Omega-6 to Omega-3 Ratio and Arachidonic Acid: What the Test Reflects

Written by Dr. Ryan Kneessi, ND

Quick answer: The omega-6 to omega-3 ratio, or the related arachidonic acid to EPA ratio, compares two families of fats in the blood or in red blood cell membranes. A higher ratio usually reflects low omega-3 intake, and a lower EPA-to-arachidonic acid balance has been linked with more coronary heart disease in people with higher inflammation. Higher linoleic acid, the main omega-6 fat, has not been linked with more heart disease in large pooled studies.

Fatty acid panels often report more than the Omega-3 Index. Many also show omega-6 fats such as linoleic acid and arachidonic acid, and then a ratio, either total omega-6 to omega-3 or arachidonic acid to EPA, usually shortened to the AA-to-EPA ratio. These ratios are popular because they seem to sum up the balance between fats that are often described as inflammatory and fats that are often described as calming. As you will see, the research is more nuanced than that simple story, and I think it is worth understanding before reading too much into one number. My separate article on the Omega-3 Index covers EPA and DHA on their own.

This article is educational. It explains what the marker reflects and how researchers connect it to the deeper mechanisms of aging, so you can have a more informed conversation with your own provider.

What does the omega-6 to omega-3 ratio measure?

Most fatty acid tests measure the fats built into the membranes of red blood cells, which reflect intake over the previous few months, and some measure plasma or serum fats, which change faster. Linoleic acid is the main omega-6 fat in food, found in nuts, seeds and many vegetable oils, and the body converts a small part of it into arachidonic acid, which is also found in meat, eggs and poultry. The main omega-3 fats are EPA and DHA from fish and seafood, along with alpha-linolenic acid from plants such as flax and walnuts.

The total omega-6 to omega-3 ratio compares all of the omega-6 fats with all of the omega-3 fats, while the AA-to-EPA ratio compares arachidonic acid with EPA specifically. A higher ratio means relatively more omega-6 or less omega-3 in the membranes. In practice, the ratio is usually high because omega-3 is low rather than because omega-6 is unusually high, which is why it so often moves together with the Omega-3 Index. Fish oil use, seafood intake, the type of cooking oils someone uses, genetics that affect how fats are converted and the timing of the test all shape the result.

How is this ratio connected to aging and root causes?

Arachidonic acid and EPA compete for the same enzymes, and each is turned into signaling molecules called eicosanoids. Many of the molecules made from arachidonic acid help start inflammation and blood clotting, which the body needs for healing, while EPA and DHA give rise to compounds that help bring inflammation to a close. Researchers think that when membranes carry much more arachidonic acid than EPA, the balance may tilt toward inflammation that switches on easily and resolves slowly. That kind of chronic low-grade inflammation is one of the processes most closely tied to aging of the heart, blood vessels and brain.

The fats in cell membranes also shape how cells signal, how flexible they are, and how well the mitochondria inside them work. So the ratio is a window into the raw material the body has for both inflammation and its resolution. The research below adds an important twist, though. Higher linoleic acid itself has not been linked with more heart disease in large studies, and in pooled data it was linked with less, while higher EPA and DHA are consistently linked with better outcomes. That suggests the most useful part of a high ratio is usually what it says about omega-3 intake.

From a root-cause view, the ratio reflects food choices over months, including how often someone eats fish and seafood, how much ultra-processed and fried food is in the diet, and which oils are used at home. Blood sugar balance, body weight, smoking and genetics affect how fats are converted and used. Because the ratio links so closely to inflammation, I find it most helpful to read it alongside hs-CRP and the Omega-3 Index rather than on its own.

What does the research show about omega-6, arachidonic acid and the ratio?

A Japanese community study looked at the AA-to-EPA balance directly. In 2013 in Atherosclerosis, Ninomiya and colleagues followed 3,103 community-dwelling adults aged 40 and older in the Hisayama Study for an average of 5.1 years, during which 127 had a cardiovascular event. Among people with hs-CRP of 1.0 mg/L or higher, each 0.20 drop in the serum EPA-to-AA ratio was linked with a 1.52 times higher risk of cardiovascular disease, mainly coronary heart disease rather than stroke, while no clear link appeared in people with lower hs-CRP. The DHA-to-AA ratio showed no such link. Japanese adults eat much more fish than most Americans, so the findings may not carry over directly, and fatty acids were measured only once.

A large study of older women looked at each fat separately. In 2017 in the Journal of Clinical Lipidology, Harris and colleagues measured red blood cell fatty acids in 6,501 women aged 65 to 80 in the Women’s Health Initiative Memory Study and followed them for a median of 14.9 years, during which 1,851 died. Each one standard deviation higher Omega-3 Index was linked with an 8 percent lower risk of death, with a hazard ratio of 0.92, and EPA showed a hazard ratio of 0.89. Linoleic acid and arachidonic acid were not linked with death in either direction. The study included only older women and, as an observational study, cannot show cause and effect.

The largest look at omega-6 fats pooled data from around the world. In 2019 in Circulation, Marklund and colleagues combined individual data from 30 prospective studies in 13 countries, covering 68,659 people and 15,198 cardiovascular events. Comparing the high and low ends of linoleic acid, the hazard ratios were 0.93 for total cardiovascular disease and 0.78 for cardiovascular death, meaning higher linoleic acid was linked with lower risk. Arachidonic acid was not linked with higher risk, and the highest levels were linked with slightly lower total cardiovascular disease. These were observational studies with different methods, and some of the authors reported food industry funding, so the results support a reassuring view of omega-6 rather than proof that more omega-6 is protective.

Related reading

If you would like to explore related topics, my articles on the Omega-3 Index, IL-6 and small dense LDL go deeper. You can also see the specialty tests I commonly recommend on my functional labs page.

Common questions about Omega-6 to Omega-3 Ratio

What is the difference between the omega-6 to omega-3 ratio and the AA-to-EPA ratio?

The omega-6 to omega-3 ratio compares all omega-6 fats with all omega-3 fats, while the AA-to-EPA ratio compares arachidonic acid with EPA specifically. Both are reported on many fatty acid panels.

Does a high ratio mean I eat too much omega-6?

Not usually. A high ratio most often reflects low omega-3 intake, and large studies have not linked higher linoleic acid, the main omega-6 fat, with more heart disease.

How is this ratio related to the Omega-3 Index?

The Omega-3 Index measures EPA and DHA as a share of red blood cell fats, and it usually moves in the opposite direction from the ratio. When omega-3 levels rise, the ratio tends to fall.

Sources

This article is for educational purposes only and is not medical advice. It does not replace an individual evaluation. Talk with your healthcare provider before making changes to your diet, exercise, supplements, or medications, especially if you are pregnant, nursing, or managing a health condition.