Seed oils, a common component of the modern diet, have become a topic of considerable debate in the health and nutrition community. This article aims to explore the benefits and risks associated with seed oil consumption, drawing on scientific research and expert opinions to provide a comprehensive overview.
What are Seed Oils?
Seed oils are vegetable oils extracted from the seeds of plants. This category includes commonly used oils like sunflower oil, canola oil (derived from rapeseed), soybean oil, corn oil, safflower oil, and grapeseed oil. These oils are prevalent in various food products, from home-cooked meals to processed snacks, making them a significant part of the average diet.
Christopher Gardner, PhD, the director of nutrition studies at the Stanford Prevention Research Center, has studied the effect of dietary changes - including oils and fats - on health for more than three decades. We asked Gardner, the Rehnborg Farquhar Professor, what an average American should know about seed oils and their effects on health.
The Argument Against Saturated Fats
For decades, dietary guidelines have emphasized the importance of replacing saturated fats with unsaturated fats to improve cholesterol levels. As a graduate student in 1995, Gardner analyzed more than a dozen studies on the effects of different types of dietary fats on cholesterol levels. Like many researchers before him, Gardner found that people who switched from using mostly saturated fat in their diets to eating more unsaturated fats saw their LDL cholesterol levels decrease. "Every study for decades has shown that when you eat unsaturated fats instead of saturated fats, this lowers the level of LDL cholesterol in your blood," Gardner said.
Saturated fats, commonly found in animal products like butter, cheese, and meat, as well as tropical oils like coconut and palm oil, can raise LDL cholesterol levels, increasing the risk of heart disease. Unsaturated fats, including those found in seed oils, can have positive health effects when consumed in moderation as part of a balanced diet.
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Omega-6 Fatty Acids and Inflammation: Unpacking the Concerns
Much of the recent criticism of seed oils centers on their omega-6 fatty acid content, with claims that these fatty acids promote inflammation. Omega-3 and omega-6, both found in fish, seeds, and nuts, are essential fatty acids, meaning our bodies require them but cannot produce them. So we must get them through our diets. "The omega-3s seem to be a little more anti-inflammatory than the omega-6s," Gardner said. "But somehow, this has been flipped into saying the omega-6s are pro-inflammatory. That isn't the case. For decades, Gardner has hoped to find links between diet and inflammation but he said the immune system is still too poorly understood to make these kinds of associations when studying humans. So he is immediately skeptical of claims that seed oils cause inflammation - the body's natural immune response to injury, infection or stress. "Measuring inflammation with any current laboratory tests is incredibly complex and just can't be done yet," he said.
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.
While omega-6 fatty acids can be converted into chemicals that promote inflammation, studies have not shown that consuming seed oils leads to excess pro-inflammatory compounds in the body. In fact, there is strong evidence that omega-6s help lower levels of bad cholesterol, reducing the risk of heart disease. The American Heart Association supports eating them as part of a healthy diet.
The Importance of Balancing Omega-3 and Omega-6
Most Americans consume about 10 times more omega-6 fats than omega-3 fats. 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 Tom 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?"
Instead of focusing on eliminating omega-6s, the emphasis should be on increasing omega-3 intake to achieve a healthier balance. 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."
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Processing Methods and Potential Concerns
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.
While concerns about chemical residues in seed oils exist, experts like Caitlin Dow say they are 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.
Seed Oils and Ultra-Processed Foods
The rise in seed oil use and consumption has paralleled increases in obesity and chronic disease. But Gardner said this correlation could be caused by other factors. Diets high in ultra-processed foods, for instance, are associated with cardiovascular disease, diabetes, and many other health conditions, and these ultraprocessed foods often contain seed oils. "It's true that we eat more ultra-processed junk food than we ever have before," he said. "If you cut out seed oils by avoiding McDonald's and cake and chips, you're probably going to feel great," he said.
Seed oils are frequently used in processed and ultra-processed foods, including fast food, packaged snacks, and frozen meals. These foods are often 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. 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 solely on seed oils, experts recommend focusing on overall diet and reducing the consumption of ultra-processed foods.
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Practical Considerations for Seed Oil Use
When choosing what fat to use in cooking food, Gardner stresses that using vegetable oil instead of an animal-based fat is best for cholesterol levels. While it may be preferable to cook with olive oil - a key component of the Mediterranean diet, which studies have consistently associated with a lower risk for cardiovascular disease - that's not going to add the right flavor to every type of food, Gardner said. "And if it means that because you did that, that you're going to have the veggie stir-fry and the salad and you're going to eat more of it because of the flavor? Fantastic," he said. "The seed oils are not killing you.
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.
Alternatives to Seed Oils
Instead of using seed oils at home, Zumpano suggests doing most of your home cooking with oils that are high in heart-healthy omega-3 fatty acids instead of piling on the omega-6s:
- Extra-virgin olive oil (EVOO) for low-heat cooking
- Avocado oil for high-heat cooking
“Both of these oils are clinically shown to have higher monounsaturated fats,” Zumpano shares. “They’re not seed-based, and they don’t go through the same type of processing, so they’re very unrefined and even have a lot of nutritional benefits.”