If social media is to be believed, seed oils are one of the biggest problems in modern diets. Rapeseed oil supposedly causes inflammation, sunflower oil ruins your health, and the most sensible thing to do would apparently be to return to butter and animal fats.
There is, however, one small problem with this theory. Scientific research does not tend to support it very well.
This does not mean that every vegetable oil is automatically healthy or that heating oils cannot produce harmful compounds. It does mean, however, that a single fatty acid, a few laboratory experiments and a scary video are not enough to condemn an entire food group.
Let's look at what seed oils actually contain, where the inflammation claim originated and what decades of scientific evidence tell us about their effects on health.
What does “seed oil” actually mean?
The term “seed oils” is not commonly used in nutritional science. In online debates, it usually refers to eight oils: rapeseed, corn, cottonseed, grapeseed, rice bran, safflower, soybean and sunflower oil. Most of these are extracted from seeds, but rice bran oil is made from the outer layers of the rice grain. Olive and avocado oil are mainly extracted from the flesh of the fruit. Products sold in shops as “vegetable oil” are often a blend of these oils (Rosen, 2025).
However, seed oils are by no means all the same. For example, rapeseed oil is predominantly made up of monounsaturated fats, which are also abundant in olive oil. Rapeseed oil also contains essential omega-3 and omega-6 fatty acids and relatively little saturated fat. Regular sunflower oil, by contrast, contains more polyunsaturated fats (Canadian Grain Commission, 2018; Sacks et al., 2017).
So not all seed oils can be lumped together. Their composition varies, and the label “seed oil” alone tells us very little about how an oil affects health.
Where does the inflammation claim come from?
On paper, it all seems quite logical. Many seed oils are rich in linoleic acid, an omega-6 fatty acid. The body can convert linoleic acid into arachidonic acid, which in turn can give rise to compounds involved in the inflammatory response. So more linoleic acid should mean more inflammation.
Except that human metabolism is not so simple that adding a single substance lets us automatically predict the outcome. To test this, we need to look at what actually happens inside the human body.
A review published in 2012 examined 15 randomized trials in which linoleic acid was added to the diets of healthy people and inflammatory markers such as CRP, IL-6 and TNF-α were measured. Linoleic acid did not increase these markers. The authors concluded that randomized trials provide no evidence that linoleic acid raises inflammatory markers, but all the studies were small (Johnson & Fritsche, 2012).
In a large pooled analysis, blood levels of arachidonic acid were not associated with a higher risk of cardiovascular disease either (Marklund et al., 2019).
What does heart health research say?
If seed oils were really as harmful to the heart as social media claims, we would expect this to show up in long-term studies too. So far, the findings have tended to suggest the opposite.
For example, in one large pooled analysis, researchers examined data from nearly 69 000 people and found that higher levels of linoleic acid in the body were associated with a lower risk of death from cardiovascular disease. This does not yet prove that linoleic acid itself protects the heart, but it does call into question the claim that this fatty acid is inherently harmful (Marklund et al., 2019).
An even more important question is what we replace a particular fat with. For example, using vegetable oils that contain more unsaturated fat instead of butter may reduce the risk of heart disease. A review by the American Heart Association estimated this reduction at approximately 30%. A comprehensive Cochrane review of studies likewise found that reducing saturated fat intake over the long term lowered the risk of cardiovascular events by about a fifth. However, a reduction in all-cause mortality was not clearly demonstrated (Sacks et al., 2017; Hooper et al., 2020).
This is precisely why the Nordic Nutrition Recommendations (NNR 2023) also recommend choosing vegetable oils containing unsaturated fats over butter and other fat sources rich in saturated fats (Nordic Council of Ministers, 2023).
This does not mean that butter is now forbidden or that every drop of vegetable oil automatically improves your health.
If your daily diet consists largely of fast food and ultra-processed products, and your saturated fat intake is already high, it is worth considering whether butter is really the most sensible fat to use in cooking as well.
However, if your diet is generally varied and balanced and your saturated fat intake stays within recommended limits, there is no reason to worry about occasionally frying with butter. Ultimately, our health is not determined by any single food, but by what and how much we eat over time.
Do all studies say the same thing?
If all studies showed exactly the same result, this article would be much shorter. In science, though, things are rarely that simple.
Critics of seed oils often point to two studies conducted decades ago. In these studies, some of the fats people normally consumed were replaced with vegetable oils to investigate whether this might benefit heart health.
The results of the Sydney Diet Heart Study were surprising. Although cholesterol levels fell among participants who consumed vegetable oil, mortality was actually higher among them (Ramsden et al., 2013).
A similar question arose when analysing the results of the Minnesota Coronary Experiment. Participants’ cholesterol levels fell there too, but no clear benefit in terms of mortality was found (Ramsden et al., 2016).
Does this mean seed oils are unhealthy after all, even though cholesterol levels fell? Not necessarily. Both studies had limitations, and data recovered decades later do not give the full picture. They do, however, remind us of one important point: a drop in cholesterol levels does not automatically mean a person will live longer.
Based on these findings, some researchers have suggested that compounds formed during the oxidation of linoleic acid may increase the risk of heart disease (DiNicolantonio & O’Keefe, 2018). However, this is a hypothesis, not a proven causal link.
Looking at the evidence as a whole, larger research reviews support the view that partially replacing saturated fats with unsaturated fats benefits heart health (Sacks et al., 2017). So, while conflicting findings deserve attention, they do not prove that seed oils are harmful to health.
Is frying with rapeseed oil a problem?
The critics’ second strong argument concerns heating. When polyunsaturated fatty acids are heated, they break down and form aldehydes, compounds that can be toxic.
Martin Grootveld’s research team at De Montfort University has measured these in the laboratory. In one experiment, oils were heated at 180 °C for up to 90 minutes. The most aldehydes formed in sunflower oil, which is rich in polyunsaturated fatty acids, and fewer formed in rapeseed and olive oils, which are rich in monounsaturated fatty acids (Grootveld et al., 2021). Another study found toxicologically significant amounts of aldehydes in potato chips fried in sunflower oil, with the amount increasing after repeated frying (Moumtaz et al., 2019).
These measurements were taken under laboratory conditions: they show aldehyde formation in oil and food, not illness in humans. The practical takeaway is that the composition of oil changes when heated, and breakdown products can accumulate with repeated use. Under the conditions studied, more aldehydes formed in sunflower oil than in rapeseed oil (Grootveld et al., 2021).
Using rapeseed oil to fry eggs at home is one thing; heating the same oil for hours at a high temperature and reusing it repeatedly is quite another. Although both involve frying, the duration and temperature of heating significantly affect how much the oil breaks down.
Why do seed oils still have a bad reputation?
One reason is a correlation that appears causal. According to Christopher Gardner, director of nutrition studies at the Stanford Prevention Research Center, the argument “seed oil consumption has doubled, and obesity has risen at the same time” sounds convincing, but this is correlation, not causation (Rosen, 2025). Two things can happen at the same time without one causing the other.
I should point out here, though, that the amount consumed also matters. As with all types of fat, excessive consumption of seed oils can contribute to weight gain if energy intake exceeds energy expenditure.
Another reason lies in the foods in which seed oils are used. They are often found in potato chips, ready meals and sauces, for example. Frequent consumption of such products may be associated with poorer health, but seed oil itself cannot automatically be blamed. The overall composition of the food, its energy density and eating habits also matter (Rosen, 2025).
A third scary-sounding word associated with seed oils is hexane. This solvent is used in the production of some vegetable oils to extract oil from seeds. Most of the hexane is removed during processing, and limits have been set for any residues. So the use of hexane in production does not automatically mean that the finished oil is harmful to health.
Who is funding this research?
In 2026, a comprehensive scientific review was published whose authors concluded that existing research does not support widespread fears about the health effects of seed oils (Nagra et al., 2026).
But there is an interesting detail here. The review was partly funded by organisations linked to the soy industry, which naturally have an interest in maintaining a positive reputation for soybean oil. Does this mean the findings are wrong? Not at all. However, it is important to be aware of such funding, because potential conflicts of interest can influence which questions are investigated and how the findings are interpreted.
That is why you should not form your opinion based on a single review, however convincing its conclusions may be. In this case, the overall conclusion is also supported by other extensive research, including reviews by Cochrane and the American Heart Association (Hooper et al., 2020; Sacks et al., 2017).
Frequently asked questions
Is olive oil better than rapeseed oil?
Nordic and Baltic dietary recommendations consider both olive oil and rapeseed oil to be good sources of fat (Rosqvist & Niinistö, 2024). But if I had to single out one of the two, it would be extra virgin olive oil. In addition to its beneficial fatty acid profile, it contains antioxidant compounds, and its health effects have been extensively studied. Rapeseed oil is also a perfectly reasonable choice, but olive oil stands out for the particularly strong scientific evidence supporting its benefits as part of a varied and balanced diet.
Do you need to cut out butter and lard?
You do not need to eliminate saturated fats from your diet completely. What matters is keeping track of how much you consume each day. According to the Nordic and Baltic dietary recommendations (NNR), saturated fats should provide less than 10% of daily energy intake. What you replace saturated fats with also matters. Research suggests that replacing them with unsaturated fats, rather than refined carbohydrates or added sugar, is more beneficial for heart health (Sacks et al., 2017).
Are seed oils to blame for fast food being unhealthy?
Seed oils are often found in crisps, fast food, baked goods and other ultra-processed products. Since eating these foods frequently can negatively affect health, it is easy to conclude that the oil they contain must be to blame. In reality, it is not that simple. Their high energy density, salt and sugar content, and how often and in what quantities they are eaten also play a role. Seed oil is just one ingredient among many, and there is no reason to consider it the main culprit behind fast food being unhealthy.
Which oil should you use for what?
For salads and cold dishes: extra virgin olive oil or cold-pressed rapeseed oil. These are rich in unsaturated fatty acids and are well suited to use without heating.
For everyday frying: olive oil or refined rapeseed oil. These predominantly contain monounsaturated fatty acids, which are relatively stable when heated. Regular butter is also suitable for frying over low to moderate heat.
For frying at higher temperatures: refined rapeseed oil or high-oleic sunflower oil. These are generally more stable when heated than regular sunflower oil, which is rich in linoleic acid.
Avoid letting oil smoke and reheating it repeatedly. High temperatures and prolonged heating promote the breakdown of oil and the formation of undesirable compounds.
Summary
Based on the research to date, there is no reason to fear seed oils. However, this does not mean that all oils are equally good choices. For example, there is strong scientific evidence in favour of extra virgin olive oil, but rapeseed oil can certainly be part of a healthy diet too.
When it comes to seed oils, it is worth remembering that no oil is a miracle cure in itself, nor is it automatically the enemy. It is important to look at the bigger picture: which oil is used, how it is heated and what the rest of the diet looks like.
Alarming claims circulating on social media may sound convincing, but individual studies or laboratory experiments are not enough reason to throw all seed oils out of your kitchen.
This article is not a substitute for personalised nutritional or medical advice.
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