Are seed oils toxic? It's complicated — here's what you need to know about the war over dietary fats

• Over the past few years, fears about toxic and inflammatory "seed oil" have taken over the internet.
• Many experts dismiss this, saying studies show cooking with vegetable oil is good for you.
• What seed oil is actually doing in our diet is more complicated than either side lets on.

In recent years, a war has been brewing over the fats we eat. Specifically, it's a fight over "seed oils." Are they as toxic as some health influencers believe?

Robert F. Kennedy Jr, President-elect Trump's pick for Health and Human Services secretary, is a leading figure in the fight. He has a line of t-shirts, bumper stickers, and red hats dedicated to "make frying oil tallow again," arguing for places like McDonalds to go back to using beef fat.

Nutrition experts say the discourse around so-called seed oils stokes unnecessary fear, obscuring the truth about what is already well-established about how to eat to promote human health and longevity.

Professor Richard Bazinet, who studies how fat fuels our brains at the University of Toronto, says online discourse about seed oils being the "root of all evil" has exploded since 2020.

"People are coming out and saying, 'Hey, the government's lying to you,'" he told Business Insider. "Saturated fats are good for you. Seed oils are actually what's killing you, causing cancer."

Let's not get it twisted: butter is not the salve here. But the health benefits of seed oils are also murky.

The seed oils under fire, aka 'the hateful 8'

For centuries, people around the world have used local oils, some of which could be classified as "seed oils," derived from mustard seeds and flaxseeds. None of those were bad for their health.

These days, "seed oil" is more of a pejorative term than a technical definition, referring to oils high in omega-6 fatty acid, including:

• Canola
• Corn
• Soybean
• Cottonseed
• Grapeseed
• Sunflower
• Safflower
• Rice bran

Some influencers call them "the hateful eight."

Do seed oils cause inflammation?

Opponents of seed oils say that they are toxic and often recommend butter instead, which is rich in saturated fatty acids with only small amounts of omega-6.

Cardiologist Dariush Mozaffarian, director of the Food is Medicine Institute at Tufts University, told BI he has found no compelling evidence that seed oils are harmful.

Mozaffarian has authored dozens of studies independently investigating how oils rich in omega-6 impact health issues like heart disease, stroke, and weight gain. He said he has found lots of evidence they're good for overall health, lowering type 2 diabetes rates, and improving cholesterol levels.

But he still can't convince some of his "very smart" friends to agree with him on this, including some nutrition scientists who say the concerning trends linked to omega-6 can't be waved away.

A long-term study of Eastern European countries in the 1990s found that those who used "seed oils" with a higher concentration of omega-3 had fewer heart disease deaths than countries that went with oil richer in omega-6.

One thing all researchers — including Mozaffarian — agree upon is that we need a healthy balance of the two essential fatty acids: omega-3 and omega-6. These days, we do not get enough omega-3.

There are clear trends showing that less omega-3 and more omega-6 in the diet is associated with more obesity, and operates on pathways in the brain that can encourage more eating, and tell the gut to store more fat. Studies link high omega-6 intake with more chronic pain, overeating, and potential mood issues while new research on omega-3 suggests supplementation can improve satiety and keep cognitive function going strong in old age.

Several scientists who've studied dietary fats at the National Institutes of Health told BI the internet's focus on specific oils obscures a deeper issue: omega-6 is infused in the American food system in myriad ways, distorting the nutrient density of what we eat.

From processed foods at the gas station, to seemingly innocent, seed oil-free items like chicken eggs, our nutrition equation has been thrown completely off balance.

Baked into the fabric of the modern American diet

A century ago, consumption of omega-6 fatty acids was less than 3% of our total calories.

That changed after World War II, when new technology made it possible to mass-produce new kinds of monounsaturated vegetable oils from plants rich in omega-6.

Canada invented canola, and many cooks swapped out dangerous trans fats for this cheaper, more accessible oil. Food producers also started making ultra-processed foods with things like canola oil or corn oil.

Suddenly, our modern eating era was born. There were some holdouts: McDonald's didn't stop using beef tallow until around 1990, but as vegetarianism and veganism became more popular, "seed" oils became the default inoffensive, dirt-cheap choice to manufacture, fry, and cook food for the masses.

Today, omega-6 accounts for roughly 10% to 20% of calories in the average American diet, which is dependent on a backbone of soy and corn.

It's unavoidable in our food system, and it's in prepared foods at higher concentrations than ever. It's in everything: corn chips, peanut butter, farmed salmon, even today's grilled chicken is higher in omega-6 than it used to be.

Getting enough omega-3 to balance this all out would be a tall order.

"We have a river of oils flowing through the food supply," psychiatrist and nutritional neuroscientist Joseph Hibbeln said.

Hibbeln is an expert in lipid biochemistry and brain health, and studied dietary fat at the National Institutes of Health for nearly three decades. He has seen through his research how these oils increase appetite, and change people's taste preferences so food companies can drive up sales. "It doesn't have to be a conspiracy, it's just: you sell more food."

Traditional Mediterranean diets, the favorite eating plan of most dieticians and nutrition buffs, had about a 1:1 ratio of omega-3's to omega-6's by default. There was plenty of olive oil, high in omega-9, but also a good amount of omega-3 fatty acids from foods like fatty fish, walnuts, and flaxseeds.

Still, Dr. Artemis Simopoulos, former chair of the nutrition coordinating committee at the National Institutes of Health, says demonizing "seed oils" misses the point. If most of your diet is ultra-processed, it doesn't matter what your McDonald's french fries are cooked in.

"This was a problem that was created by agriculture and food industry," Simopoulos told Business Insider.

This is not dissimilar from Mozaffarian's common refrain whenever anyone asks him if they should switch to avocado oil or beef tallow to prevent inflammation.

"There are things that are way more important for you than to even think about seed oils," Mozaffarian said. "I want people to be avoiding super processed foods and to be avoiding refined flours and sugars."

What does this mean for the food industry?

New alternatives to deep fryer "seed oils" are popping up, and gaining traction.

Take Zero Acre, an oil company developing monounsaturated oils made from fermented sugar cane. The company has investment from Chipotle, is used in the restaurants of Michelin-starred chefs, and had a collaboration with Shake Shack.

The oil industry is already bracing for a change in public sentiment, and not just with independent alternatives like Zero Acre.

Simopoulos has consulted for giant food companies like Nestlé and is working with farmers in China to plant more traditional camellia trees for cooking oil, since it's rich in omega-3. She and Bazinet, the University of Toronto researcher, both said big food giants are pivoting away from using omega-6-heavy oils, favoring omega-9, which is nonessential and doesn't compete with omega-3.

"Things are totally changing, and the sooner the better," she said.

Don't let fears about 'seed oil' derail a healthy diet

US health authorities speak in broad terms about nutrition, without diving too deep into the chemical and molecular differences between different fat sources.

They don't make any scientific distinction between seed oils and other unsaturated fat sources, and they don't talk much about the importance of balancing essential fatty acids. Their unwavering focus is on prioritizing "healthy fats" in the American diet, like omega-3 from salmon, and cutting out butter, which is linked to heart disease.

That general messaging doesn't sit well with seed oil skeptics, who are mistrustful of the health system and crave clarity on how manufactured food impacts our health. It leaves no room to acknowledge that maybe vegetable oil isn't the greatest ingredient around.

Bazinet said, while the jury is still out on seed oils, some people may want to take extra precautions. Smokers, who are already under extra inflammatory stress, could perhaps be at elevated risk of health issues from consuming seed oils since their blood won't have as much capacity to oxidize fats.

For most people, the same advice you've heard for decades still holds true.

Eat a diet rich in whole grains, nuts, and vegetables. These polyphenol powerhouses are dream nutrients for your body. Prioritize olive oil — it's low on omega-6 but high in nonessential omega-9, and great for inflammation and brain health. Routinely add in foods that are rich in omega-3, like chia seeds, flax, or fatty fish.

Because here's the thing: If you avoid processed foods that are loaded with sugar, calories, and yes, probably have "seed" oil in them too, all nutritionists would consider that a win.