Corn oil, also called maize oil, is one of the most popular vegetable oils on the market. You’ll find corn oil in practically everything, from margarine to salad dressing to deep-fried foods in restaurants.
Corn oil contains high amounts of polyunsaturated fatty acids, which lower cholesterol[*] and are supposed to be a key part of heart health. But corn oil also causes inflammation and damages your liver. And like other vegetable oils, corn oil is actually linked to increased risk of obesity and heart disease[*].
What is Corn Oil?
Corn oil is one of the most popular cooking oils in the world.
It’s cheap, it’s flavorless, and it has a high smoke point, which makes corn oil a go-to choice for high heat frying, and particularly deep frying. Corn oil is 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 of corn oil[*]:
6 Reasons to Avoid Corn Oil
#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 throw out saturated fats like butter, coconut oil, and palm oil and replace them with vegetable oils[*].
This recommendation is based on bad science. 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, like corn oil — are especially damaging to your heart.
#2: Corn Oil 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, eventually blocking your arteries and causing 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 corn oil. Even unheated linoleic acid has major drawbacks.
#3: Corn Oil 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 of 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. It’s not great for your cholesterol either, despite what manufacturers claim.
#4: Corn Oil is Bad For Your Arteries
Vegetable oil producers (and the American Heart Association) maintain that corn oil is heart healthy because it lowers both LDL and total cholesterol levels[*].
It’s true that corn oil decreases cholesterol. However, LDL cholesterol (LDL-C) and total cholesterol (TC) are both poor predictors of heart disease risk.
There actually 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 actually 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:
- People with high levels of phytosterols get very bad 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 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 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 cause type 2 diabetes — and high fat keto diets reverse it[*].
But those fats must be healthy fats, because — in addition to its obesogenic effects — linoleic acid contributes to insulin resistance, the precursor to diabetes [*].
So corn oil is a bad choice for your metabolism, insulin function, and diabetes risk. It’s also a bad choice for your liver.
#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 and harder for your liver to work properly. Sadly, 30-40% of Americans now have NAFLD[*], and vegetable oils rich in omega-6 fatty acids are 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.
How to Choose Healthy Fats
The good news is that you have plenty of healthy fat options to replace corn oil. Here’s how you can avoid corn oil and eat the best fats possible instead:
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 the label is free of corn oil, soybean oil, etc.
Cook With MUFA And SFA
If there’s one thing you 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 and SFAs. 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.
Stay Away From Corn Oil
You’ve likely heard that corn oil and other vegetable oils are great for your heart and will contribute to a long, healthy life.
The opposite is true.
Avoid corn and vegetable oils as often as you can. Choose healthy, monounsaturated and saturated fats instead, and eat plenty of them. You’ll feel the difference in your body and brain.