Recently, seed oils like canola, soybean, sunflower, and corn oil have come under fire in popular media and wellness circles.
The claims? That these oils are toxic, cause inflammation, contribute to heart disease, and should be avoided at all costs. But are these claims grounded in science, or are they myths that have been blown out of proportion?
Let’s take a closer look at some of the most common misconceptions about seed oils and set the record straight.
But first… What exactly are seed oils?
Seed oils are cooking oils that have been extracted from plants and, like all dietary fats, are composed of monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs), and saturated fatty acids (SFAs). Polyunsaturated fats, or PUFAs, include omega-3 and omega-6 fatty acids, which are essential fatty acids, meaning that our body needs them but can’t produce them, so we must consume them through our diet. However, many have come to demonize the omega-6 content of common seed oils, with social media influencers terming them as the “Hateful Eight.”
This “Hateful Eight” includes canola (rapeseed), corn, cottonseed, soybean, sunflower, safflower, grapeseed, and rice bran oils. However, other seed oils include flaxseed, chia seed, and hempseed. So, why is everyone saying these oils are bad and should be banned from your kitchens? Let’s get into it.
Myth 1: Seed Oils Are Bad for Heart Health
One of the most persistent myths is that seed oils, which are high in polyunsaturated fats (especially omega-6 fatty acids), are bad for your heart. Some critics claim that these oils contribute to inflammation and increase the risk of heart disease.
The Truth: Research suggests replacing saturated fats (like those found in butter or lard) with polyunsaturated fats, including omega-6 fatty acids, can improve heart health. Studies have shown that diets high in unsaturated fats (like those from seed oils) can reduce the risk of cardiovascular disease. A 2021 meta-analysis looked at the relationship between omega-6 supplementation and cardiovascular disease and found that omega-6 intake did not affect risk for cardiovascular morbidity or mortality, though more research is still needed. Research on omega-6 fatty acids and cardiovascular disease is complex, and more studies need to be done to clarify the relationship between the two. However, choosing polyunsaturated fats over saturated fats, including seed oils, is better.
It's important to consider that it's not just the omega-6 fats that matter, but the balance of omega-6 to omega-3s in your diet. Western diets tend to be disproportionately high in omega-6 and low in omega-3s, which may contribute to chronic diseases such as heart disease. So, it's essential to balance your intake by consuming more omega-3-rich foods like fatty fish, flaxseeds, and walnuts alongside seed oils. Incorporating seed oils such as flax, hemp, and chia oil will give you some extra omega-3s and are perfect for salad dressings, cold sauces, or drizzling over pasta or vegetables! Adding these whole seeds (flax, hemp, and chia) into your diet will provide the omega-3 benefits and increase your fiber intake, which is also important in supporting cardiovascular health. Sprinkle them over your salads or oatmeal or add them to your smoothies or yogurt!
Myth 2: Seed Oils Cause Inflammation
Many people believe that omega-6 fatty acids—found in abundance in seed oils—promote inflammation in the body. The culprit they’re referring to is a specific omega-6 fatty acid known as linoleic acid and its conversion into arachidonic acid. This may contribute to the chronic overproduction of signaling molecules known as eicosanoids, which play a role in the inflammation process in our body.
The Truth: There is evidence that linoleic acid can be converted to arachidonic acid and its role in increased inflammation and blood pressure. However, there are essential factors to consider. The first is recognizing that we don’t live in a controlled laboratory environment nor in Petri dishes in real life. Research demonstrating the link between linoleic acid and inflammation has been done on lab animals or in petri dishes. There are simply no compelling human clinical studies to support the theory that seed oils are causing the chronic inflammation problem we have today.
In fact, several studies have shown the opposite. A 2021 review found increasing intake of arachidonic acid (up to 1500 mg/day) had no adverse effect on immune function and markers of inflammation. Another meta-analysis investigating the effect of increasing dietary linoleic acid on inflammatory markers in the blood found no significant impact. This is likely because only a small percentage of dietary omega-6s is converted to arachidonic acid.
Most studies that have linked omega-6 to inflammation focus on excessive omega-6 intake without a corresponding increase in omega-3s. In fact, the body needs both omega-6 and omega-3 fatty acids in a balanced ratio to maintain a healthy inflammatory response. When consumed in moderation and balanced with omega-3s, omega-6s from seed oils like sunflower, safflower, and canola oil are not inherently inflammatory.
The other consideration to the idea that these dangerous seed oils cause inflammation and chronic disease is the food sources we’re getting them from. If your diet is broadly made up of fried foods, chips, and bakery items, you are consuming seed oils and foods high in fat, salt, and sugar, aka ultra-processed foods. It’s crucial to differentiate seed oil from the highly processed and low-nutrient content of certain types of food.
Omega-6 fatty acids can contribute to inflammation, but this doesn’t mean consuming them in moderation is harmful. Omega-6s are essential fats our body needs for many important functions, including cell membrane structure and hormone production. And just like everything else in life, the key is balance!
If you’re focused on reducing inflammation, the best thing to do is aim for an overall healthy diet rich in antioxidants, healthy unsaturated fats, and fiber and low in processed foods. A good rule of thumb is the 80/20 rule-- focus on eating whole foods, including fruits, vegetables, lean protein, nuts, and seeds, 80% of the time while enjoying the occasional indulgent meal of your favorite fried food or dessert 20% of the time.
Myth 3: Seed Oils Are Full of Toxic Trans Fats
Another widespread myth is that seed oils contain high levels of trans fats, which are harmful to health. Trans fats have been strongly linked to heart disease, and some argue that all processed oils—especially those used in frying—are loaded with them.
The Truth: While some industrially processed seed oils can contain small amounts of trans fats, the levels in most commercially available oils are very low—far below the levels that would pose a significant health risk. The genuine concern with trans fats arises from partially hydrogenated oils, a byproduct of industrial processing.
Cold-pressed or unrefined seed oils, such as extra virgin sunflower or canola oil, contain virtually no trans fats. When you choose minimally processed oils or oils labeled as "non-hydrogenated," the risk of consuming harmful trans fats is negligible. Also, home cooking with these oils (rather than frying at high temperatures for extended periods) minimizes the formation of trans fats.
Myth 4: Seed Oils Are Highly Processed and Unhealthy
Critics often point out that seed oils are refined through high heat and chemical processes, which could make them unhealthy. Some people claim that this processing strips the oils of essential nutrients, making them dangerous to consume.
The Truth: While many seed oils are refined, not all processed oils are unhealthy. Refining removes impurities and extends shelf life, preserving much of the oil’s beneficial fatty acid profile.
It's important to note that not all seed oils are processed the same way. Cold-pressed oils, for example, are minimally processed and retain more of their natural antioxidants and nutrients. These are often a better choice if you're concerned about the quality of the oil.
Moreover, an oil's health impact is determined not just by its processing method but also by its overall fat content. Polyunsaturated oils like canola or sunflower oil are heart-healthy when used in place of saturated fats, and they provide essential fatty acids that the body needs for cell function.
Myth 5: Seed Oils Are Only Used for Deep-Frying and Fast Food
There's a common belief that seed oils are primarily used in deep-frying or processed foods and are, therefore, inherently unhealthy.
The Truth: While seed oils are indeed commonly found in fast food and processed snacks, they are also versatile cooking oils that can be used in everyday cooking, salad dressings, and even baking. In fact, because of their high smoke points, oils like canola, sunflower, and grapeseed oil are excellent for stir-frying, grilling, and sautéing. Additionally, their more neutral flavor compared to oils such as extra virgin olive oil (EVOO) or coconut oil may be a better option when baking your favorite treats.
Seed oils can be a healthy choice in moderation and when used as part of a balanced diet. The real problem arises when we consume excessive amounts of highly processed foods loaded with these oils, often alongside other unhealthy ingredients like refined sugars and preservatives. Additionally, it’s important to stress that any oil used for deep frying poses extra health risks due to the chemical changes it undergoes when exposed to high heat. Thus, the oil's exposure to high heat is more concerning than the type of oil itself.
Myth 6: All Seed Oils Are the Same
Some people believe that all seed oils are identical regarding health impact. They lump oils like canola, sunflower, soybean, and cottonseed oil into one big “unhealthy” category.
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The Truth: Not all seed oils are created equal. The fatty acid profile varies significantly from one seed oil to another. For example:
● Canola oil is relatively high in omega-3s (ALA), making it a better option for supporting heart health.
● Flaxseed oil is a powerhouse of omega-3s, making it great for anti-inflammatory purposes.
● Sunflower and safflower oils are higher in omega-6s, but these can still be part of a healthy diet when balanced with omega-3s.
Each type of seed oil has its unique characteristics, and understanding the specific health benefits (and potential drawbacks) of each one can help you make an informed choice.
Final Thoughts: A Balanced Approach to Seed Oils
The bottom line is that seed oils are not the dietary villains they’re often made out to be. In fact, when consumed in moderation and as part of a well-rounded diet, seed oils can contribute to a healthy intake of essential fats that support heart health, brain function, and overall well-being. In addition, they are often a more budget-friendly option and offer versatility when cooking and baking at home.
If you’re concerned about the potential risks of processed seed oils, consider choosing cold-pressed or unrefined oils, which retain more nutrients and antioxidants. And remember, the key to a healthy diet is balance—so instead of vilifying one ingredient, focus on the quality of your overall food choices and strive for a diverse range of healthy fats, including those from whole foods like avocados, nuts, seeds, and fatty fish.
By separating fact from fiction, you can make informed decisions about what’s best for your health and debunk the myths surrounding seed oils for good.
Cate Brotman, MS and Oregon Health and Science University Dietetic Intern class of 2025 wrote this article. It was reviewed for accuracy and edited for clarity by Cary Cuevas, RDN, LD, CPT.
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