French fries cooked in seed oil. Credit: Peggy_Marco, Pixabay
Seed oils like sunflower oil, canola oil, and soybean oil are found in lots of everyday foods, from salad dressings and sauces to crisps and nuts, plus ready meals and bakery items.
While many scientists say they offer health benefits when used in moderation, a growing number of critics argue they may fuel inflammation, disease and even sunburn. With conflicting opinions across studies, social media, and nutritional circles, what do we really know about seed oils?
Why are seed oils so widely debated?
Seed oils are vegetable oils made from the seeds of plants, including corn, soybean, sunflower and canola. They’re often used in cooking and are common in ultra-processed foods (UPFs). But their reputation has come under fire in recent years.
Paul Saladino, MD, a well-known critic of seed oils, argues that processed foods, processed sugars and seed oils have no place in the human diet. “By far the biggest villain in my opinion are seed oils, or oils derived from plant seeds AKA canola, sunflower, corn, soy, cottonseed, etc.
Also known as polyunsaturated fats or linoleic acid, these are not a species-appropriate source of fat for humans, yet we are consuming a ton of them. Yes, via processed foods and seed oils, but also from “healthy” nuts and seeds, and even chicken and pork (which store it in their fat and then pass it on to us).
Excess linoleic acid accumulates in the body and appears to “break” fat cells, causing them to release fat as they balloon and expand. These free fats induce insulin resistance in the peripheral muscles, causing inflammation and DNA damage.
Our ancestors consumed very little linoleic acid, and modern-day hunter gatherers (like the Hadza and Maasai) only consume 2-3% as part of their total calories. Meanwhile, many people are consuming up to 20% of their calories from this bullsh*t.
I believe excess linoleic acid is the biggest driver of chronic disease, and my deep hope is that the world wakes up to this fact soon.”
US presidential candidate RFK Jr has also voiced concern, claiming seed oils are “associated with all kinds of very serious illnesses including body-wide inflammation,” and are “one of the most unhealthy ingredients that we have in foods” (Cited by The Diary of a CEO.)
Many concerns focus on omega-6 fatty acids, particularly linoleic acid, found in high amounts in seed oils. But do these claims match the evidence?
What scientists say about seed oils and inflammation
Much of the criticism stems from the idea that omega-6s contribute to chronic inflammation.
“New research shows that omega-6 fatty acids give rise to unique natural molecules, like lipoxins, that have powerful anti-inflammatory effects in the body,” says Prof Dariush Mozaffarian of Tufts University (BBC).
Christopher Gardner, a nutrition researcher at Stanford University, also rejects the idea that seed oils are inflammatory. “This argument is not supported by tightly controlled clinical trials,” he told the BBC. “If anything, it’s shown to be anti-inflammatory… levels of inflammatory molecules actually reduce.”
A large 2019 meta-analysis found that people with higher levels of linoleic acid in their blood had a 7 per cent lower risk of developing heart disease. According to researcher Matti Marklund: “Linoleic [acid] might improve cholesterol… and also improve glucose metabolism, which reduces the risk of type 2 diabetes”
Do seed oils make you more susceptible to sunburn?
Some online sources claim that seed oils make people more vulnerable to sunburn and skin damage.
One article states: “UV rays cannot initiate lipid peroxidation without a catalyst, which is seed oil… You can think of UV rays as the match, and seed oils as the gasoline” (Ifixhearts.com).
The theory is based on oxidation of polyunsaturated fats in the skin when exposed to sunlight. However, there is no peer-reviewed human research confirming this link.
Harvard dietitian Alison Kane recommends not overreacting: “Using a few tablespoons to sauté vegetables or in a salad dressing is a healthy option,” she told Harvard Health.
Seed oils and cancer?
Some studies have explored a possible link between omega-6 intake and cancer, particularly triple negative breast cancer (TNBC).
A 2024 study published in Nature found that linoleic acid might promote tumour growth in TNBC, an aggressive subtype. “TNBC seems to respond the most to omega-6 linoleic acid,” said lead researcher Nikolaos Koundouros (BBC).
Seed oils vs animal fats
Some campaigners have called for a return to traditional fats like beef tallow or butter. RFK Jr is selling T-shirts that say: “Make Frying Oil Tallow Again.”
However, a 42-study meta-analysis found that seed oils reduced cholesterol and inflammation more effectively than saturated fats.
Alternative health voices like Carnivore Aurelius argue that seed oils are not just suboptimal, but directly harmful. In a widely circulated blog post, he writes: “Eating seed oils is like playing Russian roulette with a fully loaded gun”.
His key points include:
- Mitochondrial damage from linoleic acid disrupting cardiolipin membranes in cells, leading to energy loss and inflammation.
- Toxic breakdown products like 4-HNE and MDA forming during oxidation, linked to cancer, Alzheimer’s, and obesity.
- Accumulation in body fat, with linoleic acid now making up over 20 per cent of fat stores in modern humans, compared to 2–3 per cent in traditional societies.
- A claim that “PUFAs are the primary dietary driver of modern chronic diseases” and that we should instead “bring back saturated animal fats like tallow and butter.”
He also references the Sydney Heart Study, which found worse heart outcomes in men who consumed more seed oil. However, researchers have pointed out the oils in that study were partially hydrogenated and contained trans fats, which are now limited or banned in many countries.
Are ultra-processed foods the real problem?
Experts say the issue might not be the oils themselves – but the foods they appear in.
Jason Ewoldt of the Mayo Clinic explains: “The seed oil is not the likely driver for negative health effects… Processed foods also tend to have higher levels of refined carbohydrates, salt and sugar”
Prof Mozaffarian agrees: “The dangers arise from too much starch, sugar, and salt, loss of natural intact food structure, and dozens… of artificial additives.”
What’s the verdict on seed oils?
The debate over seed oils is unlikely to end soon. While early lab research has raised valid questions – particularly about specific cancers and oxidation – most large-scale, peer-reviewed studies suggest that seed oils, in moderation, are not harmful, and may in fact offer several heart health benefits.
But as critics point out, more long-term, high-quality human trials are needed, especially in light of rising chronic disease rates and growing seed oil consumption.
Should we rethink our relationship with seed oils, or are they being unfairly blamed for broader dietary problems? The evidence is still evolving.
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