Many people think vegetable oils are healthy. The word vegetable might have something to do with it. Or maybe it’s the American Heart Association — a group that’s endorsed soybean oil, corn oil, and the rest of the vegetable oils as “heart healthy” for nearly half a century[*].
Whatever the reason, what’s certain is that vegetable oils have made their way into more and more foods (especially processed foods) over the last 50 years, while fats like butter and coconut oil have been phased out.
Vegetable oils have no place on a healthy ketogenic diet. The trouble is that vegetable oils are rich in linoleic acid and other inflammatory and easily oxidized omega-6 fatty acids.
Vegetable oils are bad for your metabolism, inflammation levels, oxidative stress, weight regulation, and cancer risk.
Vegetable Oils, Saturated Fat, and Heart Disease
For the last half-century, the American Heart Association has maintained that saturated fat is a driving cause of heart disease and that for the sake of your heart, you should replace saturated fats like butter and coconut oil with “heart healthy” vegetable oils rich in omega-6 fatty acids.
However, more and more research is coming out that suggests the exact opposite. In the last decade, several large, independent reviews of the research have found that dietary saturated fat is not associated with heart disease[*][*].
And foods high in saturated fat — eggs, palm oil, and coconut oil — are rich in beneficial nutrients like choline, carotenoids, and medium chain triglycerides (MCTs).
When you store (or eat) fat, you store it in triglyceride form. When it’s time to use that fat for energy — on a ketogenic diet, for instance — the triglyceride is broken down into fatty acids.
Fatty acids are the building blocks of fat. There are a few different types, each with unique effects on your health.
Here are the four major types of fatty acids:
- Saturated fatty acid (SFA)
- Monounsaturated fatty acid (MUFA)
- Polyunsaturated fatty acid (PUFA)
- Trans Fatty Acid (trans fat)
You already learned about SFA. SFAs are satiating, resists oxidation, and is stable at high heats, which makes it great for cooking. Contrary to popular wisdom, SFA is healthy.
Next come MUFAs. High MUFA intake correlates with lower blood pressure, lower blood glucose, and lower cardiovascular risk[*].
You won’t find many folks bashing monounsaturated fats. They’re the main type of fat in olive oil and avocado oil, and are prevalent in the Mediterranean Diet, which is one of the best-studied diets for longevity.
Then there are PUFAs. PUFAs can be divided into anti-inflammatory omega-3 fatty acids like the ones you find in fish, and pro-inflammatory omega-6 fatty acids like the ones you find in vegetable oil.
Finally, artificial trans fats — or hydrogenated PUFAs. Artificial trans fats are by far the worst type of fat around. Luckily, researchers have shown how bad they are, and at this point, trans fats are illegal in most parts of the world[*].
The Problems With Linoleic Acid
Most vegetable oils contain a particularly damaging omega-6 PUFA called linoleic acid. Linoleic acid is bad for you in a few different ways.
1) Linoleic Acid Causes Obesity
Historically, humans have eaten close to a 1:1 ratio of omega-6 to omega-3 fats. Researchers believe that this ratio is optimal for human health[*].
But in America, largely thanks to vegetable oils, the O6:O3 ratio is now closer to 20:1 — far in favor of omega-6s, mostly linoleic acid.
That skewed ratio is a very good predictor of obesity[*]. If you’re looking for weight loss, you’ll want to avoid linoleic acid and other omega-6 PUFAs.
Excess linoleic acid turns into another omega-6 PUFA called arachidonic acid, which triggers inflammation pathways and downregulates metabolism, which causes rapid weight gain [*].
2) Linoleic Acid Causes Inflammation
Another consequence of excess linoleic acid is inflammation. Linoleic acid turns into pro-inflammatory compounds called eicosanoids that cause an immune response in your cells, creating low-level inflammation[*].
3) Linoleic Acid Oxidizes When Cooked
For heart health, the AHA endorses high-linoleic oils for cooking[*]. The problem is that linoleic acid in corn oil, soybean oil, and other vegetable oils is highly unstable. When it’s exposed to high temperatures, it oxidizes.
The combination of high heat and unstable fat generates particles called oxidized lipids[*]. There are two ways oxidized lipids accelerate the progression of heart disease:
- Inflammation: Once ingested, oxidized lipids interact with free radicals — reactive oxygen species (ROS) — in your bloodstream. This interaction triggers your immune system, creating inflammatory conditions in which atherosclerotic (heart disease) plaques develop.
- Oxidized LDL: Low density lipoprotein (LDL) particles transport lipids through your bloodstream for energy. So if you eat oxidized lipids, LDL particles pick them up — causing the LDL itself to oxidize. Oxidized LDLs then penetrate the arterial wall, creating inflammation that results in clogged arteries that increase your risk of heart disease.
Top 7 Vegetable Oils to Avoid
#1: Soybean Oil
Soybean oil is the most consumed vegetable oil in America, largely because it’s exceptionally cheap to manufacture[*].
You’ll find soybean oil on the ingredient lists of salad dressings, spreads, junk food, baked good, fries, and so on. Most soybean oil comes from GMO soybeans.
Soybean is about 55% linoleic acid, which contributes to weight gain, inflammation, and all the other problems you read about above. It’s also ultra-purified, which leaves it devoid of any meaningful nutritional value. You’re better off avoiding it.
#2: Peanut Oil
Peanut oil is popular for frying foods. It lends a flaky texture and nutty flavor during the deep-frying process.
But again, peanut oil is rich in linoleic acid, and eating it increases your risk of heart disease, diabetes, liver disease, and even cancer[*].
Peanut oil has a fair amount of vitamin E, which companies have used to say that it’s healthy. But the cons outweigh the pros here. You’re better off getting your vitamin E from olive oil and avocados instead.
#3: Corn Oil
Corn oil is especially high in phytosterols, the plant version of cholesterol. One of the selling points of corn oil is that it lowers cholesterol; that happens because phytosterols block cholesterol absorption in the gut[*], which lowers total cholesterol and LDL levels.
But phytosterols have a lot of problems:
- Higher phytosterol levels correlate with increased heart disease risk in postmenopausal women[*]
- Elevated sitosterol — the most common phytosterol in vegetable oils — correlates with major coronary events in high-risk men[*]
- Large population data links serum phytosterol levels to cardiovascular disease risk[*]
- Sitosterolemia — 50-100x normal phytosterol levels — may cause heart disease at a young age[*]
Increased phytosterol levels are linked to increased heart disease risk[*]. And on top of that, corn oil contains 57% linoleic acid, which makes it one of the worst cooking oils available.
#4 Canola Oil
As far as vegetable oils go, canola oil isn’t the worst offender. Here’s the fatty acid profile of canola oil [*]:
- SFA: 7.4%
- MUFA: 63.3%
- PUFA: 28.1%
- Trans fat: 0.4%
For cooking or eating, 28.1% is still too much PUFA. Nonetheless, canola oil has far less linoleic acid than soybean oil or corn oil.
The FDA has endorsed canola oil for heart disease risk reduction[*]. This is probably because canola oil is high in MUFA and reduces cholesterol.
But like corn oil, canola oil reduces cholesterol via phytosterols — those nasty molecules that seem to increase heart disease risk.
Canola oil also contains erucic acid, which impairs heart function, liver function, and fat metabolism in animal studies[*][*]. Canola oil is required to have less than 2% erucic acid[*], but 2% isn’t nothing. You’re still better off avoiding it.
#5 Cottonseed Oil
Cotton doesn’t seem like a vegetable, but cottonseed oil — extracted from the seed of the cotton plant — is nonetheless considered a vegetable oil.
Cottonseed oil was the original oil in Crisco and is a favorite of many restaurants for high-heat cooking because it’s flavorless [*].
But since cottonseed oil is around 55% linoleic acid, restaurants that use it are serving up heaping portions of oxidized lipids. Not good for your heart.
#6 Sunflower Oil
The National Sunflower Association refers to sunflower oil as “your healthy choice”[*]. It’s ironic because sunflower oil is one of the worst offenders when it comes to vegetable oil — it clocks in at more than 60% linoleic acid.
On top of that, a study that fed rats either sunflower oil-rich feed or olive oil-rich feed found that the sunflower oil group had significant DNA damage, which speeds up aging and increases the risk of disease and cancer[*].
You’re best off avoiding sunflower oil.
#7 Safflower Oil
Safflower oil is the worst vegetable oil you can use. It has up to 70% linoleic acid[*], which comes with all the problems you’ve already read about. It’s unstable for high-heat cooking, it’s devoid of nutrients, and it increases inflammation and heart disease risk.
Healthy Fats For Eating And Cooking
Here’s a list of healthy cooking oils and good fats that you can use for eating or cooking:
- Coconut oil
- MCT oil
- Avocado oil
- Olive oil
- Cream cheese
- Red palm oil
- Heavy cream
Red palm oil, ghee, and avocado oil — due to high smoke points and oxidative stability — are best for cooking. They’re also a good source of nutrients.
The Verdict On Vegetable Oil
Vegetable oils are hard to avoid. These oils are advertised as healthy. Major influencers — the AHA included — are committed to a decades-old narrative: that polyunsaturated fat is good for you, while saturated fat is not.
But recent research disagrees. There’s a lot of evidence that you’re better off avoiding vegetable oils and the omega-6 fats within them.
Stick to healthy fats instead. If you want to know exactly what to eat, check out this complete list of anti-inflammatory, nutrient-rich, high-fat foods that are perfect for a ketogenic diet.