who may not meet the Heart Foundation recommendation of three serves per week.

However, generally speaking, there's no good substitute for a nutrient rich healthy diet. A heart-healthy diet should contain an abundance of vegetables, fruits, wholegrains, lean meats and fish, nuts and seeds, and limit saturated fats and salt. A diet containing fatty fish like salmon, mackerel, tuna and sardines on three days each week would provide up to 500mg of marine-sourced omega-3 per day, which would be in keeping with the Australia's Heart Foundation recommendations.

Omega-3 vs Omega-6… What’s the difference? Is omega-6 bad for you?

Omega-3 is primarily sourced from fatty fish as well as plant sources like walnuts and has been widely recognised for its proposed cardiovascular benefits and anti-inflammatory effects. Omega-6 is found in vegetable oils as well as walnuts, tofu, sunflower seeds, eggs, almonds and cashews. Both are essential fatty acids that must be sourced from the diet and both play important roles in human health.

Omega-6 has obtained a relatively poor reputation in recent times, due to evidence suggesting that diets higher in omega-6 and lower in omega-3 promote inflammation and are associated with higher rates of cardiovascular disease, cancer, and autoimmune disease. What’s confusing is that omega-6 is an essential part of the human diet and plays an important role in lowering harmful LDL-cholesterol and boosting good cholesterol known as HDL. Despite these known benefits of omega-6, there have been widely publicised concerns over the body’s ability to convert the most common form of omega-6, known as linolenic acid into arachidonic acid, which is a precursor to molecules that can promote inflammation and blood clotting in the body. However, rather than cutting back on essential omega-6, most evidence suggests that we should aim to continue healthy intakes of omega-6 and boost our intake of omega-3 fatty acids, with the overall effect of decreasing the omega-6 to omega-3 ratio.

The omega-6 to omega-3 ratio has become a major topic for discussion amongst scientists and health experts in recent times. Several scientific sources estimate that humans evolved from a diet consisting of an omega-6 to omega-3 ratio of approximately 1:1, whereas conventional western diets tend to reflect a ratio of 15:1 omega-6 to omega-3. Evidence suggests that diets with such high ratios of omega-6 to omega-3 are associated with higher rates of pro-inflammatory conditions like cardiovascular disease. This association is further enforced by the fact that cardiovascular disease is now the leading cause of death in western society.

However, a recent 2019 publication by Harvard Health explains that omega-6 and omega-3 are both important for human health, and that rather than cutting down on omega-6 people should aim to increase consumption of omega-3 in order to help lower the omega-6 to omega-3 ratio and promote optimal health outcomes. Some studies have shown that for people with cardiovascular disease maintaining an omega-6 to omega-3 ratio of 4:1 is associated a 70% reduction in mortality. While the optimal ratio of omega-6 to omega-3 remains a subject of debate, the bulk of the evidence suggests that we should aim for healthy intakes of both omega-6 and omega-3, and be conscious of boosting intakes of omega-3, rather than cutting down on healthy sources of omega-6.

In summary, omega-6 and omega-3 are both important for human health. Rather than cutting out food rich in omega-6, people should focus on increasing diets rich in omega-3, particularly oily fish.

What evidence is there to support the use of fish oil and Omega-3 for cardiovascular disease risk reduction?

Our bodies are not capable of synthesising Omega-3 and we are therefore completely dependent on sourcing omega-3 from our diet. Fish has been recognised as the most important source of omega-3 fatty acids. Scientific evidence has consistently found strong associations between high intakes of fish and lower rates of cardiovascular disease, including heart failure, sudden cardiac death, and stroke. 

In addition to the association between higher intake of marine-sourced Omega-3 and lower rates of cardiovascular disease, omega-3 supplements containing EPA and DHA have been found to help lower triglyceride levels (unhealthy dietary fats). High levels of triglycerides may contribute to hardening of the arteries known as atherosclerosis which increases the risk of heart attack and stroke. This is the basis for health professionals recommending fish oil for people with high blood triglyceride levels, with the aim of reducing their risk of cardiovascular disease.

A large review article published in the peer reviewed journal ‘Heart, Lung and Circulation’ in 2015, included data from two systematic reviews and meta-analyses, three Randomised Controlled Trials (RCTs) and six prospective cohort studies. The review summarises the evidence for omega-3 in the prevention and treatment of cardiovascular disease and forms the basis for current Heart Foundation recommendations regarding omega-3. The authors concluded that higher intakes of fish were associated with lower rates of stroke, sudden cardiac death, heart attacks, and heart failure. Evidence was also found to support the use of omega-3 supplements for treatment of high triglyceride levels, and modest positive benefits were found for people suffering from heart failure. While higher intakes of omega-3 in the diet were found to be protective for prevention of coronary heart disease, there was a lack of evidence to suggest a benefit in those who have already developed significant coronary heart disease in order to prevent it from getting worse.

What are the Australian Heart Foundation recommendations regarding Fish Oil and Omega-3?

The current Heart Foundation recommendations were updated based on their 2015 review of the ‘most up-to-date and credible scientific evidence’ taking into account the results of the above review article published in 2015.

These guidelines recommend omega-3 sourced from fish as the most important source of omega-3 for heart health. Specifically, they recommend having two to three serves of fish (particularly oily fish) per week in order to provide an average intake of 250 to 500mg of marine-sourced omega-3 per day (containing primarily EPA and DHA). Supplements are recommended for those who do not eat fish, or who do not meet the recommended intake for two to three serves per week.

In addition, omega-3 supplements like fish oil are often recommended for the purposes of lowering blood triglyceride levels or in conjunction with other treatments to improve outcomes for people with heart failure. 

Finally, the Heart Foundation also recommends a diet containing plant-sourced omega-3 (ALA) at a dose of 1 gram per day.

What Omega-3 options are available to Vegans and those who prefer to avoid fish-sourced Omega-3?

Vegan diets are growing in popularity in Australia and other parts of the world for many reasons, including trends towards eco-sustainability; reduction in animal-cruelty; and preferences regarding health and diet. Some people who don’t necessarily follow a vegan diet may also prefer non-animal sourced options to help reduce their carbon footprint and their personal impact on animal hunting and farming.

The options for non-animal sourced omega-3 containing EPA and DHA (which are the primary omega-3 types sourced from fish), differ from the usual plant sources of omega-3 which contain ALA. As outlined above, marine-sources of omega-3 like EPA and DHA have the most evidence for cardiovascular risk protection, but plant sources like ALA are also recommended as part of a balanced heart-healthy diet.

ALA is abundant in plant-sourced foods including walnuts, hemp seeds, chia seeds, flaxseed, and canola and soybean oils. Incorporating these foods into the diet can assist in achieving the Heart Foundation recommendation of 1 gram of ALA per day. ALA can be converted into EPA and DHA, but the process of conversion is not very efficient, so intake of these foods will not achieve the target intake of EPA and DHA.

Luckily, some vegan-friendly modern supplements are available that contain EPA and DHA replicating the types of omega-3 found in fish and fish oil supplements. While these supplements have not necessarily been verified directly in terms of their ability to confer cardiovascular risk protection, studies have shown that the bioavailability and absorption characteristics of EPA and DHA derived from vegan-friendly supplements containing algae oil are comparable to the forms derived from fish. Furthermore, we know that fish obtain their omega-3 from eating algae themselves, so the types of omega-3 obtained from algal sources are likely to be similar to omega-3 obtained from fish.

Algae oil and algae-sourced omega-3 supplements are therefore important considerations for people looking for alternatives to fish oil for sources of important forms of omega-3 like EPA and DHA that have been shown to confer significant cardiovascular protective benefits. There are several vegan-friendly supplements available on the market, containing various amounts of EPA and DHA. While algae oil can be bought as cooking oil, cooking with algae oil will not provide any omega-3 benefits. Omega-3s are not heat stable and will be destroyed in the cooking process. It is important to look for vegan-friendly supplements that contain EPA and DHA and the overall amounts contained in each dose.

The bottom line:

  • Both omega-3 and omega-6 play important roles in human health.
  • Conventional western diets tend to include at least 10 times more omega-6 than omega-3, which may not be optimal for health outcomes.
  • In general, most people should aim to increase the amount of omega-3 in the diet by incorporating omega-3 sources which can be obtained from oily fish or supplements.
  • Scientific evidence has consistently found strong associations between high intakes of fish and lower rates of cardiovascular disease, including heart failure, sudden cardiac death, and stroke.
  • The benefits of fish on cardiovascular health outcomes are attributed to the omega-3 content, particularly DHA and EPA.
  • DHA and EPA (abundant in fish oil) are the most important dietary types of omega-3 which have been linked to cardiovascular disease prevention and lowering of triglycerides. Triglycerides are unhealthy dietary fats, high levels of which can contribute to atherosclerosis.
  • The Heart Foundation recommends having two to three serves of oily fish per week for optimal cardiovascular health. For those that cannot meet the recommended amount, supplements containing omega-3 may be useful.
  • Algae-based supplements are rich in omega-3 and are therefore important sources of omega-3 for people who prefer to avoid fish or fish-sourced supplements. Fish obtain their omega-3 content from consumption of algae so its conceivable that omega-3 obtained from algae is likely to be a trusted source of DHA and EPA and a reasonable alternative to fish for those who prefer plant-sourced omega-3.
  • The heart foundation recommends taking 250 to 500mg of marine-sourced omega-3 per day (containing primarily EPA and DHA) as well as 1 gram of ALA per day.
  • ALA is a type of omega-3 and can be sourced from supplements or plant foods including walnuts, hemp seeds, chia seeds, flaxseed, and canola and soybean oils.


Fish and omega-3: Questions and answers. Heart Foundation Australia. Available from:

Nestel et al. 2015. Indications for Omega-3 Long Chain Polyunsaturated Fatty Acid in the Prevention and Treatment of Cardiovascular Disease. Heart, lung and circulation. Available from:

Rachael L. 2017. Healthline. Available from: