Unlike animal-based products, seed oils contain predominantly unsaturated fats. Photo / 123rf
The No Seed Oil Movement has America and health influencers in its grip, but experts say the cooking staple is being mistakenly demonised.
In early 2022, an American doctor called Cate Shanahan coined the term, “The Hateful Eight” to describe a group of seed oils commonly used in foods – canola or rapeseed, corn, cottonseed, soybean, sunflower, safflower, grapeseed, and rice bran oils.
On social media and in a book called Dark Calories, Shanahan, who brands herself as “Mother of the No Seed Oil Movement”, describes seed oils to her many thousands of followers as being uniquely harmful, inflammatory, and creating damage to our cells through oxidative stress.
In the US, such rhetoric, spread through numerous doctors and lifestyle influencers, has now reached the highest level of Government. As part of his “Make America Healthy Again” agenda, Robert F. Kennedy jnr, the US Health Secretary, has claimed that Americans are being “unknowingly poisoned” by seed oils, calling for restaurants to return to using animal fats instead. In response, major chains ranging from Sweetgreen to Steak ‘n Shake have followed suit, in many cases swapping seed oils for beef tallow.
Yet despite the social media storm surrounding them, nutrition researchers who study seed oils, say that this contradicts decades’ worth of evidence. For example, in one major study which followed more than 220,000 people for three decades, participants with the highest intake of plant-based oils, including both olive and seed oils, had a lower risk of premature death, compared with those who consumed more animal-based fats.
Richard Bazinet, a professor in the University of Toronto’s department of nutritional sciences, blames the rise of seed oil misinformation on the increasing need to manufacture drama in order to build a social media profile.
“If you’re an influencer, it’s hard to just say, ‘Hey, eat a diet with less processed foods, get some exercise, don’t eat too much,’” says Bazinet. “It’s not a big selling point. So if you want to sell your book, you’ve got to come out and say, ‘You’ve been lied to!’”
Until the 1970s, people consumed a much higher proportion of animal fats, through products like lard or butter. However, concerns began to rise as research increasingly showed that consuming excess saturated fats, the predominant source of dietary fat in animal-based products, raises LDL cholesterol, which in turn increases heart disease risk over time.
As Philip Calder, a professor in nutritional immunology at the University of Southampton explains, these concerns led to a progressive shift away from animal fats towards seed oils in both food products and home cooking between the 1970s and the 1990s.
“There was a wholesale change in what was available in supermarkets and what people were using,” he says. “If you were born in that period, you probably grew up with vegetable oil-based margarine rather than butter, and if you’re cooking, you’re using olive, rapeseed, sunflower or corn oil.”
These plant-based oils contain predominantly unsaturated fats – mono and polyunsaturated fats – which are liquid rather than solid at room temperature. Researchers believe that one of the key reasons why they are being mistakenly demonised is because seed oils are readily used in many ultra-processed foods (UPFs) because they are a cheap and easy way of improving shelf-life and adding crisp and creamy textures.
However, Bazinet and others argue that the major issue with UPFs is not so much the seed oils, but simply the poor overall nutritional value of these products, because of the excess of added sugars, salt and refined carbohydrates. “I’m not convinced that if you take your potato crisps and cook them in something else, then all of a sudden they’re going to be great for you,” he says. “If you replace seed oils in these foods, I still think it’s going to be junk food.”
One of the main arguments used against seed oils is that they are rich in omega-6 fatty acids. While these are essential nutrients, just like omega-3s, which we need to extract from our diet, seed oil detractors typically highlight the skewed omega-6 to omega-3 ratio which can be as high as 50:1. Given the prevalence of seed oils in today’s diet, omega-6s can account for 15% of our total energy intake, and their detractors claim that this imbalance is driving chronic inflammation in the body.
However, according to Penny Kris-Etherton, distinguished professor of nutrition at Penn State University, such misinformation stems from a key misunderstanding of how linoleic acid, one of the major omega-6 fats present in seed oils, is metabolised in the body. She explains that we have various enzymes which convert linoleic acid into another omega-6 fat called arachidonic acid, which in theory, is then broken down into various inflammatory chemicals.
In reality, says Kris-Etherton, our body has a brake mechanism which prevents this from happening. Research has shown that just 0.2% of the linoleic acid we consume actually gets converted into arachidonic acid. “There are many studies on that,” she says. “Even when you feed someone very, very, very high levels of linoleic acid, you just do not see increased markers of inflammation.”
In fact, studies have typically shown that people with higher levels of linoleic acid in their blood are less likely to get heart disease, as this fat has been shown to actively lower LDL cholesterol.
Instead of fixating so much on omega-6s, Calder says that the bigger problem reflected by studies on the omega-6 to omega-3 ratio, is that most people are getting too few omega-3s.
Another argument made against seed oils is that they may contain trace amounts of harmful chemicals because of the refining processes used to produce them. While more expensive cold-pressed seed oils are produced by squeezing the seeds, cheaper versions are typically extracted with hexane, a solvent which comes from crude oil.
While factory workers who breathe in high amounts of hexane are known to be at risk of multiple health conditions, Kris-Etherton says that any hexane still found in supermarket seed oils is likely to be trace amounts as the products undergo a rigorous clean-up process to remove potentially harmful chemicals.
“There’s really no evidence that the small amount of hexane we might get from uncooked seed oils is bad,” she says. “I think it’s something we still need to look at a little more carefully, and maybe regulate the amount of hexane that can be present in these oils. But also, as soon as you cook the oil, even lightly, any hexane present will blow off.”
But what about oxidative stress? Calder says it is true that the polyunsaturated fats within seed oils are prone to undergoing a chemical reaction called oxidation when heated, much more so than saturated fats, a process which generates chemicals that are harmful to our cells. “Imagine a fast-food restaurant using vegetable oils for high temperature frying, and they’re repeatedly using the same oil,” he says. “That oil becomes destroyed over time, and full of oxidised products.”
However, he says that it’s not the oil itself which is the problem in these cases, but how it’s being used. He also points out that in the UK, there are regulations which prevent large fast-food chains from reusing vegetable oils for this very reason.
When it comes to the bottle of seed oil on your shelf, or frying these oils in your own home, Kris-Atherton says that oxidation is unlikely to be an issue for two reasons. First, she points out that seed oils are naturally rich in various antioxidants like vitamin E which are designed to protect them from oxidative damage caused by the sun’s UV rays. Second, she says that if you were consuming significant amounts of oxidised oils, you would soon know about it.
“When they become oxidised, the taste is terrible,” she says. “So that itself is self-limiting.
Shanahan lists olive, coconut and avocado oils, which all come from the fruits, as recommended alternatives to seed oils. But while olive oil’s beneficial qualities are well-known, researchers point out that there is also a rigorous evidence base for rapeseed oil, with studies showing that it actually drives greater reductions in LDL cholesterol compared with olive oil, and similar anti-inflammatory effects.
When pressed, Calder says he would rank rapeseed oil as having the best composition of beneficial fats out of all the seed oils, followed by soybean, then corn and sunflower.
But rather than focusing on one oil, Kris-Etherton recommends consuming a variety of different plant-based oils as they all contain varying compositions of useful fats and antioxidants. “Asking which seed oil is the best is a bit like asking are blueberries better than blackberries,” she says. “They all have different characteristics which confer health benefits.”
Calder’s biggest concern is that the spread of misinformation about seed oils will prompt growing numbers of people and food companies to start moving away from plant-based oils and back to animal fats. He fears that this could accelerate the growing numbers of people dying from heart disease, rates which have risen by 12% in the UK since 2020, having previously consistently declined for more than four decades.
“The risk is that people will suffer by moving away from a dietary change that was introduced to improve the population’s health,” he says. “But in 2025 we’re in an environment where there’s a proportion of the public who are very receptive to ideas being spread by influencers on social media with a big following. And we’re talking about seed oils today, but this is just one example of how we’re moving away from trust in science.”