Cooking fats used to be simple: butter, lard, tallow, and olive oil—natural, nourishing staples of human diets for centuries. But in the last hundred years, a sneaky newcomer has taken over our plates: vegetable and seed oils.
Today, they’re nearly unavoidable. Seed oils lurk in foods most people swear they don’t eat—chips, cereal, chocolate—and in “healthy” foods like salad dressings, spice blends, nut milk, and even baby formula. They’re in restaurant meals and snack packs alike. If I had to guess, seed oils are in about 90% of the packaged foods at your local store.
Why? They’re cheap, have a long shelf life (if stored properly), and unfortunately, so does the damage they cause. Think of seed oils as the sketchy used car salesmen of the food world. They flash a big “heart-healthy” badge, but once you dig into the details, problems like oxidative stress, inflammation, and harmful byproducts spill out.
What are Seed Oils?
Seed oils are extracted from seeds like sunflower, safflower, canola (rapeseed),
corn, and soybeans. In contrast, vegetable oils can be extracted from seeds, leaves, or fruits, often blended and marketed under vague names like “vegetable oil.”
Unlike olive or coconut oil, which are extracted by pressing, seed and vegetable oils require industrial processing.
Here’s how it typically works:
- Chemical Solvents: Hexane is used to extract the oil from the seeds.
- High Heat: The oils are heated to extreme temperatures, breaking down nutrients.
- Refining: The oils are bleached and deodorized to make the dirty gunk look and taste appealing.
The Nerdy Stuff: Fats, Bonds, and Stability
Saturated fats—like lard, tallow, cream, butter, and coconut oil—are structurally
stable because they’re “saturated” with hydrogen atoms. Every available bond is filled, making them solid at room temperature and able to handle high heat without breaking down, which is why they’ve traditionally been used for cooking.
Unsaturated fats—like those in avocados, fish, olives, and nuts—contain one or
more double bonds in their molecular structure. These double bonds create “kinks” in the fatty acid chains, making them more flexible but also more prone to oxidation (going rancid) when exposed to heat, light, or air.
By the time these oils hit your shelves, they’re far from the nutrient-rich fats our
ancestors consumed.
Unsaturated fats are divided into:
- Monounsaturated fats (MUFA): Contain one double bond (e.g., olive oil, avocado oil, nuts). These fats are more stable than polyunsaturated fats and are associated with heart health benefits.
- Polyunsaturated fats (PUFA): Contain two or more double bonds (e.g.,soybean oil, sunflower oil, fish, corn oil). These are less stable due to multiple double bonds, making them particularly vulnerable to oxidation. Polyunsaturated fats are further classified by the position of the first double bond:
- Omega-3 fatty acids: The first double bond is on the third carbon (e.g., fattyfish, flaxseeds). These fats are anti-inflammatory and essential for brain and heart health.
- Omega-6 fatty acids: The first double bond is on the sixth carbon (e.g.,soybean oil, sunflower oil). While essential in small amounts, excess omega-6 can promote inflammation when not balanced with omega-3 intake.
The more double bonds a fat has, the more unstable it becomes, which is why
polyunsaturated fats are particularly delicate and prone to damage during cooking or processing and why Japanese eat fish raw.
The Omega Imbalance
Seed oils, like those from soybean, sunflower, and corn, are rich in omega-6 fatty acids, especially linoleic acid. Until about 100 years ago, humans consumed minimal amounts of this type of fat. But with the rise of industrial seed oils, omega-6 intake has skyrocketed.
While your body needs both saturated and unsaturated fats to function, an
overwhelming intake of omega-6 fatty acids—primarily from seed oils—can throw off your natural fat balance. This imbalance is particularly problematic when omega-6 significantly outweighs omega-3, as it has been linked to increased inflammation, obesity, and heart disease.
Interestingly, omega-6 is naturally found in foods like eggs, avocados, and meat, which also provide omega-3s in smaller amounts. These whole foods offer a more balanced and healthful ratio of fats compared to the concentrated, excessive amounts of omega-6 found in processed seed oils. I’d much prefer you to get your fats from these nutrient-dense sources rather than from oils that can exacerbate an already common imbalance in modern diets.
Understanding these structural differences can help you make more informed choices about the fats you include in your diet—and which ones you might want to avoid.
Restaurants and Seed Oils
It’s not just packaged foods. Eating out without encountering seed oils is a mighty feat. Restaurants use them for the same reasons manufacturers do: they’re cheap, convenient, and long-lasting. And while I’d love to believe it’s all an innocent oversight, for most businesses, the bottom line is the dollar. Restaurants don’t set out to harm you with seed oils, but they also aren’t going to willingly spend 4–10 times more on alternatives that don’t boost their profits.
The Rise of Seed Oils
How did oils like canola, soybean, and sunflower go from industrial waste to kitchen staples? It’s a story of clever marketing. Originally, these oils were industrial byproducts—cheap and easy to repurpose. Manufacturers realized they could process them for human consumption and sell them as “better” than traditional fats like butter or lard.
Does this remind anyone of the sugar industry decades ago? Back then, the highest bidder shaped public perception, and today, seed oils benefit from a similar narrative.
We’ve been sold on the idea of “heart health” while the real science tells a more troubling story. Remember the “I can’t believe it’s not butter!” craze? I do. It’s one of my strongest childhood memories. That line was the centrepiece of family conversations for years.
My uncle—who, I swear, was John Candy’s twin—would repeat it endlessly, cracking us all up. And now, here I am, thinking, “I can’t believe we all fell for that.”
How did oils like canola, soybean, and sunflower go from industrial waste to kitchen staples? It’s a story of clever marketing. Originally, these oils were industrial byproducts—cheap and easy to repurpose. Manufacturers realized they could process them for human consumption and sell them as “better” than traditional fats like butter or lard.
Does this remind anyone of the sugar industry decades ago? Back then, the highest bidder shaped public perception, and today, seed oils benefit from a similar narrative.
We’ve been sold on the idea of “heart health” while the real science tells a more troubling story. Remember the “I can’t believe it’s not butter!” craze? I do. It’s one of my strongest childhood memories. That line was the centrepiece of family conversations for years.
My uncle—who, I swear, was John Candy’s twin—would repeat it endlessly, cracking us all up. And now, here I am, thinking, “I can’t believe we all fell for that.”
Fats and Oils to Love or Loathe:
Fats and Oils We Love
- Tallow, Dripping and Lard: Traditional, flavourful, and great for high-heatcooking. They are all made from nothing but animal fats which is what wewant!
- Butter and Ghee: Stable, delicious, and real food. Stay tuned for a butter vs. ghee showdown in an upcoming recipe on how to make both!
- Extra Virgin Olive Oil: This is the highest-quality olive oil, made from the first cold pressing of olives without heat or chemicals. It’s best used raw (e.g., in salads or drizzled over dishes) because heat can break down its delicate flavour and nutrients.
- Coconut Oil: Stable, but make sure you buy the kind that solidifies at roomtemperature—liquid versions have been refined.
- Virgin Olive Oil: A slightly lower grade than EVOO, also obtained throughmechanical pressing but with a slightly higher acidity level. Like EVOO, it’s better suited for raw or low-heat applications.
- Seed Oils: Canola (rapeseed) oil, soybean oil, sunflower oil, safflower oil,corn oil, grapeseed oil, cottonseed oil, and rice bran oil.
- Veg Oils: (often blends or processed): Vegetable oil (generic label),margarine, hydrogenated oils.
- Shortening: a solid fat made from vegetable oils – not my thing!
- Pure or Regular Olive Oil: A blend of refined olive oil (processed with heatand chemicals) and virgin oil.
- Pomace Olive Oil: Made from the leftover olive pulp after pressing. It’s chemically extracted and refined.
A Quick Note on Avocado Oil 🥑
While writing this, I had a “wait a second” moment about avocado oil. It’s marketed for its high smoke point, but as an unsaturated fat, it should technically be less stable when heated. Something doesn’t add up, and I’ll need to dig deeper. Until then, I’d suggest treating it like extra virgin olive oil—best used raw or for low-heat cooking.
While writing this, I had a “wait a second” moment about avocado oil. It’s marketed for its high smoke point, but as an unsaturated fat, it should technically be less stable when heated. Something doesn’t add up, and I’ll need to dig deeper. Until then, I’d suggest treating it like extra virgin olive oil—best used raw or for low-heat cooking.
Adding to this, both olive oil and avocado oil have troubling reputations for being adulterated. Studies have found up to 89% of samples don’t contain what they claim. Many are cut with cheaper oils like canola. One investigation revealed 83% of avocado oil products tested were mostly or entirely canola oil, falsely labelled as pure avocado oil.
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