Healthy Food & Life: The Unhealthy Truth About Vegetable Oils
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The Unhealthy Truth About Vegetable Oils

bottle of vegetable oil

When someone first starts eating a whole food plant-based diet, one of the first questions they ask is why vegetable oils are avoided. Despite all the talk that olive oil is a healthy fat, it is actually unhealthy. And it’s not only olive oil, but all vegetable oils that are unhealthy. Vegetable oils keep us from losing weight and cause health issues. Find out exactly why they are unhealthy and what they do to your body.

Vegetable oils include canola oil, palm oil, sunflower oil, sesame oil, corn oil, safflower oil, peanut oil, olive oil, and coconut oil. These vegetable oils are what you will find in processed foods, packaged foods, fast foods, junk foods, baked goods, desserts, and restaurant foods.

I would guess that every package or jar of food in your home has some kind of vegetable oil in the ingredients.

Why Vegetable Oils Are Unhealthy

The first question I get asked about a plant-based diet is why vegetable oils aren’t allowed.

The easiest answer is that they are not a whole food; they are a highly refined and processed food. Secondly, they are very bad for our health. So, the next question is why vegetable oils are bad for our health.

This is why vegetables oils should be avoided in our diet:

  • Too high in fat, especially high in saturated fat
  • Causes atherosclerosis or hardening of the arteries leading to heart disease.
  • Damages the endothelial cells of the arteries and blood vessels reducing the body’s ability to produce nitric oxide.
  • Have more than twice the calories per gram than protein or carbohydrates do, causing weight gain or hindering weight loss.

Chemicals in Vegetable Oils

In order to get oil from plants, they must undergo a process that includes using chemicals. First, the oils are extracted using high temperatures that include toxic, petroleum-derived chemicals such as hexane.

Heating these oils to such high temperatures can cause them to oxidize and become rancid before they even get to the store.

These oils are then are degummed, bleached and further refined at high temperatures. At this stage, more chemicals are used to improve the color of the oils.

And finally, the vegetable oils are deodorized to get rid of the chemical smell.

And if you want a solid oil product, you will have to hydrogenate it. You will find solid hydrogenated oil in many of the fake butter products, which you should also avoid.

To make things worse, some of these vegetable oils come from genetically modified plants like canola from rapeseed and corn oil from corn. And most if not all are heavily sprayed with pesticides.

Only extra virgin olive oil does not go through such a treatment process. But you will rarely see EVOO in packaged food ingredients. The majority of vegetable oils you will see in food are canola oil, corn oil, and palm oil. 

Vegetable Oils Damage Blood Vessels

Vegetable Oils are fat and a diet with too much fat causes atherosclerosis or hardening of the arteries, which is a buildup of plaque, fat, and cholesterol on the inside walls of the arteries. This plaque can lead to heart disease and heart attacks.

The blood vessels of our cardiovascular system are lined with endothelial cells. These endothelial cells are important in the formation of new blood vessels, proper blood clotting, and creating nitric oxide.

Nitric oxide causes blood vessels to dilate, increases blood flow and prevents platelets from sticking to the blood vessel walls. If the endothelial cells are impaired, less nitric oxide is produced, reducing the dilation of the vessels.

Vegetable oils and a high-fat diet damage the endothelial cells, and damaged or impaired endothelial function is a distinctive characteristic of vascular disease, which can lead to the development of atherosclerosis.

Studies have found that within hours of ingesting a meal with added vegetable oils (or saturated fat) arteries stiffen and the ability to dilate is impaired, due to the reduced nitric oxide.

A study in 1999 measured Flow-mediated vasodilation (FMD) after the ingestion of high-fat meals and found: 
“A 3-hour decline in FMD after subjects ingested a traditional meal of a hamburger and fries or cheesecake. Olive oil was found to have the same impairment to endothelial function as the rest of these high-fat meals.” 1, 2
A 2007 study found showed a similar effect on endothelial function after the ingestion of olive oil, soybean oil, and palm oil. 3

Vegetable Oils Cause Weight Gain

Vegetable oils were not readily available in the early 1900s and canola oil was only approved for use in 1985. Corn oil consumption has skyrocketed from zero in 1900 to approximately 2 pounds per person, per year.

Low-carb proponents like to say that the obesity epidemic started with the low-fat movement of the 1980s. That is not an accurate statement, considering the rise in obesity mirrors the big increase in the use of vegetable oils as you can see in the following chart.
Vegetable oil consumption chart
Source: Stephan Guyenet - USDA Economic Research

As previously mentioned, oil is fat and fat has more than twice the calories than either protein or carbohydrates do. Just one tablespoon of oil has 120 calories and 14 grams of fat. The average American has (at least) 3 tablespoons of oil per day in cooking, pastries, salads, breads, fast foods, processed foods, health bars, and junk foods.

That is an extra 360 empty calories per day or 131,400 empty calories per year. That equals 37.5 extra pounds per year. So if you’re wondering why your waist keeps expanding, the amount of oil you have each day is a good place to look.

Unhealthy Omega 6 in Vegetable Oils

Anyone eating a standard western diet is already getting too much omega-6 in their diet, and that is not healthy. A healthy omega-6 to omega-3 ratio should be 4:1 and closer to 2:1.

All vegetable oils have a lot of omega-6 and not much omega-3. For example, olive oil has an omega-6 to omega-3 ratio of 10:1, and that is too high.

Considering the standard western diet is high in vegetable oils, the average omega-6 to omega-3 ratio is 15:1 and as high as 30:1. This is one of the reasons for the increase in chronic illnesses.

Of course, we continue to hear how we all need to eat more fish or take fish oil pills that are high in omega-3.

It is much easier and healthier to lower the amount of omega-6 in the diet since both omega fatty acids compete with each other. Eating less omega-6 in your diet would automatically increase the amount of omega-3 in your body.

What About Olive Oil Health Claims?

First of all, many of these studies are funded by the olive oil industry. And secondly, numerous studies compare olive oil to something worse, like lard for example. When they find olive oil isn’t as bad as lard, all we hear is that olive is healthy.

All this does is exchange something very unhealthy to something less unhealthy. But the bottom line is that they are both unhealthy.

The main health benefit in olive oil comes from the monounsaturated fat, oleic acid, found in olive oil. Oleic acid is an omega-9fatty acid. Studies have found oleic acid to lower the bad cholesterol (LDL) and reduce inflammation, which is where the heart health claims come from.

Any health claims about olive oil can only be applied to pure extra virgin olive oil (EVOO) which retains a fraction of the phytochemicals and polyphenols. All other olive oils are just as processed as other vegetable oils, and that processing removes all antioxidants and health benefits there might have been.

There is no need to consume vegetable oils for oleic acid when you can easily get it from whole healthy foods such as:

  • Nuts and nut butter made from almonds, cashews, and pecans
  • Chia, sesame, and pumpkin seeds
  • Avocados
  • Olives

Another health claim concerning olive oil is that it contains polyphenols, which are considered anti-inflammatory. Studies that find the Mediterranean diet to be a healthy diet assume it is the olive oil. But more recent studies have found it is the vegetables, fruits, and nuts that give this diet its health benefits.

You can get plenty of healthy polyphenols in your diet from foods like:

Vegetable Oils Bottom Line

The bottom line is that vegetable oils, including olive oil and coconut oil, are nothing but pure fat. If there are any healthy nutrients in these vegetable oils, it is negated by the damage they do to our arteries, blood vessels, cardiovascular system, our weight, and our overall health.

Now you know exactly why you should avoid all foods with vegetable oil in them. And this includes the new so-called plant-based fake foods like the Impossible Burger, Beyond Meat and the rest of the oily fake foods. If you eat too many of these processed and oily foods, you could become an unhealthy vegetarian.

About the Author

Sam Montana is a certified Food Over Medicine instructor from the Wellness Forum Health Center and certified in optimal nutrition from the Harvard T.H. Chan School of Public Health.

© 2019 Sam Montana/Healthy Food and Life


[1] UC Davis Integrative Medicine: Flow Mediated Dilation (FMD): A noninvasive method to test endothelial function is which uses an ultrasound to measure flow-mediated changes in the diameter of the brachial artery.
[2] PubMed: Brachial artery ultrasound: a noninvasive tool in the assessment of triglyceride-rich lipoproteins.
[3] PubMed: Olive, soybean and palm oils intake have a similar acute detrimental effect over the endothelial function in healthy young subjects.
The Unhealthy Truth About Vegetable Oils

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