6 Reasons Why Oil Is Bad for You (And Which Ones Are Worst)

Pretty much everyone accepts that processed food is bad for you—especially processed sugar. But most people are far less suspicious of processed fat—that is, oil. However, there are some diets, including a whole food plant-based diet, where oils are limited or avoided entirely.

In this post, I’ll be covering 6 different reasons why oil is bad for you. Most of them have to do with heart disease risk… but we’ll be touching on cancer, obesity, acne, inflammation, and more.

You’ll notice that some of the 6 reasons only apply to specific oils. So at the end of the post, I’ll also outline which oils are the healthiest, relatively speaking—in case you choose to keep consuming oil!

6 Reasons Why Oil Is Bad for You

I’ll be covering all these reasons in more depth below:

1. Excess omega-6 fat causes inflammation.
2. Saturated fat raises LDL cholesterol.
3. Oil raises blood triglyceride levels after meals.
4. Oil is high in calories.
5. Oil is low in micronutrients.
6. Most oils contain some amount of trans fat.

After we get through these 6 reasons, I’ll also cover which oils seem to be the healthiest, if you are going to consume oil.

If you prefer a video explaining these various points, this video covers many of the same points as my post:

Without further ado, let’s get into the 6 reasons why oil is bad for you!

1. Excess Omega-6 Fat Causes Inflammation.

One of the big reasons why the Western diet is thought to be so unhealthy today is the skewed balance between omega-3 and omega-6 polyunsaturated fatty acids. And the widespread use of vegetable oils are mainly to blame for this phenomenon.

Our body needs both omega-3 and omega-6 oils. But when present in higher quantities, omega-6 tends to be inflammatory, whereas omega-3 is anti-inflammatory.

Many of our common Western diseases involve chronic inflammation in the body—heart disease, cancer, arthritis, Alzheimer’s, inflammatory bowel disease, and more. And too much omega-6 could be part of what’s to blame. (source, source)

It’s believed that in our ancestral environments, our species likely ate close to a 1:1 balance of omega-6 and omega-3 fat. And it’s recommended to stay between that and a 4:1 balance (4 parts of omega-6 for each part of omega-3).

But today, our Western diet typically reaches a ratio between 10:1 and 50:1, skewed very heavily to the omega-6 fats (source).

This is because we eat so many processed vegetable oils that are high in omega-6.

Which Vegetable Oils Are Highest in Omega-6?

Here are the top offenders in this regard:

• Corn oil
• Soybean oil
• Sunflower oil
• Safflower oil
• Peanut oil
• Cottonseed Oil
• Sesame Oil

If you look at the quantity of omega-6 in just one tablespoon of these oils, you’ll see some numbers as high as 6 or 7 grams. (source, source)

When you compare that to olive oil, avocado oil, or canola oil, which are higher in monounsaturated fat, you only see 1 or 2 grams of omega-6.

Coconut oil and palm oil, which are primarily composed of saturated fat, contain only about 1 gram or less of omega-6 per tablespoon. (source)

Personally, I had heard about these problems with excess omega-6 years ago… But I only took action to cut out the high-omega-6 oils from my diet after I heard it could be what was causing my acne.

Yes—oils rich in omega-6 can cause acne. I wrote a lot more about this in my big post on how to clear acne as a vegan. If you struggle with acne, seriously go read that post. It took me years of studying and experimenting on myself to learn what I share in that post.

So anyway… whenever I see soybean oil, safflower oil, sunflower oil, or corn oil listed in a food, nowadays I steer clear. And I don’t cook with these oils at home anymore, either.

2. Saturated Fat Raises LDL Cholesterol.

If you’re avoiding omega-6 rich vegetable oils, you might consider switching to coconut oil or palm oil instead. Coconut oil is sometimes regarded as a health food for its medium-chain triglycerides (MCTs).

Honestly, it’s been a bit difficult for me to sort through fact and fiction when it comes to coconut oil… But I do have concerns.

Coconut oil and palm oil are high in saturated fat. They’re some of the only significant plant sources of saturated fat. Most other dietary sources of saturated fat are animal foods like fatty meat and cheese.

There’s a lot of controversy out there about saturated fat. But the main consensus is not good. Eating saturated fat can raise your LDL cholesterol (“bad cholesterol”), which is the biggest risk factor for heart disease. (source)

This is a big part of why vegan diets are known to be “heart healthy.” By cutting out animal products, you cut out most sources of saturated fat. So your LDL cholesterol drops, and your heart disease risk goes way down.

But does coconut oil raise LDL cholesterol, too? Yes. Apparently, it doesn’t clog your arteries quite as much as butter… But it still raises your LDL—so I definitely view it with some suspicion. (source)

3. Oil Raises Blood Triglyceride Levels After Meals.

Eating oil causes something called “After-Meal Fatty Blood” (or postprandial hyperlipidemia). After a meal of any oil, studies show elevated levels of fat (triglycerides) in the blood.

These elevated plasma triglyceride levels have been linked to atherosclerosis (clogged arteries), along with an inflammatory reaction and oxidative stress that could contribute to heart disease in the long-term (source).

This fatty blood is also more difficult for your heart to pump, and it’s been shown to coincide with chest pain (angina) in patients with heart disease.

This fatty blood is also slightly less oxygen-rich blood (by about 5-10%), making it less effective at doing its job of delivering oxygen to all your cells. (source)

This postprandial hyperlipidemia has been shown in studies with olive oil, canola oil, soybean oil, palm oil, saffola oil, and more. There’s no reason to believe that it is limited to only specific kinds of oil. It seems to be an effect of consuming the concentrated fat without any fiber attached to it.

My research for this section was highly aided by this resource by Mic the Vegan. In addition, here is a Harvard Heart letter that gives more general context on triglycerides and why they can be a problem.

4. Oil Is High in Calories.

Concentrated calories. It’s easy to over-eat on calories when you’re frying food or adding oil to recipes. It’s very calorically dense at 9 calories per gram, with no fiber to help fill you up or slow you down.

Oil gives you heaps of calories without filling much space in your stomach. So be aware of that if you’re trying to manage your weight.

Many vegan weight-loss programs recommend avoiding oils and even other high-fat foods for this reason. Instead of just eating one tablespoon of oil, you could have a whole apple and a half—or a lot of broccoli.

5. Oil Is Low in Micronutrients.

Some oils are worse than others in this regard, but remember: All oils are processed foods—the fiber and many of the other nutrients are often discarded, leaving just the fat, nothing more.

Extra virgin olive oil is known to contain a bit more as far as antioxidants in the final product. But if you look at the actual levels, they are still basically nothing compared to antioxidant-rich fruits or vegetables.

Whenever you eat food that’s low in micronutrients, you’re “crowding out” more nutrient-dense food from your diet. Sure, you can get away with eating a few low-nutrition foods each day… But most of your calories should come from foods that also give you lots of vitamins and minerals You don’t want too many empty calories!

6. Most Oils Contain Some Amount of Trans Fat.

All refined vegetable oils contain a small amount of trans fat, which is indeed the most harmful fat of all. This trans fat is created in the deodorizing process. (This does not apply to “cold-pressed,” “unrefined,” or “virgin” oils.)

If you look at a bottle of canola oil or vegetable oil, it will likely say “0 grams of trans fat”—but that’s a little misleading. As long as the total trans fat is less than 0.5 grams per serving, it can legally be listed as 0 grams. But if it’s a refined, bleached, deodorized oil, then it’s not truly 0 grams.

Canola oil has been shown to actually contain 1.9% to 3.6% trans fat content. Some of the omega-3 and omega-6 fats are converted to trans fat in the deodorizing process. Other refined oils are a bit lower, but not 0%. (source)

It’s been shown that any intake of trans fats raises your LDL cholesterol (and again, high LDL is the main heart disease risk factor). Trans fat also lowers your HDL (“good”) cholesterol (source).

So there is no intake of trans fat without some potential adverse effects. So in that sense, it would seem best to eat no refined oils.

But is this actually a major concern? Dr. Guy Crosby, writing for Harvard, believes it’s really not. He cites a study showing that canola oil, for instance, was part of a very successful heart disease reduction study.

One thing Dr. Michael Greger often points out is that trans fat is also naturally found in meat and dairy products. So if you really want to get to zero trans fat intake, you’d have to cut out animal products, too. And that would probably be the priority before eliminating the small amount in processed vegetable oils.

Partially Hydrogenated Oils: The Biggest Danger

It’s worth noting here that some oils have drastically higher trans fat levels, however. These are the partially hydrogenated oils. I wrote about these a bit in my post about vegetable shortening (Crisco).

Partially hydrogenated oils are now being banned in more and more parts of the world. So it’s likely they are no longer an issue where you live.

In 2015, the FDA declared partially hydrogenated oils to be no longer Generally Recognized as Safe (GRAS). By January of 2020, all food manufacturers were required to stop adding these oils to foods.

The World Health Organization has called to eliminate all uses of partially hydrogenated oils, globally, by 2023. If you look at products like Crisco today, they’ve switched to fully hydrogenated oils, which are free of trans fat.

But I find some of these articles about partially hydrogenated oils to be misleading. They sometimes say, as shorthand, “Trans fats are being banned.” But that’s not true.

Partially hydrogenated oils are what’s being banned. Other sources of trans fats—like meat and the small amounts found in other processed vegetable oil—are not being banned. If you want to avoid consuming those remaining sources of trans fat, it still takes your own diligence.

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Is All Oil Bad for You?

One final point I’ll share: Dr. Caldwell Esselstyn Jr. is one of the leading physician-scientists in the world when it comes to the prevention and reversal of heart disease… And he insists that his patients exclude oil from their diets.

In the video below, he concisely explains why, especially for those fighting heart disease, oil should not be on the menu—not even olive oil. He cites studies on:

• Impaired Artery Function. Vegetable oils have also been shown to impair the function of endothelial cells and flow-mediated dilation (FMD) in your arteries following a meal.

• Long-term Heart Disease Risk. There have been long-term studies showing that heart disease patients eating monounsaturated fat like olive oil had just as much disease progression as those eating saturated fat from animals.