Imagine wandering into a room where people are arguing about whether “things” are good or bad for you. Confused, you might ask, “What things are you talking about?”
“Oh, you know,” someone replies. “Things. Cars. Hornets. Hugs. Rusty barbed wire.”
To make accurate judgments, we need a lot more specificity and context. That’s especially true of one of the loudest and most rancorous debates in the wellness world these days: the effects of seed oils on human health. As you’ll see, many very different substances are being lumped together in one category — a shortcut that makes rational discussion impossible.
Some folks thought the debate had been settled decades ago when governments encouraged the food industry to replace animal fats with “heart-healthy” alternatives like canola, soybean, and sunflower oil. Lately, however, these vegetable oils have come under fire from critics who claim they contribute to inflammation, chronic disease, and obesity.
At the same time, animal-based fats, including beef tallow (a rendered form of animal fat largely phased out of mainstream cooking decades ago), are experiencing a revival.
Advocates argue that animal-based fats are more “natural” than processed seed oils and, therefore, healthier.
In this article, we’ll cut through the controversy surrounding seed oils. We’ll examine the health claims against seed oils, explore if seed oils might have any benefits, and look at the healthiest ways to cook.
What Are Seed Oils?
Seed oils are refined and processed oils made from the seeds of plants. All seed oils are vegetable oils, but not all vegetable oils are seed oils. Olive, avocado, palm, and coconut oils are examples of vegetable oils that come from fruits, not seeds.
Seed oils are widely used in cooking and in processed and fast foods. The seed oils most commonly used for these purposes are canola (also known as rapeseed), corn, cottonseed, grapeseed, soybean, sunflower, rice bran, and peanut oils. Dr. Cate Shanahan, a vocal critic of these oils, dramatically refers to them as the “hateful eight.”
Other seed oils, used in smaller quantities for flavor or their potential health benefits, include flaxseed, black seed, pomegranate seed, walnut, and sesame oils. These are more often cold-pressed or minimally processed, and may retain more of their natural nutrients.
How Are Seed Oils Made?
Most commercial seed oils undergo a two-step extraction process:
- Mechanical extraction, often via expeller pressing
- Chemical extraction, typically using hexane, a solvent derived from petroleum, to increase yield
After extraction, many oils undergo refinement, known as RBD: Refined, Bleached, and Deodorized. These steps are designed to remove impurities, odors, and pigments, resulting in a clear, neutral-tasting oil that’s stable for high-heat cooking and long shelf life.
- Refining: High heat or steam, sometimes with chemical additives, is used to purify the oil.
- Bleaching: Bleaching clay is added to absorb pigments and reduce color.
- Deodorizing: Steam or heat neutralizes strong smells or flavors.
While this level of processing is standard for many cooking oils on the market, not all seed oils go through these steps. Cold-pressed or unrefined seed oils skip chemical solvents and RBD processing, resulting in oils that may offer more flavor and nutritional value. However, they’re also less stable and more perishable.
The Health Claims Against Seed Oils
So, what are the health risks of consuming seed oils? Critics make three main claims:
- High in Omega-6 Fatty Acids — Seed oils are rich in omega-6 fats, which can promote inflammation when consumed in excess, especially in relation to omega-3 intake.
- Harmful Processing Methods — The RBD process, involving high heat, chemical solvents, and deodorization, may degrade the oil and produce harmful byproducts. Cooking with these oils at high temperatures can potentially make them even more damaging.
- Linked to Chronic Disease — Some believe that regular consumption of seed oils contributes to conditions like heart disease, obesity, and type 2 diabetes.
Let’s look at the evidence related to each of these claims.
Claim 1: Inflammatory and High in Omega-6 Fatty Acids
The real problem with omega-6 fatty acids in seed oils is when they have an unbalanced relationship with another category of essential fatty acids, the omega-3s. (This is starting to sound like a sorority movie about singing groups.)
Omega-6 and omega-3 fatty acids work together to regulate inflammation in the body. While a 1:1 ratio is sometimes cited as ideal, most experts agree that a ratio of up to 4:1 in favor of omega-6s is still considered healthy. The real trouble starts when that balance tips too far, which spells bad things for your health.
Unfortunately, it’s estimated that the average ratio in the US is around 16:1, largely due to the fatty acid composition of seed oils found in processed foods. But that’s not the whole story.
It turns out that different seed oils have quite different omega-6 to omega-3 ratios. As you can see in the following chart of the so-called “hateful 8”, some of the seed oils are astronomically lopsided in favor of omega-6s. But others — notably soybean and canola — are much more balanced. Canola oil, at 2:1, and soybean oil, at 8:1, are in the healthy ballpark. And don’t forget about hempseed oil, which is 3:1, and flaxseed oil, which actually pushes in the other direction, with a 5:1 omega-3 to omega-6 ratio!
A couple of nuances often get lost amid the shouting. First, while it’s true that an imbalance of omega-6s over omega-3s can be inflammatory, it’s difficult to separate correlation from causation. Most of the omega-6 heavy seed oils in the modern diet are consumed in fried and processed foods. People who eat a lot of these foods are prone to all sorts of problematic health outcomes. So it’s possible (maybe even likely) that other factors in those foods, besides the omega-6 fatty acids in the seed oils, also contribute to inflammation.
Some groups of people may also be more susceptible to the health effects of excess omega-6s than others. Africans, Indigenous Americans, Greenland Inuit, and Latinos tend to metabolize omega-6 fatty acids faster, which can turbocharge inflammation.
In summary, there’s some truth to this claim, but it depends on the seed from which the oil is made. My takeaway: if you’re looking to mitigate the risk of excess omega-6 fatty acids, and you want to consume seed oils, you may want to lean towards flaxseed oil (which should never be heated), hempseed oil, or organic canola or soybean oil.
Claim 2: Cooking & Industrial Processing Makes Seed Oils Harmful
We’ve seen that refined seed oils go through a pretty extensive process just to get them ready for food use. And several chemical byproducts of the refining process are pretty alarming. Let’s take a look.
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Glycidol
One of these chemicals is glycidol, a carcinogen that forms during the deodorizing process in oil refining. It’s genotoxic, which means that it can damage your genes, contributing to the development of cancer. Because of this mechanism of harm, no consumption level of glycidol is considered safe. Basically, any amount is too much. Foods fried in seed oils are some of the worst offenders when it comes to glycidol content.
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3-MCPD
Another potentially toxic chemical contaminant that finds its way into processed seed oils is 3-MCPD (not a Star Wars droid but a colorless liquid whose full name is HOCH2CH(OH)CH2Cl). Palm oils and palm fats are the largest contributors to 3-MCPD in the modern industrialized diet. Although this chemical is not genotoxic, it may still contribute to cancer development.
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Hexane
The third nasty compound found in processed seed oils is hexane, which is derived from the other kind of oil (the fossil fuels that power motors and engines). Used in the refining process, hexane is neurotoxic to humans and has long been listed as a cause of occupational diseases in several European countries.
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Free Radicals and ROS
There are also other harmful compounds that can form if the oils are not heated and cooled properly during processing. These compounds can come from the degradation of nutrients, the formation of toxic chemicals such as acrylamides, and oxidation. This last one reduces the quality of the oil and makes it dangerous to human health.
Once processed seed oils have been cooked, high-heat reheating and microwaving can rapidly break down the unsaturated fatty acids and other nutrients in these oils. This process can create free radicals — unstable compounds that can cause damage to your DNA, proteins, and cell membranes.
Foods cooked in oil heated repeatedly (like in fryer vats that go through multiple batches before the oil is replaced) also increase the presence of reactive oxygen species (ROS), accelerating oxidation.
Again, there’s a lot of truth to the claim that seed oils contain harmful chemicals created during processing. Luckily, small-batch or cold-pressed oils — those that have not undergone the RBD refinement process — may not have all these issues and be significantly less problematic, if not downright healthy for you.
Claim 3: Seed Oils Are Linked to Chronic Diseases
Critics of seed oils cite claims that consumption can cause chronic health conditions, including heart disease, metabolic dysfunction, obesity, and migraine headaches. Let’s see what the evidence says.
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Cardiovascular Disease Risk
A 2018 article reviewed data from lab experiments, animal studies, and human trials. (Our view on the use of animals in medical research is here.) The authors found strong evidence that diets high in omega-6 fatty acids increase the amount of a harmful form of cholesterol called oxLDL, worsen inflammation, promote oxidative stress, and increase atherosclerosis (hardening of the arteries). These can all hasten the development of heart disease.
But remember, not all seed oils are super-high in omega-6s, so their contribution to the risk of heart attack may vary depending on the type. The risk seems to depend on the amounts of omega-6s and omega-3s in the overall diet as well as in the particular oils.
And with every question about whether a food or ingredient is good for you or not, you have to ask: compared to what?
In this case, it turns out that if you replace animal fats and trans fats with polyunsaturated fats like those found in seed oils, you can actually reduce cardiovascular disease risk. A 2021 study found that consumption of canola and corn oil lowered the risk of death compared to butter and margarine.
But just because they’re better than butter and margarine doesn’t mean they’re healthy, or that there’s no risk. Excess butter, margarine, or oil in your diet can be detrimental to cardiovascular health, especially for someone who already has heart disease.
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Seed Oil Consumption and Obesity
Here, too, results are mixed. A 2024 meta-analysis looked at 42 studies and found evidence that rice bran, soybean, and sunflower oils were all associated with weight gain, while sesame oil seemed to lead to weight loss. (The study used canola oil as the standard of measurement, so the other oils were either more or less likely than canola to contribute to weight gain.)
Canola oil has been shown to reduce body weight but does not affect other markers of obesity, such as waist circumference, hip circumference, or waist-to-hip ratio. Safflower oil may reduce the amount of fat stored in the trunk region of the body.
And when combined with other non-seed oils such as olive and coconut, some seed oils may even protect against obesity (at least, according to one study, in rats).
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Type 2 Diabetes
Some seed oils appear to protect against the risk of developing type 2 diabetes, at least compared to alternative fat sources. Soybean, canola, and sesame oils have been associated with lower type 2 diabetes risk than peanut oil, refined and blended plant oil (which typically contains soybean, rapeseed, sunflower seed, and rice bran oils), and lard.
Some seed oils, such as pomegranate, sesame, and sunflower seed oils, show potential therapeutic benefits in managing type 2 diabetes and other metabolic disorders. However, results vary depending on the person’s overall diet and health.
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Migraines
A 2022 study found evidence that consuming oils rich in antioxidants, including vegetable oil, may help reduce the severity of migraines due to their anti-inflammatory and neuroprotective properties. The omega-6 to omega-3 ratio seems to be a factor here as well.
What About GMO Seed Oils?
Many seed oils are bioengineered. Ninety percent of the four most common seed oils — canola, soybean, cottonseed, and corn — are from GMO crops.
The plants are bioengineered mainly to allow farmers to treat them with herbicides such as Roundup that would kill non-GMO plants. This means they absorb and, in turn, deliver some of the weed killer glyphosate, a probable human carcinogen.
Glyphosate may disrupt hormones, alter metabolic processes in the human body, and promote tumor formation.
The best way to protect yourself against this is to avoid canola, soybean, cottonseed, and corn oil unless grown organically or certified non-GMO.
A Word About Canola Oil
Canola oil has some passionate critics who claim that it’s “toxic,” blaming it for everything from inflammation to cognitive decline. But these claims don’t hold up under scrutiny. Most are rooted in outdated concerns or confusion with industrial rapeseed oil, which is high in erucic acid (a compound mostly bred out of modern canola). In reality, canola oil is consistently associated with lower cardiovascular risk compared to animal fats. Of course, it’s highly processed and often genetically engineered, which is why moderation and choosing organic or non-GMO versions make sense. But it’s hardly the supervillain of healthy eating.
Seed Oils vs Beef Tallow and Other Animal Fats
Since many wellness influencers continue to pit seed oils against animal fats like beef tallow, let’s see how they compare.
The Problem With Animal Products
Butter, ghee, lard, bacon grease, and beef tallow have all been used to cook food across cultures. However, these animal products have been shown to trigger inflammation that is detrimental to health.
Animal fats are also high in saturated fats, which are solid at room temperature and are associated with higher LDL cholesterol levels and increased risk of cardiovascular disease.
Although foods sourced from animals are sometimes thought of as more “natural” or closer to what our ancestors may have eaten (a central tenet of the Paleo diet), there’s nothing natural about how most animal products are produced these days in factory farms.
There are also major ethical concerns with these products, including their impact on the environment, human health (including via the creation of antibiotic-resistant bacteria), and the suffering of the animals themselves.
What the Research Says
A significant body of evidence suggests that replacing saturated fats with unsaturated fats, like those found in many seed oils, can benefit heart health.
In a major Cochrane meta-analysis of 15 randomized controlled trials involving over 59,000 participants, researchers found that reducing saturated fat intake led to a 21% reduction in cardiovascular events, especially when the saturated fat was replaced with polyunsaturated fat.
And this isn’t exactly new news. Researchers have known for more than 40 years that saturated fat was associated with increased risk of heart disease.
Starting in the late 1980s and early 1990s, many US fast-food chains began replacing beef tallow (high in saturated fat) with vegetable oils, in line with public health guidance that was aimed at reducing cardiovascular disease.
This change was part of a broader shift in national dietary patterns and public health interventions. And during the decades that followed, between 1990 and 2019, US deaths from heart disease declined by nearly 50%. While many factors contributed to this drop, including improved medical care, reduced smoking rates, and increased awareness of heart disease risks, it’s entirely probable that the reduction in saturated fat consumption played a supportive role.
While this isn’t definitive proof that the fast-food oil swap alone saved lives, it fits into a larger pattern of research showing that replacing saturated and animal fats with unsaturated and plant fats can improve cardiovascular outcomes.
And new research continues to back this up. Most recently, a 2025 study found that higher butter intake was associated with increased total mortality and cancer mortality, while higher intake of plant-based oils was associated with lower total, cancer, and cardiovascular disease mortality.
The Type of Fats Matters
The story is more complicated than “seed oils good, animal fats bad,” however.
For one thing, vegetable oils that are partially hydrogenated are high in trans fats, which might be more harmful to health than animal fats.
As of 2018, the US government banned the use of trans fats in processed foods, although there are still loopholes, including a 0.5-gram reporting limit (less than that per serving is considered zero) and the use of trans fats to coat baking pans.
For another, the source of the seed oil matters.
A 2010 review of seven randomized controlled trials found that seed oils’ impact on heart attack risk depends on the type of oil used. This corroborated an updated analysis of data recovered from an extensive dietary study conducted in the 1970s. In it, researchers examined the effects of replacing saturated fats, such as beef tallow, with seed oils. While this substitution consistently led to lower cholesterol levels, it did not always reduce the risk of death from heart disease.
The research suggests that replacing saturated fats with seed oils with a lower omega-6 to omega-3 ratio, like soybean oil, can lower the risk of heart attacks and cardiovascular mortality. However, when seed oils with a higher omega-6 to omega-3 ratio, such as corn oil, are used instead, the risk of heart disease-related death may increase.
What about non-seed oils like olive and avocado oil? While technically fruit oils, they are often lumped into the broader “vegetable oil” category and deserve special attention. Both are rich in monounsaturated fats — especially oleic acid, which has been linked to lower inflammation, improved cholesterol profiles, and reduced risk of cardiovascular disease.
Avocado oil shares many of olive oil’s benefits, and it’s especially heat-stable, making it a solid option for sautéing or roasting. Both olive and avocado oils also contain beneficial antioxidants and polyphenols that may support brain function and reduce oxidative stress. While more expensive than most seed oils, their nutrient profile and potential health benefits make them worth considering as go-to options when oil is used sparingly in home cooking. For more on olive and avocado oil, see our article here.
Nutritional Benefits of Seed Oils (and Alternative Sources)
Some seed oils (like flaxseed and canola) contain beneficial omega-3s and a favorable omega-3 to omega-6 ratio. Canola oil has the most balanced ratio of the most commonly used oils, while flaxseed oil tilts firmly in the omega-3 direction, boasting five times more omega-3 than omega-6.
All seed oils also contain polyunsaturated fats, which are generally healthier for you than saturated fats. (Note: you can also get these healthy fats from whole foods, such as flaxseeds, chia seeds, walnuts, and other foods.)
Some seed oils contain beneficial compounds called tocopherols, including vitamin E. (Again, you don’t need to rely on oil for these nutrients; many whole plant-based foods contain vitamin E.
And losing excess weight is typically easier if you prioritize getting your nutrients from whole foods rather than processed oils. That’s because oil is the most calorically dense food, delivering roughly 4,000 calories per pound!
The Economic Advantage of Seed Oils
Health benefits and effects aside, seed oils are significantly cheaper than other cooking fats. While an 11-ounce jar of beef tallow costs $16, and a 17-ounce bottle of quality olive oil can run you upward of $10, you can get 17 ounces of organic canola starting at $7.
If you’re low-income or on a budget, it’s worth noting that using canola or another inexpensive seed oil can make cooking at home more accessible.
A Plant-Based, Low-Oil Approach
The evidence shows that the question of whether seed oils are healthy or dangerous is a complicated one, arriving with big doses of “compared to what” and “it depends.”
So what’s the bottom line here?
Remember that not all seed oils are the same — some have benefits, and others may be harmful.
For the most part, no matter what you cook at home, it will be better for your health than eating out at most restaurants, especially fast food, or bringing in processed dishes from the supermarket. And that’s especially true if you’re already struggling with a chronic disease or excessive weight.
Restaurant food and fast food tend to be high in trans fats, oxidized oils, excess sodium, high fructose corn syrup, processed carbs, and factory-farmed meat and dairy.
In addition to the source of the oil, how it’s processed and used in cooking will also make a big difference to its effects. A cold-pressed oil in your homemade salad dressing or drizzled on your kale is going to be much kinder to your body than oil that sits in a deep fryer for a week, turning out hundreds of batches of donuts or battered chicken.
And, as we’ve seen, whole foods like nuts, seeds, and avocados can provide fats in a more natural form. So getting your fat from seeds, instead of seed oils, is generally a healthier option, giving you fiber, vitamins, minerals, and other beneficial compounds.
Should You Avoid Seed Oils?
Completely avoiding seed oils is a personal choice, based on many of the pros and cons we’ve presented thus far. But if you’re looking for a to-do list to protect your health, here’s what I can leave you with:
- Avoid highly processed foods, regardless of the fat source.
- Avoid deep-fried foods (made with repeatedly heated cooking oil) found in restaurants and fast food.
- Prioritize whole plant foods over isolated fats like oils.
- Sauté with water or broth.
- If you choose to include oils in your diet, choose a non-GMO oil with low omega-6s or a favorable omega-6 to omega-3 ratio (such as flaxseed, olive, or avocado oil).
- And if you do use seed oils (especially the four commonly bioengineered ones — soy, corn, canola, and cottonseed), look for organic or non-GMO project-certified brands.
Less Is More When It Comes to Oil
While many seed oils are highly processed and found in unhealthy processed foods, they are not inherently harmful in all contexts. Some provide beneficial polyunsaturated fats, particularly when omega-6s are balanced with omega-3s. However, the refining process and excessive consumption of omega-6s in modern diets raise legitimate questions about their long-term health effects. And there’s nothing healthy about deep-fried foods, no matter what fat source they’re fried in.
Beef tallow and other animal-based fats promoted as a “natural” alternative have their own serious health and ethical concerns.
Ultimately, the healthiest approach may be minimizing added oils — whether from plants or animals — and focusing on whole food sources of fat like nuts, seeds, and avocados. Cooking with less oil is a simple, sustainable way to sidestep the debate while supporting long-term health.
Tell us in the comments:
- Do you cook with seed oils?
- Now that you’ve seen the pros and cons of seed oils, how do you feel about them?
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Featured Image: iStock.com/Jacob Wackerhausen
