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:

Mic the Vegan explains how oil may be responsible for heart disease and type-2 diabetes still experienced by some vegans despite cutting out animal fats.

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)

Dr. Michael Greger explains the evidence showing that coconut oil raises LDL cholesterol and heart disease risk.

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.

Red blood cells. Photo: Naz Amann.

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.

Baked goods like croissants, made with vegetable shortening, have long been seen as sources 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.

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.

Dr. Caldwell Esselstyn, author of Prevent and Reverse Heart Disease (Amazon link), explains why he recommends heart disease patients strictly consume no oil.

Is Oil Vegan?

Oil is generally considered vegan. Most oils do not contain animal products. However, vegans eating a whole-food plant-based diet may choose to limit or completely avoid some or all oils for health reasons.

Which Oils Are Healthiest?

So, there are reasons to be concerned about eating too much of any processed oil. That said, there are still better oils, relatively speaking.

In Dr. Michael Greger’s book How Not to Die (Amazon link), he uses a traffic light analogy to rank foods as healthy or unhealthy:

  • Green-light foods should be eaten in any quantity.
  • Yellow-light foods should be limited.
  • Red-light foods should ideally be avoided.

Where does he rank the various oils on this scale? He ranks all vegetable oils as red-light foods except for extra-virgin olive oil, which he ranks as a yellow-light food.

Let’s take a look at some of the potentially healthier oils and why they’re thought to be less harmful.

Extra Virgin Olive Oil (EVOO)

EVOO is one of the oils that is also championed by the paleo and keto folks. (Sometimes I like to cross-compare to see what the vegan gurus and the paleo gurus actually agree on—because they disagree about so much!)

EVOO is high in monounsaturated fat (one of the healthier kinds), and it contains some antioxidants like vitamin E, as well.

That said, olive oil is still shown to increase triglycerides in the blood and impair endothelial function for a time after eating it. And it’s still easy to over-eat on calories. So, olive oil not a full-on health food.

Avocado Oil

Avocado oil is another one of the oils rich in monounsaturated fat—it has a similar fat profile as olive oil. And it’s another oil that is celebrated by paleo folks.

I haven’t heard any vegan nutrition gurus address avocado oil specifically. My guess is that it would fit into that “yellow-light” category of foods along with olive oil. It contains mostly healthy kinds of fat, but it’s still processed—so it’s less healthy than whole avocados.

Omega-3 Rich Oils: Flax Oil, Walnut Oil, Canola Oil?

I haven’t mentioned these oils up to this point because they’re used in very different ways. None of these omega-3 rich oils are commonly used as cooking oils.

Because of their low smoke points, flaxseed oil and walnut oil are used for salad dressings and stuff like that—but not for high-heat applications. These oils are rich in alpha-linolenic acid (ALA), which is a form of good, anti-inflammatory omega-3 fat.

Flax and walnuts are super-healthy foods to include in your diet for this reason. And their oils are generally thought to be healthy, too. But again, any oil is by definition more processed than the whole food, and that’s not great.

Canola oil is one cooking oil with a significant amount of omega-3 fat, but it still has twice as much omega-6, so the ratio is not outstanding. And there’s also the fact that canola oil, like all processed vegetable oils, contains a small amount of trans fat (source), the worst type of fat of all.

The Actual Healthiest Kind of Oil

I supplement daily with algal oil for omega-3. Read my review of the Future Kind multivitamin here.

Fish oil and algal oil (sometimes written as algae oil) are often taken as omega-3 supplements. These oils contain DHA and EPA, the most valuable forms of omega-3 that are ready to be used by our bodies.

Even Dr. Michael Greger recommends taking 250 mg of yeast- or algae-based DHA as a supplement.

I have still heard some staunch anti-oil gurus suggest that even a fish oil or algal oil omega-3 supplement is a bad idea. Dr. John McDougall has suggested that omega-3 supplementation may increase cancer risk (source), for example.

Personally I’m not convinced, though. I think the weight of evidence suggests that supplemental DHA and EPA are beneficial for brain health and lowering inflammation in the body overall.

Fish oil may have unhealthy levels of mercury or PCB contamination, so algal oil supplements may be the best choice. (Fish get their omega-3 from algae in the first place, so we’re just going lower on the food chain.)

I follow Dr. Greger’s recommendation to take a vegan DHA/EPA supplement from algal oil. Personally, I take a simple multivitamin that includes algal oil—the Future Kind Essential Multi (full review here). I’ve also taken the Zenwise vegan omega-3 (Amazon link) and I had no complaints whatsoever.

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