The Skinny on Fats: Are Vegetable Oils Bad for You?

Many natural health gurus claim that vegetable oils are bad for you, despite mainstream medicine having promoted their benefits for decades. So the Rogue Scientist decided to investigate.

It all started about 10 years ago.

I’d faced stress-related health issues and a friend recommended a naturopathic practitioner located in Boulder, CO, a bastion of alternative medicine.

I’m a health nut and a curious person, so I thought, why not? I’m always up for an experiment. Plus, I’ve personally found that a mixture of non-traditional and mainstream medicine has worked well for me.

I consulted with this woman, and I liked her fine. Her methods were far from scientific, but for the most part she offered some sound advice.

But one thing she told me, and my friend before me? That canola oil is pure garbage and to never consume it.

Fast forward a decade, where I joined a few health-related groups on Facebook. At the mention of canola oil, someone proclaimed how evil it is and posted a link from a questionable source. A debate ensued.

I saw similar examples in these groups as well. Some hated on canola, but many others said that all vegetable oils are bad for you, and claimed these oils are inflammatory. “Inflammation” is a popular buzzword these days because research has shown that it plays a strong role in disease.

I did some searches and sure enough, many natural health gurus (several with big degrees) likened vegetable oils to little more than poison. By contrast, mainstream medicine has told us for decades that vegetable oils are healthy.

So which is it?

I decided to hunker down and find out for myself. It didn’t take long to find myself down a deep rabbit hole.

**If you’re a TLDR (Too Long Didn’t Read) person, no problem. I offer bottom-line summaries at the end of each section and a final list of recommendations at the bottom.

Fats 101: Types of Cooking Oils and Fats

You’d think the study of fats and oils would prove pretty straightforward, but alas… nothing is simple in science. To understand the rest of this article, I offer you some fat basics.

We consume four basic types of oils/fats in our diet, which differ depending on the type of fatty acid each has:

Saturated Fatty Acids

You’ll find these fats in a variety of foods, but animal products such as beef, sausage, bacon, cheese, and dairy have the highest amounts. Cooking fats that are high in saturated fats include:

  • Coconut oil
  • Palm and palm kernel oils
  • Butter
  • Tallow/lard

Research has shown that saturated fats can increase heart disease risk. However, more recent research suggests that saturated fats aren’t necessarily a bad thing if they’re eaten in moderation. What “moderation” means is unclear, and something to explore in another article.

Monounsaturated Fatty Acids (MUFAs)

You’ll find plentiful MUFAs in avocados, nuts, and seeds. Oils high in MUFAs include:

  • Olive oil
  • Peanut oil
  • Canola oil
  • Avocado oil

Overall, research has shown that MUFAs decrease heart disease risk.

Polyunsaturated Fatty Acids (PUFAs)

PUFAs are plentiful in many vegetable sources, including nuts, seeds, and fish. Oils high in PUFAs include:

  • Sunflower oil
  • Safflower oil
  • Corn oil
  • Soybean oil

PUFAs are further divided into two types:

Omega-3 fatty acids: found in fish, flaxseed, and some nuts and oils (e.g. canola).

Omega-6 fatty acids: found in leafy greens, seeds, nuts, and most vegetable oils.

Generally, research has shown that PUFAs decrease heart disease risk. 

Trans Fatty Acids

While trans fats occur in small amounts in some animal foods, most get created in a lab. They add hydrogen to the fatty acids to make the fats solid at room temperature, which gives foods a longer shelf life and (oddly) better taste.

When you see the words “partially hydrogenated” on your snack food’s list of ingredients, that means trans fat.

Foods high in trans fats:

  • Fried foods
  • Packaged baked goods
  • Margarine and shortening
  • Microwave popcorn

Research has shown consistently that trans fats increase risk of heart disease, stroke, and diabetes.

The Supporters: Those Saying Vegetable Oils are Beneficial to Health

Before we tackle the haters, let’s begin with the generally accepted narrative that vegetable oils are good for your health and help prevent heart disease, diabetes, and other health problems. Mainstream medicine has supported this stance for decades, and so has science.

The following three mainstream medical sites that push the vegetable-oils-are-good narrative:

#1: Medical News Today

In this article, MNT states:

An American Heart Association (AHA) report states that unsaturated fats, which include monosaturated and polyunsaturated fats, can reduce the risk of heart disease when people chose to eat them instead of saturated and trans fats.

Research has associated saturated fats with higher levels of low-density lipoprotein (LDL) cholesterol in the blood. LDL cholesterol, which doctors also call bad cholesterol, is a significant risk factor for cardiovascular disease.

There is some debate among researchers about whether or not people can consider coconut oil a healthful addition to the diet.

And:

A group of researchers from the Department of Food Science and Human Nutritional Sciences in Manitoba, Canada, reviewed the evidence for the health benefits of canola oil [a PUFA oil].

Their results demonstrate that people who follow diets they based on canola oil had lower total cholesterol levels compared with those consuming a typical Western diet high in saturated fatty acids.

The researchers suggest that the canola oil could reduce LDL cholesterol levels by an average of 17 percent when they compared it with that of the typical Western diet.

They conclude with:

Choosing oils with a higher level of unsaturated fatty acids may provide the best health benefits.

#2: Harvard Health

The opening statement in an article from this heavy hitter states:

Avoid the trans fats, limit the saturated fats, and replace with essential polyunsaturated fats.

Harvard Health places unsaturated fats (MUFAs and PUFAs) at the top of the fat heap, saying “Healthy fats are liquid at room temperature, not solid.” They go on to state:

Eating polyunsaturated fats in place of saturated fats or highly refined carbohydrates reduces harmful LDL cholesterol and improves the cholesterol profile. It also lowers triglycerides.

Omega-3 fatty acids may help prevent and even treat heart disease and stroke. 

Omega-6 fatty acids have also been linked to protection against heart disease. 

The omega-6 link takes you to a page that sings the praises of these PUFAs and poopoos the notion that too many isn’t good for you.

#3: Healthline

This article also touts the benefits of vegetable oils. For example, it states, “One study found that using safflower oil daily may improve inflammation, blood sugar management, and cholesterol among postmenopausal women with obesity and type 2 diabetes (Trusted Source).

It also offers a useful caveat, one that will matter when we get to the Vegetable Oil Hater section: the healthiness of any vegetable oil may depend on what temperature you use for cooking.

When cooking oils are heated, particularly at high heat, they eventually reach their smoke point. This is the temperature at which the oil is no longer stable and begins to break down.

When oil breaks down, it begins to oxidize and release free radicals. These compounds can have negative health consequences, potentially causing cellular damage that may lead to disease development (12).

Furthermore, oils that reach their smoke point release a substance called acrolein, which can create an unpleasant burnt flavor. What’s more, airborne acrolein may be dangerous to your lungs (3).

BOTTOM LINE

  • Mainstream medicine maintains (with plenty of credible sources) that vegetable oils (i.e. unsaturated fats, including MUFAs and PUFAs) are not only NOT bad for us, they benefit our health by reducing risk for heart disease and other health problems.
  • It may prove beneficial to consider smoke point when selecting an oil for cooking. (We’ll get to that later.)

The Haters: Who Claims Vegetable Oils are Bad for You?

I found a decent number of articles citing the dangers of vegetable oil on your health, but most referenced other, larger sources. I finally nailed down three reasonably high-ranking articles making clear claims about the perils of vegetable oil.

#1: Dr. Mark Hyman

Mark Hyman is a physician and bestselling author, and a big name in health. His specialty is functional medicine, a type of alternative medicine. Hyman claims you should not just reduce vegetable oil consumption, but avoid it altogether.

In this article entitled “Why Vegetable Oils Should Not Be Part of Your Diet,” he calls these oils “highly unstable” and “highly inflammatory,” but offers no evidence of either.

He then goes on to discuss two review studies (published 2010 and 2014), both with Dr. Dariush Mozaffarian (an expert in nutrition science) as an author. Hyman states:

In a 2010 review at Tufts University, Dr. Dariush Mozaffarian concluded there is a clear benefit from cutting out saturated fats and increasing our intake of PUFAs. However in 2014, the very same scientist reviewed all of the literature again. This meta-analysis, which reviewed 72 studies, found no benefit to reducing saturated fats or increasing PUFAs, except for omega 3 fats.

Is it any wonder we are so confused? If the experts can’t even agree and they change their perspective every few years, what are the rest of us to do?

Hyman linked the 2010 study, but not the 2014 study, which I hunted down. I checked out each.

The 2010 paper found “modest” reduction in heart disease risk by replacing saturated fats with PUFAs, but acknowledged more need for research in this area. The 2014 study concludes:

“Current evidence does not clearly support cardiovascular guidelines that encourage high consumption of polyunsaturated fats and low consumption of total saturated fats.”

The problem isn’t that “experts can’t agree.” They reviewed the literature and found a modest result, then reviewed it again and didn’t. This happens often in science, and the message from both of these review studies merely points out that unsaturated fats aren’t necessarily that much better than saturated fats in terms of heart health.

More importantly, the studies don’t point to any type of fat as “bad,” with the exception of trans fats.

Hyman goes on to call omega-6 fats “inflammatory,” claims they “undo” the benefits of omega-3s, and states that too many omega-6s increases risk of inflammatory disease and mental illness, suicide, and homicide. Not a single citation for any of these dramatic claims.  

Finally, he mentions the research of Dr. Joseph Hibbeln, citing the scientist’s stance that overconsumption of omega-6s and underconsumption of omega-3s significantly increases risk for all sorts of disease (he offers a list).

I found some of Hibbeln’s work (check out this study and this one). The studies support increasing omega-3s in those with behavioral disorders rather than providing any evidence that omega-6s are bad.

BOTTOM LINE

Mark Hyman strongly asserts that PUFAs/vegetable oils are bad for you but offers zero evidence to support the claim. What evidence he does provide only argues that saturated fats aren’t necessarily bad and omega-3s may have beneficial effects.

VERDICT: Hyman did not convince me that vegetable oils are bad for you. If anything, he did the opposite.

#2: MindBodyGreen

The mindbodygreen website offers health-related advice that focuses on alternative medicine and holistic health.

In this article, the author lists eight vegetable oils to avoid and cites Cate Shanahan, MD as a source. Shanahan claims, “I think vegetable oils are the No. 1 cause of health problems in this country.”

The proposed eight baddies include corn, canola, cottonseed, soybean, sunflower, safflower, grapeseed, and rice bran oils.

Why these eight? According to Shanahan, two reasons: they’re refined and high in PUFAs, which are “highly unstable.” From the article:

Meaning, when they’re exposed to chemicals in the refining process, they’re stripped of their antioxidants, vitamins, and minerals. Over time, PUFA becomes stored in the body fat, which may lead to inflammation.

She prefers butter and unrefined/cold-pressed oils.

The problem? The article has little in the way of citations (the link above is the only one backing up some pretty broad claims). So, I headed to Shanahan’s website to investigate further.

Cate Shanahan’s Website

On her site, Shanahan equates these eight oils with trans fats and fake/fast/junk foods (every study I’ve found makes it clear that trans fats are bad for your health, PUFAs are not). She says the oils are toxic and get stored in our body fat, that body fat PUFA percentages were only 2-4% in the early 1900s compared to 10-30% today, and that this “makes our body fat prone to inflammation and has disastrous consequences for our overall health…”

The page makes some strong claims… with NO citations. Instead, she offers a link for references, which leads to a different page with a giant, minimally organized data dump of graphs, claims, and links to studies. It would take months to go through it all.

In science, you state your claim and immediately cite empirical evidence that directly supports that claim. You don’t send people off to a data dump and make them sort through it.

To add to that, the top graph on the references page shows an increase in diabetes coinciding with increased vegetable oil consumption over the past several decades. This is a great example of equating correlation with causation, when any number of factors could have caused the rise in diabetes. She also states:

Healthcare professionals for the most part accept the AHA’s [American Heart Association’s] advice without question because they are unaware of the history of the organization’s dependence on funding from companies selling products made with seed-oil. Most healthcare professionals are also unaware of the scientific fraud perpetrated by the men who originally proposed the idea that seed oils are healthy and saturated fats are unhealthy.

When people say things like this, and certainly things like “The AHA will never show you this graph” (see second link), it begins to sound like conspiracy theory, not science.

I did find the idea that refining/processing vegetable oils can impact their nutritional value interesting. However, I could find no evidence for it, other than one science blogger claiming the impacts of refining are real but minimal (no citation).

I also looked into the claim that PUFAs are unstable (i.e. they oxidize to form free radicals). I’ll cover this below (short answer is only in certain situations). 

BOTTOM LINE

Both the mindbodygreen article and Shanahan’s site make strong claims about the ill effects of these eight vegetable oils without citing supporting evidence. Shanahan also seems to veer into conspiracy territory with her claims, further increasing doubt.

VERDICT: This article and Shanahan’s sources did not convince me in the least that vegetable oils are bad for you.

#3: Perfect Keto

Perfect Keto appears to be a blog-based website focused on the keto (ketogenic) diet. The article “Is Vegetable Oil Bad for You? 7 Vegetable Oils to Avoid” was written by a health writer and reviewed by the website’s founder, an alternative medicine practitioner.

The author makes a strong claim up front:

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.

He brings up the fact that vegetable oil consumption rose after saturated fats were declared risky for heath, and provides decent evidence that saturated fat isn’t the evil we’ve been taught to believe. That’s a different article for a different day.

His main argument against vegetable oils — particularly soybean, peanut, corn, canola cottonseed, sunflower, and safflower — revolves around how much linoleic acid they contain. Linoleic acid is an omega-6 PUFA, and the author cites some studies to support his thesis that this fatty acid is inflammatory and unstable.

I didn’t find the cited studies that convincing. One examined mice and argued only that “excessive” linoleic acid induced obesity, preventable by increasing omega-3 intake. The link for the citation supporting the inflammatory nature of linoleic acid was broken. Another link reviews the idea of oxidation in PUFAs, but isn’t an empirical study.

Here’s the thing: this article from Harvard Health states the opposite, that linoleic acid is NOT inflammatory (here is the meta-analysis study the article is based on). A quick search located many studies saying the same thing.

BOTTOM LINE

I applaud this article for including links to actual studies to support the author’s claims (unlike the above two examples). However, as with most articles of this nature, the author has cherry-picked articles to support the argument he’s trying to make (that the PUFA linoleic acid is bad for you) and doesn’t acknowledge that there’s even more research arguing otherwise.

VERDICT: Still not convinced that vegetable oils are bad for you. However, I’m open to the idea that consuming too many of them, especially if not consuming enough omega-3s, could be less than ideal. But I want to see evidence of it, not conjecture.

Refining, Smoke Point, and Oxidation of Vegetable Oils

The oils we eat undergo varying levels of refining before being sold at the grocery store.

Unrefined (virgin) oils undergo less processing and have more flavor; however, they are less stable at high heat. Refined oils have less odor and taste, but prove more stable when cooked at higher temperatures.

All fats have a “smoke point,” a heat level at which they will begin to burn and therefore smoke, which impacts the flavor and potentially the health value of the oil. Refined oils have higher smoke points.

Some of the complaints from the haters regarding vegetable oils revolve around their “instability” (that they can oxidize and create free radicals). This can occur if the oil is heated beyond its smoke point.

Heating oil beyond its smoke point can give food unpleasant taste and smoke up your house, but is it harmful to your health?

One scientist states that the smoke contains acrolein, which can cause changes in your DNA, making it potentially carcinogenic. According to him, it’s a bigger issue for professional cooks rather than people at home who occasional burn their oil.

He also claims that any resulting oxidation and free radicals will affect the oil’s flavor and smell more than your health.

However, other sources claim it’s better to be safe and avoid overheating oil. Choosing the right oil for the job is key — see the smoke point list below.

BOTTOM LINE

Vegetable oils are safe if you choose an oil that can withstand the temperatures you cook at.

When Oils ARE Bad for You

In all my searches for this article, I did find two instances where vegetable oils can prove bad for your health.

  1. When the oil is reheated and reused. This increases free radicals. You may not do this at home, but restaurants might when using deep fryers. The evidence that heating oil repeatedly is bad for you is extensive (start here, here, and here if you like).
  2. Deep frying. Although not as bad for you as repeatedly heated oil, deep frying has its ills too, particularly when fried at high temperatures.

List of Smoke Points for Fats and Oils

If you want to avoid any potential health hazards of overheating oil, choose oils that can handle the temperature you plan to cook at. Here’s a good list.

Fat/OilSmoke Point (F)Smoke Point (C)
Avocado oil (refined)520-570F270-300C
Avocado oil (virgin)375-400F190-205C
Canola oil (refined)400F205C
Coconut oil (refined)400F205C
Coconut oil (virgin)350F175C
Corn oil440F227C
Grapeseed oil390F195C
Olive oil (extra virgin)325-375F165-190C
Olive oil (light/refined)425-465F220-240C
Peanut oil (refined)450F230C
Rice bran oil (refined)490F260C
Safflower oil (refined)510F265C
Sesame oil (unrefined)350F175C
Soybean oil (refined)450F230C
Sunflower oil (refined)440F225C
Vegetable oil400-450F205-230C
Vegetable shortening360F180C
   
Butter300-350F150-175C
Clarified butter (ghee)450F230C
Beef tallow400F205C
Lard370F188C

Spruce Eats has a good list, plus tips for what oils to use depending on if you’re searing, sautéing, deep-frying, or stir-frying.

TLDR and Summary: Health Recommendations for Consuming Fats

Whether you read through this beast or fast-forwarded to this section, I offer a quick list to summarize all I learned when getting sucked into this fats-and-oils rabbit hole.

  • Saturated fats aren’t evil, but don’t overdo it. Focus more on unsaturated fats in your diet.
  • Severely limit consumption of trans fats seen in processed snacks, microwave popcorn, and margarine. They aren’t good for you.
  • Vegetable oils (PUFAs and MUFAs) appear safe and beneficial to health as long as you choose the proper fat for your cooking needs. For higher-temperature cooking, use refined oils to avoid burning and formation of free radicals.
  • I did find some interesting evidence that getting more omega-3s in your diet (and possibly fewer omega-6s), has beneficial effects on health (including mental health). Eat your seafood, flaxseed, walnuts, and canola oil.
  • Minimize deep-fried foods (this one hurts me too, believe me), and avoid consuming fry fat that’s been heated repeatedly.
  • As with most things, it’s best to get fats straight from the source, by eating meat, fish, nuts, seeds, avocado.
  • Try to mix it up with your fats. They all have different benefits and drawbacks.

The Last Word

We all want what’s best for our health. And I like that naturopathic medicine is willing to go beyond the limitations of current research and try things, especially when treating those who have health ailments that mainstream medicine doesn’t know what to do with.

However, it bothers me when health gurus make strong claims about the benefits or evils of a certain food or supplement without evidence. Especially when they influence a lot of people who trust them.

I looked far and wide and could not find evidence that vegetable oils are bad for your health. As such, that refined safflower oil will stay in my kitchen where it belongs.

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The Rogue Scientist

Christie Hartman is a writer and scientist specializing in science-based health. A biology major as an undergrad, she completed her PhD in behavioral genetics at the University of Colorado Boulder. Before starting her writing career, she worked as a scientist and professor at CU’s School of Medicine, where she studied the genetic contributions to substance abuse and antisocial behavior.

3 thoughts on “The Skinny on Fats: Are Vegetable Oils Bad for You?”

  1. Thanks for the Skinny on oils. I have dedicated file space for your articles. Thanks for all you do. Skip..

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