Are Vegetable and Seed Oils Bad for Your Health?

December 24, 2020

Important Points:

  • Industrial Seed Oils
  • Hydrogenated fat
  • Omega 6
  • Omega 3
  • Linoleic acid
  • Animal Fats

Are Vegetable and Seed Oils Bad for Your Health?

The consumption of vegetable oils has increased dramatically in the past century. Contrary to what we’ve been told, industrial seed oils such as soybean, canola, and corn oils are not “heart healthy” or otherwise beneficial for our bodies and brains; in fact, plenty of research indicates that these oils are making us sick. In this article, we take you through the industrial seed oil history, the adverse health effects of consuming these oils, and what dietary fats you should eat instead.

1. What Are Seed Oils?

Industrial seed oils are highly processed oils extracted from soybeans, corn, rapeseed (the source of canola oil), cottonseed, and safflower seeds. They were introduced into the American diet in the early 1900s.

2.  How Are Industrial Seed Oils Made?

The general process used to create industrial seed oils is anything but natural. The oils extracted from soybeans, corn, cottonseed, safflower seeds, and rapeseeds must be refined, bleached, and deodorized before they are suitable for human consumption.

  1. First, seeds are gathered from the soy, corn, cotton, safflower, and rapeseed plants.
  2. Next, the seeds are heated to extremely high temperatures; this causes the unsaturated fatty acids in the seeds to oxidize, creating byproducts that are harmful to human and animal health.
  3. The seeds are then processed with a petroleum-based solvent, such as hexane, to maximize the amount of oil extracted from them.
  4. Next, industrial seed oil manufacturers use chemicals to deodorize the oils which have a very off-putting smell once extracted. This deodorization process produces trans fats.
  5. Finally, more chemicals are added to improve the color of the industrial seed oils.

Altogether, industrial seed oil processing creates an energy-dense, nutrient-poor oil that containschemical residues, trans fats, and oxidized byproducts.

3. Why are they bad for you?

Linoleic Acid Could be Increasing Our Risk of Obesity and Related Health Problems

From experiments in mice, increasing the intake of linoleic acid from 1% to 8% may result in brain signals that stimulate greater food consumption and promote body fattening. Greater intake of linoleic acid seems to mask a sense of fullness and to increase the size of fat cells

  •  Vegetable Oils Contain an Unnatural Amount of Omega-6 Fats

When It Comes to Omega-6, quality matters. While industrial seed oils are high in omega-6, there are also plenty of whole, fresh foods that naturally contain omega-6 fatty acids including nuts, poultry, and avocados.

Essential fatty acids are polyunsaturated fats (PUFA) that we humans cannot make ourselves and must, therefore, consume in our diets. They come in two varieties: omega-6 fatty acids and omega-3 fatty acids. Upon consumption, omega-6 fatty acids give rise to arachidonic acid and potent metabolites that are primarily pro-inflammatory in nature including prostaglandin E2 and leukotriene B4. Omega-3 fatty acids such as ALA, EPA, and DHA, on the other hand, give rise to anti-inflammatory derivatives.

A delicate balance between omega-6 and omega-3 fattyacids must be maintained in the body to promote optimal health. A high intake of omega-6 fatty acids, combined with low omega-3 intake, leads to an imbalance in pro-inflammatory and anti-inflammatory mediators producing a state of chronic inflammation that contributes to numerous chronic disease processes.

  • Vegetable Oils are Unnaturally Produced, Highly Refined, and Extracted Using Heat and Chemicals

Factory-processed PUFA oils are created through measures of high heat and extreme pressure exposing the oil to all sorts of oxidative damage, polished off with a good dumping of chemical solvents to get every last bit of that profit-producing oil out of the seeds, or corn, or soy. Some of the chemical (usually hexane) remains, and yet another chemical is added to deodorize the rancid PUFA oil’s stench. In that process, the small amount of omega-3 present in oils like canola, actually transforms into trans fatty acid. And finally, carcinogenic BHT and BTA are added as chemical preservatives, since any naturally-occurring preservative substances, such as antioxidant vitamin E which were once naturally found in the food, have been thoroughly killed off in processing.  

  • Vegetable Oils Contribute to Excess Inflammation and Free Radical Damage. 

Polyunsaturated Fats are very fragile and oxidize very easily. Free-radical forming oxidation of the PUFA happens when it is exposed to heat, light, or oxygen. This is pretty hard to avoid that when you’re cooking with these fragile oils and most restaurants exclusively use these oils not only for cooking, but for extreme high-heat frying.

Excessive inflammation in the body from PUFAs happens because of the presence of free radicals formed in the processing of the industrial oils (like vegetable and canola), which renders them rancid. Free radicals, unattached and needing a place to land, attack cell membranes and red blood cells and cause damage to DNA and RNA strands leading to cellular mutations in the body’s tissues. In skin, it causes wrinkles and premature aging. In blood vessels, they cause the buildup of plaque. In tissues and organs, it can set the stage for tumors to form. You get the idea. Free radicals are bad, bad news, and they’re ever-abundant in industrial PUFA oils. 

  •  Many Vegetable Oils are Hydrogenated and Can Be Filled with Trans Fats.

PUFA’s are at their very worst when they are partially or fully hydrogenated. This chemical process takes place in factories, and it’s used to make PUFA’s solid at room temperature and more “shelf stable”. Trans fat is the artery-clogging fat that is formed when vegetable oils are hardened to make margarine, vegetable shortening, and often vegan butters and cheeses, etc., as well. Trans fats prevent the synthesis of prostacyclin which is necessary to keep your blood flowing. When your arteries cannot produce prostacyclin, blood clots form, and you may succumb to sudden death.

4.  What Health Conditions are Linked to Industrial Seed Oils?

  • Asthma: Consuming industrial seed oils may increase your risk of asthma. A high intake of omega-6 fatty acids, such as those present in industrial seed oils, relative to omega-3 fatty acids increases pro-inflammatory mediators associated with asthma.
  • Autoimmune Disease: Industrial seed oils may promote autoimmunity by raising the body’s omega-6-to-omega-3 ratio and by increasing oxidative stress and chronic inflammation.
  • Cognition and Mental Health: Industrial seed oils are particularly harmful to the brain. A high omega-6-to-omega-3 fatty acid ratio predisposes individuals to depression, anxiety, cognitive decline, and dementia, and canola oil consumption is linked to worsened memory and impaired learning ability in Alzheimer’s disease. Trans fats, which end up in industrial seed oils unintentionally as a consequence of chemical and heat processing, and intentionally during the process of hydrogenation, are associated with increased risks of dementia and, interestingly, aggression.
  • Diabetes and Obesity: Research in mice indicates that consuming high levels of linoleic acid, the primary fatty acid in industrial seed oils, alters neurotransmitter signaling, ultimately increasing food consumption and weight gain. In mice, a diet high in soybean oil induces obesity, insulin resistance, diabetes, and fatty liver disease, and some animal research also suggests that canola oil may cause insulin resistance.
  • Heart Disease: Researcher James DiNicolantonio has presented a theory called the “oxidized linoleic acid theory of coronary heart disease” that links the consumption of linoleic acid-rich industrial seed oils with cardiovascular disease.
  • IBS and IBD: Research suggests that industrial seed oils may harm gut health, contributing to conditions such as irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD). In one study, mice fed a diet high in omega-6 fatty acids from corn oil experienced increases in pro-inflammatory gut bacteria; these changes favor the development of gastrointestinal pathologies among many other chronic diseases.
  • Inflammation: A high omega-6 intake from industrial seed oils promotes chronic inflammation. The consumption of both partially hydrogenated industrial seed oils and non-hydrogenated soybean oil is associated with elevations in C-reactive protein, TNF-alpha, and interleukin-6, which are biomarkers of systemic inflammation.
  • Infertility: Approximately 9 percent of men and 11 percent of women in the United States have impaired fertility. While many factors are contributing to soaring rates of infertility, one overlooked cause may be our high consumption of industrial seed oils. Infertile men exhibit a significantly elevated omega-6-to-omega-3 fatty acid ratio compared to fertile men. In animal studies of female mammals, a high intake of omega-6 fatty acids causes poor reproductive outcomes.
  • Macular Degeneration: Industrial seed oils may be harmful to the eyes. A high intake of omega-6 fatty acids increases the risk of age-related macular degeneration, an eye disease that causes progressive vision loss and eventual blindness. Imbalanced levels of omega-6 consumption may contribute to eye problems by promoting inflammation and by displacing the omega-3 fatty acid DHA which is crucial for vision.
  • Osteoarthritis: In individuals with osteoarthritis, there’s an association between omega-6 fatty acids and the presence of synovitis, an inflammation of the membrane that lines joint cavities. Conversely, an inverse relationship has been found between omega-3 fatty acid consumption and cartilage loss in the knee as indicated by MRI. Since industrial seed oils contribute a large amount of omega-6 fatty acids to the diet, avoiding these oils may be beneficial for those with or at risk of osteoarthritis.

5. Which Oils Should You Use for Cooking?

  • Coconut Oil
  • Tallow/ Suet (beef fat)
  • Lard/Bacon Fat (pork fat)
  • Butter
  • Ghee
  • Goose, Duck or Chicken Fat
  • Extra-Virgin Olive Oil*
  • Avocado Oil*
  • Palm Oil**
  • Other fats (not necessarily for cooking, but essential to good health) include meats, eggs, dairy, and fish (nuts are also good in moderation as they have a high level of polyunsaturated fats).

* olive oil and avocado oil are both high in monounsaturated fats which are moderately stable so they are best used in non-heat or low heat, avoid extreme high-heat cooking.  They are also great in salad dressings, homemade mayonnaise, for drizzling, etc.


You can tell if particular oil is chemically processed by simply reading the label.

AVOID all fats, oils, and the products that contain either of them if the following processing terms are listed ANYWHERE on ANY food label:

  • Refined
  • Hydrogenated
  • Partially-Hydrogenated
  • Cold-PROCESSED (do not confuse this trick phrase with Cold-PRESSED)

INSTEAD, look for these safer processing terms on your fat/oil labels:

  • Organic
  • First-cold pressed or Cold-Pressed Expeller-Pressed
  • Unrefined
  • Extra Virgin

6. The Bottom Line

If optimal health is your goal, then industrial seed oils have no place in your diet. Instead, cook with traditional animal fats, get your omega-6s from whole food sources such as nuts and poultry, and balance things out with omega-3 fatty acids from seafood, shellfish, and fish oil.

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