Corn oil, also called maize oil, is one of the most popular vegetable oils on the market. You’ll find it in practically everything, from margarine to salad dressing to deep-fried foods in restaurants.
Corn oil contains high amounts of polyunsaturated fatty acids (PUFAs), which lower cholesterol[*] and are supposed to be a key part of heart health. But this oil can also cause inflammation and damage your liver. And like other vegetable oils, it’s linked to increased risk of obesity and heart disease[*].
This article will cover the health effects of corn oil, and why you’re better off swapping it out for a healthier fat source.
Corn oil is one of the most popular cooking oils in the world.
It’s cheap, flavorless, and has a high smoke point, which makes it a go-to choice for high-heat frying, particularly deep frying. It’s also in margarine, salad dressings, beauty products, and more.
Corn oil is a vegetable oil, and like all vegetable oils, it’s high in polyunsaturated fat. Here’s the fatty acid composition[*]:
Corn oil is rich in PUFAs, and particularly the omega-6 PUFA linoleic acid. That’s supposed to make it good for your heart. But there are a few reasons you don’t want omega-6s in your diet.
#1: Vegetable Oils Are High In Inflammatory Fats
According to the American Heart Association (AHA), the fatty acid profile (low SFA, high PUFA) of corn oil is heart healthy. Because of this, the AHA recommends you replace saturated fats like butter, coconut oil, and palm oil with vegetable oils[*].
This recommendation is based on outdated information. It started with observational data collected in the 1950s that linked dietary saturated fat to heart disease[*].
Yet saturated fat remains taboo, and vegetable oils have taken their place in the standard American diet.
This dynamic is backward because vegetable oils — especially ones high in linoleic acid — are especially damaging to your heart.
#2: It Isn’t Heat Stable
Corn oil is rich in linoleic acid, a polyunsaturated fatty acid common in vegetable oils.
Linoleic acid is polyunsaturated because the fat molecule is missing multiple hydrogen bonds. The more missing bonds a fat molecule has, the more sites are open for a free radical to come in and oxidize the fat, breaking its integrity and making it inflammatory.
Oxidation happens more at high temperatures, which is why it’s best to cook with saturated fats (which have no openings; they’re saturated).
Polyunsaturated fats are the most fragile, and the worst for cooking. With just a little bit of heat, PUFAs start to oxidize.
Oxidized fats get into your bloodstream and form plaques in your arteries. In other words, they promote heart disease[*].
More specifically, oxidized fats increase the amount of oxidative stress and inflammation in your arteries. These conditions make it easy for an LDL cholesterol particle to come along and penetrate the artery wall.
The cholesterol particles build up in response to inflammation, which can eventually block your arteries and lead to heart disease.
That’s why you don’t want to cook with corn oil. Despite being labeled “heart healthy,” it’s actually one of the worst things you can do for your heart.
And it’s not just cooking with this oil that’s problematic. Even unheated linoleic acid has major drawbacks.
#3: It May Contribute to Obesity
Cooking with corn oil is no good. Oxidized lipids are among the worst substances you can eat. But what about unheated corn oil in your salad dressing?
Don’t you need some omega-6s like linoleic acid? Isn’t that good for you?
Yes and no. You do need both omega-6 fatty acids (O6) and omega-3 fatty acids (O3), but the key is to balance the two. Research says the ideal ratio is O6:O3 is 1:1[*].
The problem is that most Americans eat about 20:1 O6:O3. Most of that O6 is linoleic acid — the primary fat in corn oil, soybean oil, canola oil, safflower oil, and other vegetable oils.
New research suggests that the unbalanced O6:O3 ratio is one of the main drivers of obesity in the United States[*], particularly when most of that O6 is linoleic acid (like in corn oil).
Linoleic acid is a precursor to arachidonic acid (AA) — and AA causes weight gain by activating the endocannabinoid system[*].
And with that obesity comes a rise in heart disease risk[*]. Obesity ties closely to insulin resistance, high blood sugar, diabetes, dyslipidemia, high blood pressure, and a host of other CVD risk factors.
Corn oil and other high-linoleic vegetable oils contribute to inflammation and drive weight gain and heart disease.
#4: It’s Bad for Your Arteries
Vegetable oil producers (and the American Heart Association) maintain that corn oil is heart-healthy because it can lower both LDL and total cholesterol levels[*].
However, LDL cholesterol (LDL-C) and total cholesterol (TC) are both poor predictors of heart disease risk.
There isn’t much of a link between either one and heart disease. The far better predictor is LDL particle number, or LDL-P [*]. No research shows that corn oil affects LDL-P.
The other issue is the mechanism through which corn oil lowers cholesterol: phytosterols. Phytosterols are the plant version of cholesterol, and humans don’t process them particularly well.
By weight, corn oil is about 0.77% phytosterol. That may not sound like much, but it’s a lot because phytosterols are potent. Just a few hundred milligrams can significantly lower cholesterol levels[*].
Phytosterols work by blocking cholesterol absorption in your gut — the more phytosterols you eat, the less cholesterol can get into your bloodstream [*].
You might think that’s good for your heart, but the data suggests the opposite is true:
- People with high levels of phytosterols are at risk for heart disease at a very young age[*]
- Postmenopausal women with high serum phytosterols have a significantly higher risk for coronary artery disease[*]
- Elevated phytosterol levels link tightly to heart attacks in high-risk men[*]
- Data from the Framingham study, the largest and longest-running heart disease study in history, suggests that higher serum phytosterols may increase CVD (cardiovascular disease) risk[*]
To be clear, this data doesn’t fully resolve the issue. These studies have all the same problems that the original research on cholesterol and heart disease had — they’re correlational and not well controlled.
However, they paint a fairly clear picture: Plant sterols may lower cholesterol, but they’re possibly more damaging to your heart than cholesterol itself.
#5: Corn Oil and Diabetes
The linoleic acid in corn oil drives obesity, and with that weight gain comes increased risk of Type 2 diabetes.
Type 2 diabetes is a component of metabolic syndrome — a disease characterized by insulin resistance, high blood sugar, high insulin, and obesity. High-carb, high-sugar diets are strongly linked to Type 2 diabetes — and high-fat keto diets may reverse it[*].
But those fats must be healthy fats, because — in addition to its obesogenic effects — linoleic acid contributes to insulin resistance, which is the precursor to diabetes[*].
#6: Corn Oil and Liver Disease
Another epidemic sweeping across the United States is non-alcoholic fatty liver disease or NAFLD.
NAFLD is when fat builds in your liver, making it harder for your liver to work properly. Sadly, 30-40% of Americans have NAFLD[*], and vegetable oils rich in omega-6 fatty acids are thought to be one of the main contributors[*].
Supplementing with omega 3s may mitigate liver damage by balancing out the O6:O3 ratio[*], but your best bet is to avoid vegetable oils to keep your liver from having to process all those omega-6s in the first place.
The good news is that you have plenty of healthy fat options to replace corn oil. Here’s how you can make healthier choices:
Corn oil is cheap and widely available, so a lot of packaged food companies use it whenever they can. When you buy something at the store, make sure you read the label to avoid this ingredient.
Cook With MUFA and SFA
If there’s one thing to take away from this article, it should be this: Never cook with high-PUFA vegetable oils.
Instead, use heat-stable cooking oils that are rich in MUFAs (monounsaturated fatty acids) and SFAs (saturated fatty acids). Butter, avocado oil, red palm oil, lard, and tallow are all good high-heat cooking options. You’ll avoid those oxidized lipids, and your heart will thank you.
Make High-Fat Healthy Fat
If you’re on a high-fat diet like a ketogenic diet, you want to make sure you’re getting the best fats possible. Vegetable oils do not qualify.
Use Caution With Extra Virgin Olive Oil
While extra virgin olive oil has numerous health benefits[*], it’s not an oil that you should be frying with.
Extra virgin olive oil is fine for drizzling on cooked foods, salads, or dips. However, because of its low smoke point, it’s best not to use it for frying. It can be safely used for sautéing, but beyond 375°F degrees its fatty acids begin to oxidize and loses a lot of its health benefits.
You’ve likely heard that corn oil and other vegetable oils are great for your heart and will contribute to a long, healthy life. But this information is outdated.
Avoid these oils as often as you can. Choose healthy, monounsaturated and saturated fats instead, and eat plenty of them. When you do eat less stable fats, make sure they’re in the form of healthy omega-3 fatty acids. Your body and brain will thank you.
For an easy way to boost your healthy fats, try this MCT Oil Powder that adds seven grams of easy-to-process to your daily intake.