Omega-3 and omega-6 are both essential fats.
The term ‘essential’ means that the human body cannot make these fats, so we need to acquire them from our diet.
Over recent decades, several researchers have hypothesized that the omega-6 to 3 ratio of the human diet might play a key role in health and disease risk (1, 2).
However, evidence suggests that the dietary omega-6 to 3 ratio itself is probably not the issue. A recent critical appraisal even noted that the omega-6 to 3 ratio “has become scientifically outdated” (3).
This article discusses whether the omega-6 to 3 ratio of the human diet matters and the most important considerations.
What Is the Omega-6 to 3 Ratio?
If you have six apples and one orange, the ratio of apples to oranges is six to one (or 6:1).
Likewise, the same rules apply when calculating the omega-6 to 3 ratio. If one consumes 10 grams of omega-6 and 0.5 grams of omega-3, then the ratio is 20:1.
In other words: the omega-6 to 3 ratio refers to the amount of omega-6 we consume compared to omega-3.
Both of these fats have different functions within the body.
As a simple example, the main dietary omega-6 fatty acid (linoleic acid) is a precursor to arachidonic acid, which plays a role in pro-inflammatory and anti-inflammatory processes. On the other hand, omega-3 fatty acids, such as eicosapentaenoic acid (EPA), have well-documented (and quite powerful) anti-inflammatory properties (4, 5).
The Omega-6 to Omega-3 Ratio Has Changed Within Human Diets – But Does It Matter?
According to some researchers, humans evolved on a diet that provided omega-6 and omega-3 at a relative ratio of around 1:1. However, estimates based on current dietary trends now place this ratio anywhere between 15 to 1 and 20 to 1 (1).
The reason for much of this change is how humans eat.
As people have started to eat less seafood and fewer whole foods, omega-3 intake has fallen. Also, our intake of omega-6 has risen rapidly, mainly due to vegetable oil intake.
- In 1909: soybean oil (primarily a source of omega-6) provided 0.006% of calories in the average American diet.
- By 1999: soybean oil contributed more than 7% of total calories. Surprisingly, this represents a 1000-fold increase in consumption (6).
Meat, poultry, and nuts can also be substantial sources of omega-6, particularly when consumed in large quantities.
As previously stated, some people argue that we have an imbalanced dietary ratio of omega-6 to omega-3 that may have negative connotations for human health (1, 2).
But does the latest evidence support this assertion or is there more to it?
A Higher Omega-3 Index (and Increased EPA/DHA Intake) Improves Heart Health
First of all, it is important to note that blood levels of omega-3 are quite consistently associated with improved cardiovascular outcomes.
The omega-3 index is a clinical measurement that establishes (7, 8):
- The amount of omega-3 (EPA/DHA) in the blood.
- The proportion of EPA and DHA in the blood compared to all other fatty acids.
- The ratio of EPA to AA (an omega-6 fatty acid).
For those unaware of any of these abbreviations, EPA stands for eicosapentaenoic acid, a highly bioavailable form of omega-3 found within seafood. The same is true for DHA, which is an abbreviation of docosahexaenoic acid (9).
On the other hand, arachidonic acid (ARA) is an omega-6 fatty acid synthesized in the body from linoleic acid. Linoleic acid is the primary omega-6 fatty acid found within nuts, seeds, and vegetable oils (10).
Research demonstrates that a higher omega-3 index has beneficial effects on human health. Notably, a higher EPA to ARA ratio in the blood appears to lower the risk of cardiovascular disease and cardiovascular events (11, 12, 13).
Furthermore, a comprehensive meta-analysis analyzed 19 observational studies involving more than 45,000 participants. This meta-analysis showed that the risk of fatal coronary heart disease fell in a consistent linear pattern when comparing participants with higher blood levels of EPA and DHA to lower levels (14).
Increasing Dietary EPA/DHA Intake Has Various Benefits
Data also shows that increasing our dietary intake of EPA and DHA may benefit various markers associated with cardiovascular risk.
- A recent systematic review of randomized controlled trials demonstrated that higher intake of EPA and DHA improved several risk markers for cardiovascular disease. These improvements included lower triglycerides, larger LDL particle size, and higher HDL levels. Additionally, larger intakes of EPA alone lowered LDL levels (15).
- A meta-analysis of 171 randomized clinical trials highlighted that EPA/DHA supplementation reduced risk factors for cardiovascular disease risk by lowering cholesterol, inflammation, and blood pressure (16).
- Numerous clinical intervention trials show that increasing EPA/DHA intake lowers oxidative stress and reduces pro-inflammatory gene expression (17, 18, 19, 20, 21).
Does a High Dietary Omega-6 To Omega-3 Ratio Have An Adverse Effect?
Now that we have established the benefits of a higher omega-3 index, it’s time to assess the importance of the relative amounts of omega-6 and omega-3 we consume.
Does a high dietary omega-6 to omega-3 ratio negatively influence the omega-3 index?
First, as discussed, it is clear that higher tissue levels of omega-3 to omega-6 (e.g. the ratio of EPA to ARA) are beneficial.
However, evidence suggests that the absolute amount of omega-6 compared to omega-3 in the diet is probably not the main issue. Instead, the issue appears to be more about an omega-3 deficiency.
Let’s now look at some reasons why.
The Claim That Omega-6 Is Inflammatory
One of the main reasons people have historically touted the omega-6 to omega-3 ratio is the claim that omega-6 fatty acids are inherently inflammatory. However, this claim is overly simplistic and lacks understanding of the metabolism of omega-6 fatty acids and their effect on the body.
The original idea that omega-6 fatty acids are inflammatory largely stems from the following research findings:
- Arachidonic acid (ARA) can be synthesized from linoleic acid, the main omega-6 fatty acid found in food. ARA can be converted into pro-inflammatory eicosanoids, signaling molecules used within the body (22, 23).
- Using aspirin can block the conversion of ARA into these pro-inflammatory eicosanoids (24).
- Omega-3 eicosapentaenoic acid (EPA) and ARA compete with each other as substrates (materials) for the activation of enzymes in control of inflammation (25).
- Alpha linoleic acid (an omega-3 found in plants) and linoleic acid also compete for conversion into EPA or ARA (26).
In other words, the omega-6 to 3 dietary ratio beliefs cover the idea that “good” anti-inflammatory omega-3 and “bad” pro-inflammatory omega-6 are in constant competition.
This is an overly simplistic (and incorrect) view.
Dietary Omega-6 Is Not Inflammatory
Firstly, it is true that arachidonic acid can be converted into a range of eicosanoids (signaling molecules). But while some of these are pro-inflammatory, others have anti-inflammatory functions (27, 28).
Secondly, the amount of EPA/DHA to ARA in the cells influences inflammatory processes rather than omega-6 to omega-3 in the diet.
On this note, a higher intake of linoleic acid (omega-6 from oils, nuts, meat, etc) does not lead to significant increases in arachidonic acid. For example, research has shown that tissue levels of arachidonic acid stop responding to increased dietary linoleic acid when the amount is above 2% of total energy (29).
Furthermore, a systematic review of human trials demonstrated that high linoleic acid intakes on typical Western diets does not raise tissue levels of arachidonic acid (30).
Some further significant research findings that dispel the idea that dietary omega-6 is inflammatory:
- A systematic review of fifteen randomized controlled trials found no evidence that increased dietary linoleic acid intake leads to increased inflammatory markers (31).
- Blood markers of inflammation were not significantly affected by increased linoleic acid intake in a systematic review and meta-analysis of more than 30 clinical human trials (32).
- In a systematic review and meta-analysis of large observational trials, involving more than 310,000 participants, greater linoleic acid intake was associated with reduced risk of cardiovascular disease in a dose-response manner (33).
Do Omega-6 and Omega-3 Compete For Cellular Uptake?
Do the omega-3 and omega-6 we consume compete with each other for uptake and absorption?
Yes and no.
The three most common forms of omega-3 are:
- Eicosapentaenoic acid (EPA): primarily found in seafood and other marine sources. DHA is already in a bioavailable form that the human body can use.
- Docosahexaenoic acid (DHA): again, mainly found in seafood. DHA is a bioavailable form of omega-3 too.
- Alpha-linolenic acid (ALA): this is a form of omega-3 found within plant foods such as nuts, seeds, and some vegetable oils. The body must convert ALA into DHA and EPA to be able to use it.
The ALA form of omega-3 and the omega-6 linoleic acid indeed compete with each other for conversion to their bioavailable forms. Thus, consuming large amounts of omega-6 and relatively small ALA amounts will lower the amount of ALA that the human body can absorb (34).
However, the same is not true for EPA/DHA. Higher amounts of linoleic acid in the diet do not affect the amount of omega-3 we can absorb from EPA and DHA.
Furthermore, omega-3 from preformed EPA and DHA sources (like oily fish) are extremely bioavailable, but ALA already has meager absorption rates. Based on trials in healthy human participants, the amount of ALA that the human body can convert to EPA may be as low as 8% and for DHA, only 0-4% (35).
This really emphasizes the importance of consuming sufficient amounts of preformed omega-3.
The Real Issue: Getting Sufficient EPA/DHA Is More Important Than the Omega-6 to 3 Dietary Ratio
As we have seen thus far, increasing dietary linoleic acid intake does not significantly increase inflammatory markers, and it has relatively little effect on tissue levels of arachidonic acid.
So, what does have an effect?
The answer to that question is pre-formed omega-3. Increasing the amount of preformed omega-3 (EPA/DHA) we consume has several effects:
- Omega-3 from EPA/DHA reliably raises the omega-3 index, and the amount of omega-3 in our cells (36).
- Increasing the amount of EPA/DHA in tissue also lowers tissue levels of arachidonic acid, thus improving the ratio of EPA to ARA (37).
Thus, ensuring sufficient intake of omega-3 from EPA and DHA is the main issue rather than the total amount of omega-3 and omega-6 in our diet.
Yet Most People Don’t Consume Enough EPA and DHA
Unfortunately, the vast majority of people do not consume enough EPA and DHA.
A recent global survey analyzed the amount of EPA and DHA in the bloodstream among adults all over the world (38).
Although certain regions, such as Japan and Scandinavia, had high blood levels of EPA and DHA, most of the world did not.
In Japan, the percentage of EPA and DHA as a fraction of total fatty acids was very high (>8%). Yet, it was very low (<4%) in the Americas, Europe, the Middle East, Southeast Asia, and Africa.
One of the key reasons for this low intake is the lack of dietary omega-3 from seafood sources. For instance, data shows that US adults only consume an average of 0.43 ounces of fish, of which only 0.07 ounces is from oily fish, per day (39).
How Can We Get More EPA and DHA Omega-3 From Our Diet?
The best and most reliable way to get more EPA and DHA from food is to increase our oily fish consumption.
For a helping hand in this area, here are some of the most omega-3-rich fish options.
Fish oil supplements that provide decent amounts of EPA/DHA are also good options for those that don’t like fish.
Most health organizations tend to recommend consuming at least 250-500 mg EPA and DHA per day:
- The American Dietary Guidelines recommend at least 250 mg (40).
- The American Heart Association recommends at least 1 gram for patients with existing heart disease (41).
However, some countries advise consuming much higher amounts. This resource shows the global recommendations for EPA and DHA from different countries around the world.
Considerations For Vegans and Vegetarians
It can be difficult to find sources of EPA and DHA on a vegan diet.
However, microalgae supplements (known as algal oil) are a vegan-friendly source of preformed EPA and DHA (42).
As with fish oil supplements, look for a product that contains a good amount of EPA and DHA.
That said, research has shown that the actual amount of EPA and DHA in omega-3 supplements can often differ from the label claims (43).
As a result, it is important to choose a reputable brand: the website Labdoor provides a guide to popular fish oil and vegan omega-3 supplements. This analysis covers whether or not the supplements meet their label claims and their degree of heavy metal contamination, so it is a good way of checking how reputable a specific supplement is.
As covered in this article, here is a summary of the main take-home points:
- Omega-3 fatty acids are essential, and we need to obtain them from our diet.
- EPA and DHA are much more bioavailable than ALA.
- The tissue ratio of omega-3 (EPA/DHA) to arachidonic acid (ARA) is important, but the exact ratio of omega-6 to omega-3 in the diet is less important.
- The dietary ratio of omega-6 to omega-3 has some influence, particularly when the only dietary source of omega-3 is ALA. But the evidence firmly shows that absolute intake of preformed omega-3 plays a much more significant role than this ratio.
- There is a lack of evidence for linoleic acid being inflammatory or significantly increasing tissue omega-6 levels.
- Getting enough DHA and EPA has a much more significant impact on omega-3 tissue levels and health outcomes.