The Truth About Seed Oils

I just looked down at the bag of cashews I was pulling my hand out of and noticed that the ingredients listed were: cashews roasted in vegetable oil (peanut, cottonseed, sunflower seed, canola and/or rice bran oil).  Seed oils have been a hot debate over the last few years, mostly thanks to social media.  Seed oils are being blamed for everything from inflammation to weight gain and cancer.  But what does the research say?  Are these oils actually bad for your health?

What are Seed Oils? 

When people talk about seed oils, eight specific types get the most attention: canola, soybean, safflower, corn, cottonseed, grapeseed, rice bran and peanut oils. However, there are a wide variety of seed oils available, including those from sesame, flaxseed and walnut.

What Constitutes the Health Debate? 

Omega-3 vs Omega-6 fatty acids

Seed oils contain different amounts of saturated, monounsaturated and polyunsaturated fats. Polyunsaturated fats, or PUFAs, are often present in high amounts and are the focus of many seed oil debates. PUFAs include omega-3 and omega-6 fatty acids, which may help to decrease inflammation in the body when consumed in appropriate ratios, although research on the ideal ratio is unclear. Most seed oils have a much higher amount of omega-6 fatty acids compared to omega-3s. While omega-3s are anti-inflammatory, the high omega-6 content is highly debated. Omega fatty acids are often categorized as omega-3s are "good" and omega-6s are "bad," but it’s not that simple. There is a lack of valid research to suggest that omega-6 fatty acids cause inflammation. Nevertheless, some scientists link omega-6s to pro-inflammation due to basic biochemistry while experts like those at Stanford Medicine argue for the anti-inflammatory benefits. In addition, a 2025 study showed that major omega-6 polyunsaturated fatty acids are more likely to be anti-inflammatory than pro-inflammatory. Omega-3 fatty acids (found in foods such as fatty fish, walnuts, chia and flax-seeds) are known for their role in supporting brain and heart health. Meanwhile, research suggests that omega-6 fats are beneficial for lowering the risk of heart disease, with recent research suggesting a decreased mortality rate for those who replace butter with plant-based oils, including those from seeds.

How seeds oils are made

Another component of the seed oil debate is about how seed oils are produced. Some oils are expeller-pressed or cold-pressed, meaning that heat or chemicals are not used during the process of oil extraction.  An expeller press is a machine that presses seeds and nuts through a cavity and uses intense friction and pressure to extract oil. During this process, there isn’t any added heat but since the seeds are pressed using friction, heat is created (around 140-210˚ F). Once the seeds are pressed, the oil is removed. Commonly, the seeds remain in the press to form a hard “brick” which can later be used as animal feed. When expeller pressing, it takes a large number of nuts or seeds to create a high yield – which means more money. This is one of the biggest reasons why oil manufacturers aren’t keen on using this method of extraction and instead use methods that include chemicals and high heat. When pressing seeds or other ingredients to create cold-pressed oils using an oilseed press, less heat is used. The seeds or ingredients are placed in the press and then are crushed by the machine to obtain the oil. Typically, when these ingredients are pressed, they are at a much lower temperature (122˚ F) compared to an expeller press. Since these oils are pressed at a lower temperature, they retain their unrefined healthy antioxidants.

Unfortunately, seed oils are produced in small batches, can have a cloudy appearance and can go rancid quickly. In order to yield a clear, shelf-stable oil, producers use heat in extracting the oil from the seed. The moment high heat is introduced into the process is when the oil loses many of its antioxidants and vitamins. This is commonly seen in “refined” oils which are made by using high temperatures and chemicals, such as hexane, to extract a high yield in a short period of time. Concerns exist about the potential for chemicals to remain in oils after processing. However, multiple regulatory reviews and exposure assessments consistently find that residual hexane (the main solvent used in seed oil extraction) is extremely low in refined oils—typically far below safety limits, even in high consumers of dietary fat.

So, Should Seed Oils Be Avoided or Not?

As with anything in nutrition, it’s nuanced!  It’s important to consider a variety of factors when choosing what to eat. Top sources of seed oils for many Americans come from ultra-processed foods, such as baked goods, chips, frozen meals, convenience items and fried food, which lack nutrition benefits.  While these foods can be enjoyed in moderation, many Americans still struggle with consuming these foods too frequently; which may be due to a poor relationship with food, financial restraints, or lack of understanding of nutrition.  If you find a seed oil listed in the ingredients of foods like whole-grain bread, peanut butter, or nuts (like my cashews), review the other nutrition facts about that food to see if the food provides other beneficial nutrients. Using seed oils to prepare wholesome food at home can be beneficial to your health, especially when they are used to replace too much saturated fat. In general, eat packaged dessert and snack items more sparingly, which may contain seed oils and lack in nutrition. However, if you’re eating nutrient-dense foods, such as nut butter and whole-grain breads, that contain seed oils, the benefits outweigh the non-evidence based risks.  

What Oil Should You Cook With?

Seed oils such as grapeseed, canola and soybean (labeled as vegetable) have a high smoke point, which means they don’t degrade during cooking. In addition, they are good substitutes for solid fats like butter, lard or shortening, which contain more saturated fats.  Extra virgin olive oil produces fewer harmful oxidation products when heated, it remains chemically stable even during sautéing and moderate frying, and the high antioxidant content protects it from breakdown. Refined avocado oil consistently ranks highly in both nutrition and chemistry research because of its very high smoke point (~500°F+), high MUFA content, and low oxidation rate under heat.  Here are some easy ways to use more of these oils and include more healthy fats into your diet:

• Substitute for some of the solid fat in baked goods

• Season a cast iron skillet

• Oil grill grates to keep food from sticking

• Roast vegetables in the oven

• Stir-fry meat and vegetables

• Pop popcorn on the stove

• Make salad dressings — the fat in oils increases the absorption of the fat-soluble vitamins A, E and K that are in leafy greens.