Experts have presented several dietary culprits as possible explanations for the rapidly rising rates of chronic disease in industrialized nations, including sugar and saturated fat. However, one commonly consumed food found in the diets of millions has received surprisingly little attention—industrial seed oils.

What Are Industrial Seed Oils?

In fact, industrial seed oils, the highly processed oils extracted from soybeans, corn, rapeseed (the source of canola oil), cottonseed, and safflower seeds, were only introduced into the American diet in the early 1900s. How, then, did these oils come to occupy such an influential position not only in the Standard American Diet but in “”Westernized” diets around the world? The story is strange indeed.

In 1870s Cincinnati, two soapmakers—William Procter and James Gamble—decided to enter into business together. While soap had historically been made from rendered pork fat, Procter and Gamble were an innovative pair and decided to create a new type of soap from vegetable oils. Around the same time, oil was discovered in Pennsylvania; it quickly displaced cottonseed oil, which had long been used for lighting, as a fuel source. Cottonseed oil was consigned to the status of “toxic waste” until the enterprising Procter & Gamble realized that all that unwanted cottonseed oil could be used to produce soap. But there was another plus that appealed to their business sensibilities: the oil could be chemically altered via a process called “hydrogenation” to turn it into a solid cooking fat that resembled lard. That’s how an oil formerly classified as “toxic waste” became an integral part of the American diet when Crisco was introduced to the market in the early 1900s.

Soon, other vegetable oils followed. Soybeans were introduced to the United States in the 1930s, and by the 1950s, it had become the most popular vegetable oil in the country. Canola, corn, and safflower oils followed shortly after that. The low cost of these cooking oils, combined with strategic marketing on the part of the oil manufacturers, made them wildly popular in American kitchens even though their use was unprecedented in human history.

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. The deodorization process produces trans fats, which are well known to be quite harmful to human health.
  5. Finally, more chemicals are added to improve the color of the industrial seed oils.

From Toxic Waste to “Heart Healthy”: The History of Seed Oils

How did industrial seed oils go from being classified as “toxic waste” to enjoying the title of “heart healthy” fats? The story involves a scandalous combination of donations to medical organizations, dubious scientific research, and unsubstantiated marketing claims.

In the late 1940s, a small group of cardiologists who were members of the still somewhat new American Heart Association received a $1.5 million donation from Procter & Gamble; thanks to this generous infusion of cash from the makers of Crisco, the AHA now had sufficient funding to grow its national profile as a physician’s organization dedicated to heart health. It also were quick to endorse industrial seed oils, more kindly referred to by now as “vegetable oils,” as a healthier alternative to traditional animal fats.

Around the same time, an ambitious physiologist and researcher named Ancel Keys introduced his diet–lipid hypothesis, in which he presented data that seemed to suggest a link between saturated fat and cholesterol intake and heart disease. Since animal fats are a rich source of dietary saturated fat and cholesterol, they quickly became the object of his derision. Citing animal fats as “unhealthy,” Keys instead recommended the consumption of polyunsaturated fatty acids (PUFAs), which preliminary research had associated with reductions in cholesterol and the risk of heart disease. Keys’ conclusions were in line with the industrial seed oil industry’s motives—to get people to eat more seed oils! Soon, ads for “heart healthy” margarine (a solid form of vegetable oil) and other seed oils became commonplace, and healthy, traditional fats were all but forgotten.

While Keys’ lipid hypothesis is now understood to be based upon faulty research, his ideas nonetheless permeated the medical community. (2) Soon, many medical organizations, including the National Cholesterol Education Program and the National Institutes of Health, had hopped aboard the anti-animal fat train, echoing the AHA’s advice that people should avoid animal fat and instead consume polyunsaturated vegetable oils such as Crisco and other shortenings, soybean oil, and corn oil. This confluence of events and mutual interests led to the sweeping replacement of natural dietary fats such as lard and butter with unsaturated industrial seed oils, indelibly changing the shape of the American (and eventually, the global) food landscape.

Only in recent years has the validity of the health claims associated with industrial seed oils been seriously called into question. A 2014 meta-analysis found no benefit to overall health from reducing saturated fats or increasing PUFAs from vegetable oils. Furthermore, the evidence does not support current dietary guidelines urging people to replace saturated fats with vegetable oils. 

Six Reasons Industrial Seed Oils Are Terrible for Your Health

There are six main problems with industrial seed oils:

  1. The consumption of industrial seed oils represents an evolutionary mismatch.
  2. Eating industrial seed oils raises our omega-6-to-omega-3 fatty acid ratios, with significant consequences for our health.
  3. Industrial seed oils are unstable and oxidize easily.
  4. They contain harmful additives.
  5. They’re derived from genetically modified crops.
  6. When industrial seed oils are repeatedly heated, even more toxic byproducts are created.

1. They’re an Evolutionary Mismatch

Industrial seed oils, like refined sugar and excess calories, also represent an evolutionary mismatch. Up until the 1900s, humans did not consume industrial seed oils. From 1970 to 2000, the average consumption of one industrial seed oil, soybean oil, skyrocketed from a mere four pounds per person per year to a whopping 26 pounds per person per year!

Today, linoleic acid, the primary fatty acid in industrial seed oils, accounts for 8 percent of our total calorie intake; in our hunter–gatherer ancestors, it accounted for only 1 to 3 percent of total calories. Researchers who are wise on the topic of evolutionary mismatch posit that our bodies just aren’t designed to handle such a massive consumption of linoleic acid. As a result, our high levels of industrial seed oil consumption are causing our health to suffer.

2. They Have an Imbalanced Omega-6-to-Omega-3 Ratio

Essential fatty acids are polyunsaturated fats 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 fatty acids must be maintained in the body to promote optimal health. The ancestral ratio of omega-6 to omega-3 is 1 to 1. Westernized diets, however, greatly exceed this balance, with omega-6 to omega-3 ratios in the range of 10 to 1 to 20 to 1. (8) 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. This imbalance produces a state of chronic inflammation that contributes to numerous chronic disease processes.

3. Industrial Seed Oils Are Highly Unstable

The polyunsaturated fatty acids in industrial seed oils are highly unstable and oxidize easily upon exposure to heat, light, and chemical inputs. When industrial seed oils are exposed to these factors, two harmful substances—trans fats and lipid peroxides—are created. Trans fats are well known for their role in the development of cardiovascular disease and type 2 diabetes; in fact, for every 2 percent increase in calories from trans fats, your risk of heart disease is nearly doubled! Lipid peroxides, on the other hand, are toxic byproducts that damage DNA, proteins, and membrane lipids throughout the body. The accumulation of lipid peroxides in the body promotes aging and the development of chronic diseases.

4. They’re Full of Additives

Because the fatty acids in industrial seed oils are so unstable, synthetic antioxidants are added in an attempt to prevent oxidation and rancidity. Unfortunately, these synthetic antioxidants come with problems of their own. The synthetic antioxidants BHA, BHT, and TBHQ have endocrine-disrupting, carcinogenic, and immune-disrupting effects. Also, TBHQ has been found to increase the IgE (immunoglobulin E) response to food allergens, setting off a release of antibodies, and may thereby promote the development of food allergies.

5. Industrial Seed Oils Come from Genetically Modified Plants

In addition to being nutrient poor and full of unsavory chemicals and toxic byproducts, the overwhelming majority of industrial seed oils are derived from genetically modified plants. In fact, the plants used to make industrial seed oils comprise the top genetically modified crops—corn, soy, cotton, and rapeseed. In the United States, 88 percent of corn, 93 percent of soy, 94 percent of cotton, and 93 percent of rapeseed crops are genetically modified. Few studies have been conducted on the long-term safety of consuming genetically modified foods, giving us yet another reason to avoid consuming industrial seed oils.

6. They’re Often Repeatedly Heated (And Extra Toxic)

As if industrial seed oils weren’t already bad enough for our health, restaurants and home cooks frequently engage in a practice that further magnifies their harmful effects—they repeatedly heat industrial seed oils. While the habit of reusing industrial seed oils over and over (typically in large deep-fryers, in the case of restaurants) reduces costs, it results in an oil that is chock-full of toxic byproducts.

The repeated heating of industrial seed oils depletes vitamin E, a natural antioxidant, while inducing the formation of free radicals that cause oxidative stress and damage DNA, proteins, and lipids throughout the body. These harmful effects explain why repeatedly heated industrial seed oils are associated with high blood pressure, heart disease, and intestinal and liver damage.

How So-Called “Healthy” Seed Oils Are Making Us Sick

Contrary to what many health organizations have been telling us for years, industrial seed oils are not healthy foods. Rather, their consumption is associated with a variety of health problems.


Eating 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.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

Are industrial seed oils making us overweight and diabetic? The science certainly seems to suggest so. 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 fat mass. In mice, a diet high in soybean oil induces obesity, insulin resistance, diabetes, and fatty liver disease. Animal research also suggests that canola oil may cause insulin resistance.

Human studies also point to the effects of industrial seed oils on diabetes and obesity, especially in children. A maternal diet high in omega-6s compared to omega-3s is associated with an increased risk of obesity, a major risk factor for diabetes, in children. A childhood diet with a high omega-6-to-omega-3 ratio may also lead to insulin resistance, prediabetes, and obesity in adulthood.

Heart Disease

Contrary to what the AHA has been telling us for the past 100 years, industrial seed oils are not good for our hearts! In fact, oxidized fatty acids from industrial seed oils appear to play a pivotal role in the development of cardiovascular 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. His theory goes like this:

  • Dietary linoleic acid from industrial seed oils is incorporated into blood lipoproteins.
  • The instability of linoleic acid increases the likelihood of lipoproteins oxidizing.
  • Oxidized lipoproteins are unable to be recognized by their respective receptors throughout the body and instead activate macrophages, which initiate foam cell formation, atherosclerosis, and cardiovascular disease.

Industrial seed oils also contribute to cardiovascular disease by increasing the omega-6-to-omega-3 ratio. A high omega-6-to-omega-3 ratio is an established risk factor for cardiovascular disease because excess omega-6 has pro-inflammatory and prothrombotic effects on the vascular system. Finally, another emerging theory suggests that canola and soybean oils may contribute to cardiovascular disease by inhibiting processes involving vitamin K2, which is essential for heart health.


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.

Human studies also suggest a link between industrial seed oils and GI conditions. Women with IBS demonstrate significantly elevated levels of arachidonic acid, an omega-6 fatty acid abundant in industrial seed oils, and pro-inflammatory PUFA metabolites, compared to healthy controls. Furthermore, an imbalance between omega-6 and omega-3 fatty acids is correlated with IBD.

These findings suggest that consuming high levels of omega-6 fatty acids alters the gut microbiota and promotes gastrointestinal inflammation, thereby contributing to the development of IBS and IBD. Since industrial seed oils are the most abundant source of omega-6 fatty acids in the Standard American Diet, it stands to reason that people with IBS and IBD should avoid these oils and instead consume natural fats from olive oil, coconut oil, wild seafood, nuts and seeds, and healthy animal fats.


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.


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. (44) 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.


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.

How to Avoid Industrial Seed Oils

The first step in banishing industrial seed oils from your diet is to clean out your pantry and get rid of any bottles of canola, corn, cottonseed, soybean, sunflower, safflower, or peanut oils you have in your kitchen. These oils are not “healthy,” despite misleading claims that may appear on their labels.

Step number 2 is to stop eating processed foods, as these are a significant source of industrial seed oils. Also try to reduce your consumption of restaurant foods, which are typically cooked in repeatedly heated industrial seed oils.

Finally, step 3 is to avoid eating grain-fed meat, to the extent you can. There is evidence to suggest that grain-fed animals may accumulate the toxic byproducts of industrial seed oils, which comprise a large part of their diet, in their meat; when you eat this meat, you too may become a repository for lipid peroxides and other harmful byproducts of industrial seed oils.

by Chris Kresser, M.S.

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