Many people think vegetable oils are healthy. After all, the American Heart Association has endorsed soybean oil, corn oil, and the rest of the vegetable oils as “heart-healthy” for decades[*]. But is vegetable oil bad for you?
Certain vegetable oils have made their way into more and more food (especially processed foods) over the last 50 years, while fats like butter and coconut oil have been phased out.
But don’t be fooled: 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. These oils are harmful to your metabolism, inflammation levels, oxidative stress, weight regulation, and risk of cancer.
This article will cover the science behind vegetable oils, the top vegetable oils to avoid, and what to use instead of these oils.
For the last half-century, the American Heart Association has maintained that saturated fat drives heart disease. The organization suggests replacing saturated fats like butter and coconut oil with “heart-healthy” vegetable oils rich in omega-6 fatty acids.
However, more research is coming out that suggests the exact opposite is true. In the last decade, several extensive, independent reviews of the research have found that dietary saturated fat is not associated with cardiovascular risk factors, including heart attacks[*][*].
When you 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.
The four major types of fatty acids are:
- Saturated fatty acid (SFA)
- Monounsaturated fatty acid (MUFA)
- Polyunsaturated fatty acid (PUFA)
- Trans fatty acid (trans fat)
You already learned about saturated fatty acid. SFA is satiating, resists oxidation, and is stable at high heats, which makes it great for cooking. Contrary to popular wisdom, SFAs are healthy and do not raise cholesterol levels.
Next come MUFAs. High MUFA intake correlates with several health benefits, including lower blood pressure, lower blood glucose, and reduced 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 those in vegetable oil.
Finally, there are artificial trans fats — or hydrogenated PUFAs. Artificial trans fats are by far the worst type of fat around. Fortunately, researchers have shown how bad they are, and at this point, trans fats are illegal in most parts of the world[*].
Omega-6 PUFAs aren’t as harmful as trans fats, but they aren’t great for you either.
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 May Stunt Weight Loss
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 strong predictor of obesity[*]. If you want weight loss, 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 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.
The bottom line is that vegetable oils rich in linoleic acid are not good for cooking.
When you’re ready to remove vegetable oils from your diet, start by getting rid of these common products from your cupboards.
1. Soybean Oil
Soybean oil is the most consumed vegetable oil in America, mainly because it’s exceptionally cheap[*]. You’ll find soybean oil on the ingredient lists of salad dressings, spreads, junk food, baked goods, 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, 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.
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[*].
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.
Is vegetable oil bad for you? The answer is clear. Here’s a list of healthy cooking oils and good fats (both plant-based and animal fats) that you can use for eating or cooking:
- Coconut oil
- MCT oil
- Avocado oil
- Extra virgin olive oil
- Cream cheese
- Responsibly sourced, 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.
So, Is Vegetable Oil Bad for You?
The answer is yes.
Vegetable oils are hard to avoid. Major influencers — the AHA included — are committed to a decades-old narrative: that healthy oils come from polyunsaturated fat, while saturated fat is bad for you.
But recent research disagrees. There’s a lot of evidence that shows you’re better off avoiding vegetable oils and the omega-6 fats within them. Studies show that vegetable oils can lead to obesity, cause inflammation, and increase the presence of free radicals in the body.
Here’s a better choice: Stick to healthy fats instead. If you want to know what to eat, check out this complete list of anti-inflammatory, nutrient-rich, high-fat foods that are perfect for a keto diet.