Are vegetable and seed oils “toxic”?!
From TikTok to bestseller lists, vegetable oils—a.k.a. “seed oils”—are a big topic right now.
To be fair, folks have debated the merits of vegetable oils dating back to when they first entered the marketplace.
More recently, however, with the advent of the carnivore diet, vegetable oil hate has roared back into the socials. Maybe you’ve come across posts that refer to these cooking oils as “toxic sludge,” “motor oil,” “the hateful eight,” and “the biggest cause of chronic disease that nobody knows about.”
The anti-vegetable oil logic goes something like this…
Animal fats have been with humans for thousands of years. Vegetable fats, on the other hand, were invented during the last century when profit-seeking companies wanted to find a way to sell cheap-to-grow foods to unsuspecting consumers.
Another argument: Like margarine, vegetable oils were marketed as healthier alternatives for butter, and yet, people argue, these oils are worse than butter, raising your risk for obesity, anxiety, depression, ulcerative colitis, and more.
In contrast to the above line of thought, other experts will tell you that vegetable oils are harmless, potentially even health-promoting—and absolutely better than butter.
So, who’s right?
Like so many nutrition topics, the truth is too nuanced to fit on a meme.
In this story, we’ll help you sort the science from the pseudoscience so you can make informed decisions about the oils you choose to include in your diet.
What are vegetable oils?
Sometimes called “seed oils,” vegetable oils start, as you might suspect, from the seed of a plant. The most common ones you’ll find in a typical grocery aisle include:
- Canola oil
- Corn oil
- Safflower oil
- Sesame oil
- Sunflower oil
- Soybean oil
- Grapeseed oil
By the way, if you feel like there’s a bunch of oils missing from that list, it’s probably because those oils come from non-seed plants (such as olive, avocado, palm, or coconut oil, which all come from fruits, and aren’t considered vegetable or seed oils).
How are vegetable oils processed?
Non-vegetable oils—such as olive and avocado oil—are derived from naturally fatty foods. In fact, olives are so oily that you could theoretically make your own olive oil at home. (Just Google “how to make olive oil from scratch,” and you’ll find a number of videos walking you through the steps.)
The same can’t be said of most vegetable oils, which mostly come from foods with a relatively tiny fat content to begin with.
Case in point: A cup of green olives contains about 20 grams of fat,1 whereas a cup of corn has 2 grams.2
As a result, manufacturers must use an extensive multi-step process to extract this small amount of oil from these non-oily foods. These steps include:
- Crushing: A machine uses high pressure to press oil from the seeds.
- Refining: The seeds are heated with a solvent, such as hexane, to extract more oil.
- Deodorizing: To create a neutral taste and remove unwanted compounds, the extracted oil is then cooked at 400 F (204 C) for several hours.
During this process, health-promoting polyphenols and other stabilizing nutrients are lost, and small amounts of unsaturated fats are transformed into trans fatty acids (also called partially hydrogenated fat).
(Interesting fact: This also happens during deep frying. When vegetable oils sizzle in a restaurant’s deep fryer for hours, the trans fat content of the oil increases.)
To call these processed oils “toxic” might be an exaggeration. However, nutrition scientists generally agree that people should avoid trans fats in the diet, and in 2018, the Food and Drug Administration banned manufacturers from adding trans fats to processed foods.3 4
What cooking oils should you eat?
At PN, we’ve created several visual guides people can use to make informed decisions about what to eat.
(We’ve also created a shopping list, which you or your clients can print out and take to the grocery store. Check it out: Healthy Fats Shopping List)
In these guides, we’ve placed a few vegetable oils—expeller-pressed canola oil, high-oleic sunflower, and safflower oils—in the “Eat Some” section. For us, “eat some” is another way of saying that these foods will neither improve health nor harm health—when consumed in reasonable amounts. In some cases, like in the example of dark chocolate, when consumed in small amounts, they might even improve health.
The rest of the vegetable oils, along with butter and other saturated fats, fall into the “Eat Less” category, as the image below shows. You’ll find vegetable oils in bold.
We’ve gotten hate mail from folks who say certain vegetable oils—especially cold-pressed canola oil—should appear alongside olive oil in the “eat more” category. Plenty of others say all vegetable oils belong in the “eat less” column, and that butter belongs in “eat some” or even “eat more.”
To understand the scientific reasoning behind our recommendations, let’s explore some head-to-head matchups.
Extra-virgin olive oil vs. expeller-pressed canola oil
These oils are the least refined of their kind.
To make extra virgin olive oil (EVOO), manufacturers grind and mechanically press olives, without using any heat. Similarly, expeller-pressed canola oil is made by mechanically pressing rapeseed, without the use of heat or chemical solvents.
🟢 The case for extra virgin olive oil (EVOO)
Olive oil is richer in heart-healthy monounsaturated fatty acids (MUFAs) than almost any other cooking oil.
In addition, unlike the more refined “light” olive oil, EVOO maintains most of the olive fruit’s original polyphenols. These plant-based substances help to combat inflammation and protect cells from damage.
Perhaps most importantly…
More studies vouch for EVOO’s health-promoting qualities than for any other cooking fat.
For example, researchers asked 22,892 adults from Southern Italy to self-report their olive oil consumption. People who consumed the most olive oil (more than two tablespoons a day) were 20 percent less likely to die over the 13-year study than people who consumed the least olive oil (less than one tablespoon a day).5
Other research has linked the consumption of olive oil with a reduced risk of:
- High blood pressure6
- Heart disease
- Type 2 diabetes7
- Dementia8
- Cancer9
Consumption of olive oil is also associated with reductions in LDL cholesterol, especially when used to replace saturated fats like butter and coconut oil.10
Smoke point: Should you avoid cooking with olive oil?
Years ago, culinary experts recommended using EVOO only on salads and other uncooked foods. Back then, they assumed EVOO’s relatively low smoke point (350 to 410F) meant the oil would break down when heated, losing some of its distinctive flavor and health benefits.
We now know that smoke point isn’t as big a deal as previously thought.
That’s especially true in the case of EVOO, whose polyphenols and high concentrations of monounsaturated fats help keep the oil stable when heated.
In research that heated a variety of cooking oils to 464 F (240C) and then held them at 356 F (180C) for several hours, EVOO remained more stable than any other oil tested, including canola oil.11
🟡 The case for expeller-pressed canola oil
One of the more affordable cooking oils on the shelf, canola oil, is made from a Canadian-made hybrid of the rapeseed plant.
(The word “canola” refers to the first three letters of “Canada” with a fun “ola” added to the end for marketing purposes.)12
Among vegetable oils, canola is the richest in heart-healthy monounsaturated fats (though several non-vegetable oils have it beat) as well as alpha-linolenic acid, a plant-based omega-3 fatty acid.
In addition, canola oil contains plant substances called phytosterols that help influence blood cholesterol for the better, especially when used as a substitute for butter, research has found.13 14 15
The winner
Extra virgin olive oil is the clear winner.
The body of research in support of EVOO dwarfs the body of research in support of expeller-pressed canola.
In addition, EVOO has a more favorable fatty acid profile. By the way, so does avocado oil, which is why you’ll also find it in the “eat more” column.
However, you can buy roughly twice as much expeller-pressed canola oil for half as much money as EVOO. Because of this, expeller-pressed canola can be a good budget-friendly choice. In addition, because of expeller-pressed canola’s more neutral flavor, many people prefer it over EVOO for baking.
When used in moderation, expeller-pressed canola can be part of a healthy diet. It is likely to be at least health neutral, if not somewhat health beneficial.
Expeller-pressed canola oil vs. refined canola oil
This match-up comes down to how processing methods affect the end product.
🟡 Expeller-pressed canola oil
An expeller press is a machine that squeezes oil out of seeds.
It’s able to do this without the use of solvents or heat, which helps preserve beneficial compounds such as alpha-linolenic acid and phytosterols.
🔴 Refined canola oil
Refining removes some protective alpha-linoleic acid while adding small amounts of unhealthy trans fatty acids. This results in a product that is proportionally lower in omega-3 fatty acids and higher in omega-6 fatty acids.
The winner
Expeller-pressed canola oil wins, but only by a small margin.
That’s because canola oil starts with a less controversial fatty acid profile than many other vegetable oils, as the chart below shows. Soybean oil, for example, has less heart-healthy monounsaturated fat and much more theoretically inflammation-contributing omega-6 fat.
Are omega 6 fatty acids “inflammatory?”
The typical American consumes around 16 to 20 times more omega-6 fats than omega-3s.
This imbalance could theoretically increase inflammation in your body, potentially raising your risk for diabetes, obesity, and other health problems, argue some experts.16
Years ago, the recommendation to balance your omega 6s with omega 3s was widespread. (The suggested “ideal” ratio: Anywhere from 1:1 to 4:1, in favor of omega 6s.)
These days, there’s more debate among nutritional scientists as to whether this imbalance contributes to chronic inflammation, especially when those omega 6s are consumed in whole foods that contain many other beneficial compounds.
For example, nuts and seeds—both naturally rich in omega-6 fats—have been associated with a range of health benefits, including reductions in blood cholesterol and inflammation.17 18
In 2019, Harvard Health ran the headline “No need to avoid healthy omega-6 fats.” In support of their argument, a 2019 study from the American Heart Association journal Circulation determined that, if anything, the consumption of omega-6 fats reduced the risk for stroke, heart disease, and early death.19
However, while nuts and refined canola oil may share a somewhat similar fatty acid profile, the two foods differ in one important way. As we mentioned earlier, refined canola oil is basically pure oil. Meanwhile, nuts and seeds come packaged with health-protective fiber, polyphenols, protein, vitamins, and minerals.
Minimally-processed foods, like nuts or extra virgin oils, include a complex matrix of health-promoting nutrients. Highly-processed oils, on the other hand, have lost the vast majority of those healthful compounds, leaving mostly just the fatty acids which are more prone to oxidation (we’ll cover that next).
Refined vegetable oil oil vs. butter
This is the match-up that triggers the most arguing on the interwebs.
Let’s cover the major claims from both sides—plus what the research
