By now, you might have heard that seed oils are bad for you — if not from social media wellness influencers, then from Health Secretary Robert F. Kennedy Jr. himself.
Kennedy has said these vegetable oils — extracted from the seeds of plants, like canola, soybean and safflower — are poisoning Americans and driving the obesity epidemic. Part of the evidence he points to is that obesity rates started to rise as seed oils began to dominate the American diet.
Many nutrition and health researchers say that while seed oils might not be as good for you as olive oil, claims that they're harmful to health have been stretched too far.
"This is one of the more studied topics in nutrition. So it's sort of extra bewildering to quite a few of us in the field that this is coming up," says Christopher Gardner, a nutrition scientist and professor of medicine at Stanford University.
He says studies have consistently shown that replacing saturated fats, such as lard or beef tallow, with fats from plant oils leads to better health outcomes.
Still, Kennedy celebrated when the fast-food chain Steak 'n Shake announced earlier this year that it would stop making its french fries with seed oils and use tallow — rendered beef fat — instead.
When we reached out to Secretary Kennedy, his team pointed us to the MAHA report, which says that seed oils contribute to imbalances of fatty acids that play "a potential role in inflammation."
So what is the science on seed oils? Let's unpack some of the criticisms.
Refining with chemicals and heat
Seed oils — commonly called vegetable oils — are extracted from the seeds of plants.
Critics tend to focus on eight specific oils, sometimes referred to as the "hateful eight": soybean, canola, corn, cottonseed, sunflower, safflower, rice bran and grapeseed.
To maximize how much oil is drawn out of these seeds, manufacturers usually process them using heat and chemicals, explains Eric Decker, a professor emeritus of food science and lipids researcher at the University of Massachusetts Amherst. It's a cheaper and more efficient process than mechanically pressing the oil out. By comparison, extra virgin olive oil is squeezed out of the fruit without the help of chemicals or heat.
Decker says critics often raise concerns about the most commonly used solvent in refining seed oils — hexane — which is hazardous. The hexane is removed during processing, "but you end up with very small amounts left in the oil," he says.
However, Decker says these residues are at levels too low to be toxic. A toxicology report from the federal government, published in April 2025, called the amount "toxicologically insignificant." And any residual hexane is likely to evaporate once you heat your oil during cooking, Decker says.
Caitlin Dow, a senior nutrition scientist with the Center for Science in the Public Interest, says she's personally not concerned about hexane residues in seed oils, but if you are, you can always buy organic seed oils — they aren't processed with hexane, but they do cost more.
Do seed oils promote inflammation?
One common argument against seed oils is that they promote inflammation — a physiological response that helps the body heal from infection or injuries. President Trump's nominee for surgeon general, Dr. Casey Means, has written that seed oil "increases inflammation in the body." Too much inflammation over a long period of time — chronic inflammation — can lead to health problems like autoimmune diseases, heart disease and certain cancers.
This idea is rooted in the kinds of fats found in these oils, says Sarah Berry, a professor of nutrition at King's College London.
Seed oils tend to have higher levels of essential fatty acids called omega-6s and lower levels of other essential fatty acids called omega-3s. These fatty acids play a role in lots of different body processes, including regulating inflammation. Berry says our bodies tend to convert omega-3s into chemicals that fight inflammation," while omega-6s can be converted into chemicals that promote inflammation.
That's why critics say you shouldn't eat seed oils that are high in omega-6s, because they argue that this will promote chronic inflammation.
Berry says that might make sense in theory, "but it doesn't play out in real life, it doesn't play out in the human body."
Berry says randomized controlled trials have found that, when people consume more seed oils, they don't show signs of excess pro-inflammatory compounds in their tissues, and they don't have more markers of inflammation.
There's also strong evidence that omega-6s help lower levels of bad cholesterol, which reduces the risk of heart disease, which is why the American Heart Association supports eating them as part of a healthy diet.
One researcher who has spent decades studying fatty acids is Tom Brenna of the University of Texas at Austin. He is concerned that some people may be eating too many omega-6s in their diet from seed oils, because not everyone processes omega-6s in the same way. He says emerging research suggests some people may be more susceptible to inflammation from omega-6s.
The omega-6 & omega-3 balance
Most Americans eat about 10 times more omega-6 fats than omega-3 fats. And all the nutrition researchers we spoke with agree that for better health, it's a good idea to bring that intake into better balance, although the exact ratio has not been defined, according to the National Institutes of Health.
Since most people get plenty of omega-6s in their diet, the general advice is to up your intake of omega-3s. Fatty fish like salmon, mackerel and sardines, and plants including walnuts, flaxseeds and chia seeds are all rich sources of omega-3s.
And Brenna says you shouldn't stop eating omega-6s altogether.
"Some of the influencers are talking about getting rid of all the omega-6 in the diet," Brenna says. "And that would be a terrible idea," he says. "Some omega-6 is absolutely required. The question is how much?"
Brenna says he sticks mostly to olive oil — which is a fruit oil — though he notes that if everyone only used olive oil, "there isn't enough olive oil in the world" to meet demand. And he says it's expensive.
Another option: use seed oils labeled as "high oleic." These oils have lower levels of omega-6s and fatty acid profiles similar to olive oil.
Nutrition scientist Caitlin Dow is not worried about seed oils. She has a bottle of canola oil in her pantry. On a recent afternoon, she was using it to stir-fry vegetables — bell peppers, zucchini, carrots and broccoli.
"I don't want people afraid to use seed oils thinking that they're doing something bad for their health or their family's health," she says. "They're not doing anything bad. It's a much healthier option than switching to lard or butter or coconut oil."
One thing to keep in mind when using vegetable oils is that you should avoid repeatedly reheating the same oil at high temperatures, like you might do with a deep fryer — which are common in restaurants and fast-food chains. Over time, that can lead to changes in the oil that can promote inflammation in the body.
But the take-home message here, Decker says, is to eat less fried food. "In general, fried foods don't really represent a healthy category that we should be eating on a regular basis."
And that brings us to ultra-processed foods
The main reason why our seed oil consumption has increased dramatically is because these oils are ubiquitous in ultra-processed foods, which now dominate the U.S. food supply.
And one thing everyone seems to agree on is that Americans should eat fewer ultra-processed foods, which tend to be high in sugar, salt and unhealthy fats, as well as preservatives, artificial dyes and other additives. There is lots of evidence that shows eating too much ultra-processed food is linked to poor health outcomes.
"So many of the seed oil haters show these beautiful graphs showing how, as intakes of seed oils have increased over the years, so have rates of all of these awful chronic diseases – cancer, cardiovascular disease, Type 2 diabetes, obesity," Berry says. "But look what else has changed. Our food landscape is almost unrecognizable now compared to how it was 50 years ago."
Berry and Gardner say you can't single out seed oils for this correlation when ultra-processed foods are often high in other ingredients known to drive poor health.
"Is it the junk food that's causing these health issues or is it the seed oils? And I have always thought it's the junk foods," Gardner says.
Instead of focusing on which oils you eat, Gardner says focus on your overall diet. Gardner, Berry and Brenna all agree that means cutting back on ultra-processed foods and cooking at home more. And make sure to get plenty of fruits, vegetables, legumes, nuts and seeds and omega-3s from foods like fish.
And if you use some seed oil to make a salad dressing that encourages you to eat more vegetables, Gardner says — that's a win for health.
NPR requested an interview with Secretary Kennedy for this story but did not hear back.
Edited by Jane Greenhalgh
Copyright 2025 NPR
