What’s the truth about seed oils and your health?

Seed oils have been labeled “the Hateful Eight” by critics, who say they’re harmful to your health. But are they as bad as claimed?

“Big takeaway – everything in moderation,” said Brittany Grigorenko, RD, a clinical dietitian at Cape Cod Hospital in Hyannis.

Seed oils include those made from corn, canola, sunflower, cottonseed, grapeseed, safflower, rice bran and soybean. According to a March 1, 2025, Harvard Medical School article, critics claim three problems with them:

1. They are extracted using a toxic solvent called hexane, and traces of the chemical could linger in the finished products.
2. When heated repeatedly, the omega-6 fatty acids seed oils contain can degrade into trans fats and other unhealthy substances.
3. One of these fatty acids, linoleic acid, gets transformed in the body into arachidonic acid, which can result in the production of inflammation-causing chemicals.

In a May 2020 article, online health commentator and author of several books, including ‘Deep Nutrition,’ Cate Shanahan, MD, (known as “Dr. Cate”) wrote that these oils, which are high in polyunsaturated fatty acids, are “disrupting our metabolism and forcing our immune system to produce dangerous levels of inflammation.”

Mixed Effects

These claims blend truth and some false hype, Grigorenko said, and need to be taken into context. For instance:

1. Hexane “can lead to unhealthy side effects, heart disease and other things,” but any traces of it that might remain in processed oils are “so minute” in comparison to the exposure people get from gasoline fumes, she said.
2. Repeated heating of seed oils “can make unwanted components.” This could occur in restaurants that don’t often change the oil in their fryers.
3. “Seed oils have a good fatty acid (omega-3 alpha linolenic acid). They do have some protective properties, as well,” she said. They also contain phytosterols that help control cholesterol levels. Furthermore, according to the Harvard article, research hasn’t shown that omega-6 linoleic acid increases blood markers of inflammation. And an August 2024 American Heart Association piece said both omega-6 and omega-3 fatty acids fight inflammation.

Bottom line is that many of the alternatives to seed oils “contain a lot of saturated fat, which leads to heart disease,” a fact solidly supported by science, Grigorenko said. Butter, beef tallow, lard and other animal fats, as well as palm oil and coconut oil, are all high in saturated fat. Seed oils may not be perfect, but they’re better for you than cooking with those fats, she said.

“No need to get rid of the canola oil that you have,” she said.

Healthier Choices

Healthier choices are extra virgin olive oil and avocado oil, which are not highly processed, Grigorenko said. However, be careful to choose reputable brands and read container labels to see if they have been blended with other plant oils. Be especially choosy when buying avocado oil. A study published October 2020 in Food Control found 82 percent of 22 brands sampled was rancid, blended with other oils or contained no avocado oil.

“If you love butter, try cooking with olive oil and, rarely, butter,” she said.

People need some fat to supply fat-soluble vitamins and other nutrients, she said. Because oils are calorically dense, a little is all that’s necessary. You can cut out a lot of seed oils and trans fats from your diet by avoiding fast food, fried food and highly-processed food, which often contains large amounts of sugar and salt and are packed with calories, Grigorenko said. She gave the example of “gas station muffins” – individually packaged baked goods made with trans fats and additives to keep them moist on the shelf.

“Try to eat healthier overall. We want to eat a variety of foods, as well,” she added.

“Eat around the outside of the grocery store. More whole foods, more plant-based foods.”