Are Seed Oils Bad for You? Here Are the Facts

If you’re confused about seed oils, you’re not alone. Social media is packed with videos from people who claim that seed oils are toxic. They blame these oils for increasing rates of obesity, Type 2 diabetes, and more.

The nomination of Robert F. Kennedy Jr. to be the incoming head of the Department of Health and Human Services has drawn more negative attention to seed oils. In an October Instagram post, Kennedy called seed oils “one of the driving causes of the obesity epidemic.” He claimed that Americans are being “unknowingly poisoned” by them. 

Many experts in the medical and nutrition communities say that these claims are overblown, and that these oils can be part of a healthy diet. Here’s what you need to know about seed oils, and what the data shows. 

What are seed oils, and what are they made with?

Seed oils are vegetable oils that are extracted from the seeds of plants, says Christopher Gardner, PhD, a professor of medicine at Stanford University. Some of the most common seed oils have been dubbed the “Hateful Eight” by wellness influencers on social media:

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

The oils are typically made from crushed seeds, although each is slightly different, says Scott Keatley, RD, co-owner of Keatley Medical Nutrition Therapy. Canola oil is derived from the seeds of the canola plant, which is a type of rapeseed, he says. Rapeseed is a flowering plant with oil-rich seeds.

“Grapeseed oil, as the name suggests, is made from the seeds of grapes, typically as a byproduct of winemaking,” says Keatley. “Soybean oil comes from crushed soybeans and is one of the most widely used oils in the United States.”

Generic vegetable oil is often a blend of different seed oils like canola, sunflower, and soybean. It’s important to note that olive oil and avocado oil are not seed oils. Extra-virgin olive oil is made from the fat pressed from whole olives, while avocado oil is pressed from the pulp of avocados. 

What are the benefits of using seed oils?

Seed oils are often used as a substitute for animal fats in cooking, says Gardner. However, “all of these have less saturated fat than butter or lard,” he says. For example, one tablespoon of canola oil contains about one gram of saturated fat. Butter contains seven grams of saturated fat per tablespoon.

“There is well established evidence that replacing saturated fat with unsaturated fat in the diet, such as replacing butter, lard, or tropical oils [like palm or coconut], with all types of non-tropical, plant-based oils, including seed oils, leads to LDL-cholesterol lowering and cardiovascular benefits,” says Gardner. LDL cholesterol is considered “bad” cholesterol.

Cooks often reach for seed oils for three main attributes: a relatively high smoke point, a neutral flavor, and a lower cost. 

Relatively high smoke point 

Oils reach their smoke point when they begin to break down and emit smoke. When this happens, they may release chemicals that give food a burned or bitter flavor, as well as free radicals that can harm the body, says Keatley. A possible benefit of seed oils is that “their smoke points are relatively high,” he says. 

For example, safflower oil has a smoke point of 510°F, while rice bran, sunflower oil, and soybean oil have smoke points of 450°F. Canola oil’s smoke point is approximately 400°F. 

Butter has a significantly lower smoke point, at 302°F, and extra-virgin olive oil has a smoke point of 320°F. That’s why seed oils like canola are often used to fry, sauté, or help with other forms of high-heat cooking. 

Neutral flavor

Seed oils are preferred for their neutral flavor that won’t overpower other ingredients in a recipe. “Canola oil, with its neutral flavor and versatility, works well for baking, sautéing, and frying,” says Keatley. “Grapeseed oil’s light flavor makes it perfect for salad dressings, marinades, and cooking at lower-to-medium heat. Soybean oil is suitable for roasting, frying, and baking, and it’s often used in emulsified dressings like mayonnaise.”

Affordability

Seed oils tend to be less expensive than extra-virgin olive oil, butter, and other types of cooking fat. 

Why are people concerned about seed oils?

Many seed oil naysayers focus on two elements: the potential presence of hexane, a chemical that’s used commonly as a liquid solvent to extract oils from the seeds, and the unsaturated fat content of the oils themselves.

Hexane is considered toxic in gas form, but should fully evaporate after the oil extraction process. (Seed oils can also be made by a mechanical process, but these versions are usually more expensive and less popular.) The Food and Drug Administration (FDA) doesn’t measure hexane residue in cooking oils, so it’s not clear if trace amounts of hexane may still be present in seed oils.

The other potential sticking point to some is the high concentration of omega-6 polyunsaturated fats in these oils. According to detractors, the omega-6 fatty acids found in seed oil, especially linoleic acid, can cause chronic inflammation.

So, are seed oils bad for you?

The American Heart Association (AHA) released a statement in 2017 that supports the use of omega-6 fatty acids like seed oils in a healthy diet. 

According to the AHA, omega-6 is a polyunsaturated fat that the body needs, but it can’t produce on its own — it must come from foods. Polyunsaturated fats like omega-6s help the body reduce the level of bad cholesterol, and lower the risk for heart disease and stroke, per the AHA. The organization states that “there’s no reason to avoid seed oils and plenty of reasons to eat them.”

“Canola and soybean oils contain omega-3 and omega-6 fatty acids, essential fats that may play roles in reducing inflammation and supporting brain health when consumed in a balanced ratio,” says Keatley. “Additionally, these oils are a good source of vitamin E, a powerful antioxidant that may help protect cells from damage caused by oxidative stress.”

Mainstream research hasn’t linked seed oils to the claims made by critics. A scientific analysis of research published in 2017 found that linoleic acid did not have a significant effect on inflammatory markers in the blood. The researchers stated that only a small amount of omega-6s are converted into arachidonic acid, a precursor for compounds that counteract inflammation in the body. 

A study published in 2023 in the International Journal of Molecular Sciences found that people who have more omega-6 fatty acids in their blood were more likely to have better cardiovascular health and glucose metabolism, which is the ability to convert blood sugar into energy. And a new peer-reviewed scientific paper published in the British Journal of Nutrition determined that linoleic acid lowers the risk of cardiovascular disease and Type 2 diabetes. 

Downsides of seed oil 

Keatley stresses that seed oils aren’t perfect. “Overheating these oils past their smoke points may degrade them, leading to the formation of harmful compounds such as acrolein, aldehydes, and polycyclic aromatic hydrocarbons,” he says. 

“These substances may irritate the respiratory system, promote inflammation, and, with long-term exposure, potentially increase the risk of chronic diseases like cancer or cardiovascular issues,” he adds. While that’s the case with all cooking oils, “it is more likely to happen with seed oils — mono/polyunsaturated oils — over more saturated fats/oils,” he says. 

Gardner says you’re fine to cook with seed oils. “I recommend people cook with oils they can afford and that are as minimally processed/refined as possible, with an exception. Some of the processing is done to avoid problems with smoke point, which can be beneficial,” he says. 

Rather than obsess over seed oils, Gardner suggests to pay attention to the food you’re cooking with the oils, such as vegetables and high-quality proteins. “Assuming [you] are only using a tablespoon or two for cooking, it likely won’t make much difference if it is sunflower, safflower, canola, avocado, corn, or soybean oil,” he says. 

The bottom line? Research hasn’t shown seed oils to be bad for you, but you should pick the oil that you — and your wallet — find most suitable.