Vegetable Oils + PUFAs: How do Oxidation + Free Radicals Impact Our Health?

Vegetable Oils + PUFAs: How do Oxidation + Free Radicals Impact Our Health?

In This Article

Are Vegetable Oils Healthy? 

cooking with olive oil

Vegetable cooking oils were once touted as heart healthy replacements for butter and lard. Unfortunately, they are the newest culprit in today’s rising levels of heart disease.1 

In the early 1900s, a new cooking oil was introduced to food manufacturers and the American family. It was stable, cheap, and did not alter taste. Meet soybean oil, which still finds its way into an inordinate amount of processed and packaged foods. 

Soybean oil, like all vegetable oils, is rich in omega-6 polyunsaturated fatty acids and linoleic acid. Linoleic acid is the main fatty acid in omega-6 fatty acids, which is now responsible for 8-10% of energy intake in the Western world.1 

Processed Vegetable Oils to Avoid 

polyunsaturated fats (vegetable oils) pouring
  • canola 
  • soy 
  • sunflower 
  • corn 
  • grapeseed 
  • safflower 
  • rice bran 
  • cottonseed 
  • fake butter spreads like margarine 

Oils that Store in Your Fat 

Sadly, because of the processed nature of these oils, much of it ends up deposited in fat cells. In fact, from 1959 to 2008, the amount of linoleic acid deposited in subcutaneous fat jumped from 9.1% to 21.5%.1  

One 2018 study reports that linoleic acid promotes oxidative stress, oxidized LDL (bad cholesterol), chronic low-grade inflammation, and atherosclerosis, and is likely a major dietary culprit for causing coronary heart disease, especially when consumed in the form of industrial seed oils commonly referred to as “vegetable oils.”1 

The amount of linoleic acid (processed vegetable oils) deposited in fat (belly fat, hips, cellulite) is associated with risk of arterial health issues. Furthermore, high levels of omega-6 fatty acids built up in fat stores will reduce concentrations of heart-healthy long-chain omega-3 fatty acids (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]), most commonly found in fish oils.1 

Vegetable Oils: The Oxidation Equation 

In the early 1900s, before the soybean introduction, vegetable oils were available for culinary use, but they looked much different than today. Seed oils were cold-pressed in dark warehouses and delivered in dark brown bottles in the wee hours of the morning—much like the milkmen we know of today. These oils were so volatile to oxidation that any light exposure would accelerate their rancidity. 

Today, vegetable seed oils are industrially processed and oxidized to such an extent that for commercial cooking oils to have a stable shelf life, all the nutrients and protective antioxidants in the seed are processed out. These vegetable seed oils are boiled to over 400° Fahrenheit, denatured, bleached, and then deodorized because they smell so bad after processing.3,4 Contrary to the oils pressed and sold in dark rooms and dark bottles, today’s seed oils are void of the nutrients that once graced the seeds, so they can be sold 24/7 in clear plastic bottles in fully lit grocery stores.  

Happy excited young chubby red-haired male opening mouth widely while biting bar of chocolate, feeling impatient. Funny Caucasian man in grey t-shirt consuming unhealthy but delicious junk food

Highly processed high linoleic acid vegetable oils are so stable, they use them to preserve food and extend shelf life. You will find them all in packaged food in the middle of your grocery store. Linoleic acids are so fully oxidized that not only are they toxic and damaging to the arterial wall, but intestinal microbes that typically feed on essential fatty acids and fiber won’t touch them. 

Bread, for example, years ago would get hard and stale in just one day, making your local baker a regular stop on your shopping list. Today, breads stay soft for months thanks to highly processed vegetable oils used to extend shelf life—but not your life. 

Beneficial microbes ingest good fats, but if microbes will not eat the processed fats in your bread, your bread will not go bad or mold. But when you eat the processed bread, those same microbes now in your gut won’t eat or digest them either. All the indigestible omega-6 fats end up in the liver to be broken down as toxic waste or stored in your fat as a toxic waste dump.  

Today, gallbladder removal is the most common elective abdominal surgery in America. Gallstones, just one reason the gallbladder fails, affecting 10-15% of Americans, or 20-25 million people.2 

More importantly, why has gallbladder disease risen by 20%+ in the last 30 years? In large part, the answer is oxidized fats.

We recommend "How Much Fat Does Your Gallbladder Need?":

The low-density lipoprotein (LDL) oxidation hypothesis gained traction during the 1980s because it discovered that unoxidized LDL cholesterol does not cause arterial-damaging foam cells. LDL had to become oxidized first in order for atherosclerosis to develop. It was later discovered that oxidized LDL causes toxic effects to the cell, inflammation, endothelial damage to arteries, and foam cell formation, which are all precursors to arterial plaque.1  

Heating PUFAs 

Polyunsaturated fatty acids (PUFAs), omega 3s (predominantly fish oils), 6s, and 9s (predominantly vegetable oils) will all oxidize when heated! Saturated fats (like ghee and coconut oil) and monounsaturated fatty acids (like pure high-quality extra virgin olive oil) are heat stable—yes, you can cook with high quality extra virgin olive oil. 

Heating PUFAs accelerates the free radical cascade of damage and oxidation in the body. In a famous New Zealand study, researchers evaluated arterial blood flow after a fried food meal. They used a blood pressure cuff to see how fast blood vessels would dilate back to normal after ingestion of a meal cooked in used fast food fryer oil. 

The results were dramatic. Four hours after ingesting the meal cooked in one-week-old high omega-6 vegetable oil, they measured how quickly the artery would recover from the pressure of the blood pressure cuff. Before the meal, the vessels dilated normally, but afterwards, there was almost no dilation!4,5 

What kinds of oils are making their way into your body? Hopefully now, armed with this information, you’ll look a little more carefully at processed foods and vegetable cooking oils, and opt instead for fresh foods and oils. They may go bad quicker, but they will keep you healthier. 

We recommend "The Scary Facts About Polyunsaturated Fats":

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Dr. John


  4. Shanahan, C. Deep Nutrition. 228. Flatiron Books. NY pg. 139. 

5 thoughts on “Vegetable Oils + PUFAs: How do Oxidation + Free Radicals Impact Our Health?”

  1. What about rapeseed oil, sesame seed oil, sacha inchi seed oil and goose fat? Doesn’t all omega 3 oil also oxidize in the supermarket bottles (flax and chia)?

    • Sesame seed oil has lignins in it that protect it from heat damage. Eating some is okay. Rapeseed is essentially the same thing as canola oil. And as for flax and chia, I would grind those fresh (or have sprouted flax powder). Not sure about sacha inchi as I’ve never looked into it. High oleic sunflower oil can be okay as it’s similar to olive oil in that it’s made up largely of monounsaturated fats.

      Animal fats such as goose fat are good. The only issue with animal fat from poultry and pigs (not the case with ruminants so much) is that if they are fed a high polyunsaturated fat diet then that will show in their body fat as well. A great reason to know your farmer! I’m currently working on formulating my own feed for our chickens due to the prevalence of vegetable oil in all the available feeds.


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