Wherever you look, the advice is the same: if you want to reduce your risk of heart disease, obesity, cancer and all manner of other health problems, you should cut down on “bad” saturated fats, such as those found in butter and red and processed meats. Instead, you should be gobbling “good” polyunsaturated fats. That means cooking with vegetable oils and mainlining leafy greens, oily fish, nuts and seeds. Simple.
Except when it comes to nutrition science, nothing is ever simple. In this case, the complications arise from the growing realisation that “good” fats aren’t all created equal — more specifically, that while omega-3 fatty acids are indeed good for us, omega-6s might actually be damaging your health.
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The idea that the balance of omegas in the food we eat can have an impact on our health is well established. It is also clear that the typical Western diet has become skewed in favour of more omega-6s and fewer omega-3s over the past 50 years, while at the same time we have seen a surge in the incidence of diseases associated with excessive inflammation, including heart disease and type 2 diabetes.
All of which has led to claims that we should not only seek to boost the amount of omega-3s in our diets, but also to cut down on omega-6s. Yet correlation isn’t causation. So can it really be that consuming too many omega-6s, long thought beneficial, is bad for us? And if so, what foods should we all be eating more or less of to optimise our omega balance?
Let’s start with a few basics. All the fats and oils we eat are composed of fatty acids, which fall into different categories according to their chemical composition. Each affects your physiology in different ways, with knock-on effects for your health. “The quality and type of fat that people eat has a huge impact on age-related diseases, particularly cardiovascular disease,” says , a nutritional immunologist at the University of Southampton, UK.
What are omega fatty acids?
Omega-3 and omega-6 fatty acids are called polyunsaturated fatty acids because they have many double bonds in the long chains of carbon that make up their backbones, whereas saturated fatty acids have none. They are considered “essential” fatty acids, as your body can’t make them, meaning you have to get them from the foods you eat. If you didn’t, you would get seriously ill — the omega family is known to play a vital role in immunity, brain and heart health and pregnancy (see “Omega-3s in pregnancy“, below).
The good news is that it isn’t difficult to get enough of them in your diet, as long as you eat the right foods. There are three main types of omega-3s: alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). ALA is found mainly in plants, so good sources include leafy green vegetables, flaxseeds and rapeseed oil. But while our bodies can synthesise DHA and EPA from ALA, they don’t do it very efficiently. That is why oily fish such as mackerel, salmon and sardines — all of which contain high levels of DHA and EPA — are considered the most important source of omega-3s.
The main source of omega-6 in our diet is linoleic acid (LA). This is found in seeds, nuts, grains, common vegetable oils such as sunflower oil and cornflower oil, and products made from them, including margarines.
Things get more complicated when we look at what omega fatty acids actually do in our bodies. One of their primary roles is in the cell membrane, where they are integrated into a double layer of fat molecules known as phospholipids. These contain a mix of fatty acids and proteins that control what enters and exits the cell, thus influencing how it behaves.
Importantly, the composition of fatty acids in the cell membrane changes in response to what we eat, with consequences for cell function, says Anthony Hulbert, author of the 2023 book If you have a diet too rich in omega-6 or too deficient in omega-3, he explains, your cell membranes will contain a lot more of the former than the latter. To make matters worse, the enzyme responsible for converting ALA into DHA and EPA can’t tell the difference between ALA and LA. This means if your body is awash with omega-6, the two fatty acids compete, resulting in less DHA and EPA.
When that happens, says Hulbert, the result is chronic inflammation, the driving force behind many of the health conditions that are growing ever more common in Western societies today. These include heart diseases, Crohn’s disease, type 2 diabetes, rheumatoid arthritis, Alzheimer’s, Parkinson’s and some cancers. “Omega-6s are important and healthy essential fats,” says Hulbert, an emeritus professor at the University of Wollongong, Australia. “But if they are eaten in excessive amounts, omega-6s will diminish the omega-3 content of cell membranes, driving chronic inflammation.”
There is a plausible physiological mechanism to connect omega-6s and inflammation. It relates to molecules called eicosanoids, which the immune system uses to convey messages, thereby helping us fight off invaders or heal tissues. Some eicosanoids are made from omega-3s and these tend to be anti-inflammatory. Those made from an omega-6 fatty acid called arachidonic acid (ARA), which is itself synthesised from linoleic acids, are pro-inflammatory.
The idea, then, is that consuming excessive amounts of omega-6 causes cells in the immune system to churn out more pro-inflammatory molecules, causing chronic inflammation.
There is also some evidence for this. For example, studies in humans and other animals show that replacing omega-6s with omega-3s has a positive effect on health, alleviating symptoms associated with chronic conditions like diabetes, heart disease and obesity.
What’s more, it is certainly true that the ratio of omega fatty acids we consume in our diets has changed dramatically over the past half-century, with the proportion of omega-6s having risen a great deal.
Hulbert puts these ratios as percentages, where a higher percentage denotes more omega-3 in relation to omega-6. Up until 1910, he says, a typical US diet had an omega balance of around 40 per cent. By 2010, it had dropped to about 9 per cent. The change can be attributed to three things: food manufacturers switching from primarily using animal fats to vegetable oil; farmers feeding their cattle grains rather than grass; and the rise of ultra-processed foods heavy in omega-6s. Over the same period, inflammatory conditions have become increasingly prevalent.
The coincidence is suggestive. However, when it comes to establishing a causal connection between omega-6s and inflammatory conditions, the results from human studies are mixed.
In a 2018 , Calder and Jacqueline Innes, then also at the University of Southampton, UK, concluded that “studies in healthy human adults have found that increased intake of ARA or LA does not increase the concentrations of many inflammatory markers” and that “epidemiological studies have even suggested that ARA and LA may be linked to reduced inflammation”.
Calder says that one reason why the results are inconclusive is that our cells already contain such high amounts of ARA that further supplementation is likely to have no effect. “The conundrum is that omega-6s are considered to be harmful, and you can map that out really easily in theory, but when you look at the human data, it doesn’t quite pan out like that,” he says. “If you give people more LA through supplements, you do not increase ARA in their membranes, but maybe this is because they are already saturated.”
The evidence for the beneficial role of omega-3s is much stronger. “What’s clear is that if you increase your intake of EPA and DHA and decrease the amount of ARA in your cell membranes, it will reduce inflammation,” says Calder.
Omega-3s also seem to be particularly important for brain function. In 2020, for example, at the University of Bordeaux in France and her colleagues published a study in which they followed 10,000 older adults in France over 17 years. They found that and slower brain atrophy — and were less likely to develop dementia. Some scientists believe that omega balance is also linked to depression and other mental health conditions.
Omega-6s and inflammation
There is little doubt that, for most people, getting more omega-3s would be beneficial. But whether we need to increase our intake of omega-3s and cut down on omega-6s, as Hulbert recommends, is up for debate. “There is little evidence for a role of omega-6 on cognitive decline, either positive or negative,” says Samieri. “Some argue that the omega-3/omega-6 ratio is important. However, in practice, in epidemiological research, it is really the level of omega-3 which is important.”
Similarly, at King’s College London says that as long as you have an adequate amount of omega-3 in your diet, there isn’t much convincing evidence that omega-6 is bad for you. “The omega balance theory is based on the effect that omega fatty acids have on eicosanoids,” she says. “However, the research that has been done in cells and animals to support this theory, in my opinion, does not play out in humans. I would consider omega-6 to be a healthy nutrient, especially for heart health”. For instance, it is one of the best fats at lowering your amount of LDL cholesterol, she says — high levels of which are known to raise your risk of heart disease and stroke.
It could also be that something else is driving the increase in inflammatory conditions. A great deal of omega-6, particularly in the US, is consumed in the form of ultra-processed foods. “There are so many other mechanisms by which these foods may impact our health rather than the omega-6,” says Berry.
For his part, Calder agrees with Hulbert that most people eating a Western diet would benefit from increasing consumption of omega-3s whilst simultaneously eating less omega-6s. “Exchanging one [omega-3] for the other [omega-6] is better than changing just one of them, because you’re changing both sides of the equation,” says Calder.
The question then becomes what to eat to optimise your ratios. Answering that might seem fraught with difficulty, not least because food labels typically only offer the total polyunsaturated fat content, rather than the relative amounts of omega-3 or omega-6.
But there are a few ways to make a difference. To raise your omega-3 levels, the most important thing is to eat more oily fish. “This is the best way to get more preformed EPA and DHA,” says Calder. If that isn’t possible, there are plant-based alternatives that contain high levels of ALA, which your body will then have to convert to EPA and DHA. Hulbert recommends green leaves, as what little fat they do contain is all ALA. Meanwhile, Calder recommends walnuts, along with flax and chia seeds. “I would also try to reduce omega-6 intake by replacing corn oil, or sunflower oil, with rapeseed oil,” he says.
You do have to be careful, though, because even if you eat foods that are naturally high in omega-3, if they are cooked or stored in omega-6-rich oils, the omega balance will still be low. Hulbert explains that tuna canned in water has an omega balance of 90 per cent, meaning it contains lots of omega-3s and not many omega-6s. When it is canned in sunflower oil, this drops to 16 per cent. Wild-caught fish have a better omega balance, ranging from 63 to 83 per cent, compared with farmed fish of the same species, ranging from 13 to 67 per cent.
If you do eat meat, Hulbert recommends grass-fed beef and lamb, which are good sources of omega-3s. He tends to avoid pork and chicken because they are commonly fed on grain containing soya and corn, which means they are high in omega-6s. He adds that you should also avoid ultra-processed foods, since they are often made with vegetable oils.
As for fish oil supplements, it is vital to check the label to see how much EPA and DHA they actually contain. “If you have a bog-standard fish oil supplement, the amount of EPA or DHA in it is probably around 300 milligrams, whereas if you go home and eat salmon tonight for dinner, it will have around 1.5 grams — over five times as much,” says Calder. However, even low doses of omega-3 over long periods may be beneficial, or at least better than doing nothing at all.
“In the UK, we probably eat about five times more omega-6s than omega-3s, and in the US it is more extreme — probably at least 10 times or more,” says Calder. “If you can redress that balance and up the levels of EPA and DHA in your cell membranes, that is compatible with better health and well-being.”
Omega-3s in pregnancy
Maybe the most compelling evidence that the balance of omega fatty acids in our diets has a big impact on our health (see main story) comes from studies of pregnant women.
In 2020, at the University of Adelaide in Australia and his colleagues reported a randomised controlled trial in which 5000 women pregnant with a single fetus received either a pill containing 900 milligrams of omega-3 fish oil or a control vegetable oil capsule. were clear: if the participants had low levels of omega-3s, they were more at risk of having a preterm birth.
"Not only that, but if those women were given a supplement of omega-3, their risk of preterm births dropped by about 77 per cent," says Gibson.
The reasons why having low omega-3 levels may increase the risk of premature birth aren't known. But Gibson says the women who had a higher risk of preterm birth weren't just deficient in omega-3, they were also high in omega-6. "So there is clearly a balance, and when we correct that and get the balance right, we can overcome the tendency of a mother to give birth prematurely."
This data was used to inform new guidelines issued by the Australian government in 2021. The guidelines state that people who are pregnant should supplement their diet with 800mg of docosahexaenoic acid and 100mg of eicosapentaenoic acid, two types of omega-3 fatty acid, per day, due to their potential to reduce preterm birth.
Jasmin Fox-Skelly is a science journalist based in Cardiff, UK
