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Is Vegetable Oil Bad for You? The Science Behind the Worst Food in Human History

By Liam McAuliffe Published on

Is vegetable oil bad for you? In a word, yes. But we’d never expect you to just take our word for it.

Together we’ll follow the science and explore the various ways that vegetable oil wreaks havoc on our physical health, mental health, and the health of our planet. 

Most of these negative impacts are ignored and hidden by popular media and mainstream nutrition. It’s high time to pull back the curtain on this devastating dietary and agricultural trend. 

Table of Contents

What are Vegetable Oils?

“Vegetable oils” is a somewhat misleading name. Most vegetable oils are actually extracted from seeds and grains in an energy-intensive industrial process. Popular so-called vegetable oils include: 

  • soybean oil
  • corn oil
  • sunflower oil
  • safflower oil
  • canola oil
  • peanut oil
  • rice bran oil
  • grapeseed oil
  • cottonseed oil

Though nonexistent for the vast majority of human dietary evolution, vegetable oils are in nearly all processed foods, used as a cooking oil at most restaurants, and hidden within processed foods billed as “healthy” including popular alternative oat, almond, and soy “milks”.

A treasure trove of tips for fertility and for a healthy body and mind

Why Vegetable Oil is Bad for You: Fast Facts

The question, “is vegetable oil bad for you?” is more important than ever. Here’s a rundown of why: 

  • Rates of chronic inflammatory diseases like heart disease, asthma, cancer, and diabetes have increased 700% since 1935. 

graph of chronic disease rates in america

  • Today 6 in 10 Americans have a chronic inflammatory disease
  • Heart disease is the leading cause of death worldwide
  • Yet we are smoking less, drinking less, and exercising more
  • We’re eating more so-called “healthy” fruits and vegetables and less red meat
  • We’re consuming less healthy, yet demonized saturated fat and salt
  • As a replacement for saturated fats from whole food animal sources, vegetable oil now accounts for 20% of our daily calories

American consumption of vegetable oil

graph showing global consumption of vegetable oil

 

  • From 1909 to 1999, the per capita consumption of vegetable oils in America and across the globe have increased by over 2000 percent
  • Vegetable oils have been shown to increase risk of death by 62%. This is a greater effect than heavy drinking or moderate smoking
  • Worldwide, vegetable oils are a leading driver of deforestation and climate change
  • Vegetable oils emit more greenhouse gases per kilogram than any other major crop
  • Vegetable oils account for up to 30% of global agricultural land use, but provide less than 0.01% of our vital micronutrients

If we’re following mainstream health guidelines to eliminate saturated fats and eat more plant foods, then, why are rates of chronic inflammatory diseases surging? 

What’s the single variable increasing alongside the diseases that kill the most people across the modern world? 

Vegetable oil! 

But correlation does not equal causation. So let’s explore the science. 

The Israeli Paradox

The Israeli paradox offers an insightful frame for investigating the question, is vegetable oil bad for you? 

Israeli people consume a diet that is almost perfectly aligned with the recommendations of U.S. nutritional “experts”. 

The Israeli diet is low in total fat and saturated fat, and their intake of PUFA-rich vegetable oils is higher than the amount consumed in other Western countries. 

Yet, their rates of cardiovascular disease, type 2 diabetes, and other modern illnesses are on par with the US. And their cancer rates, especially among women, are higher. 

This quandary of a population following dietary recommendations while exhibiting negative health markers has led many researchers to suggest that the high intake of inflammatory Omega-6 PUFA from vegetable oils is to blame.

Linoleic Acid in Vegetable Oil

LA in Vegetable Oil

Most vegetable oils are high in an Omega-6 PUFA called linoleic acid, making them a highly inflammatory food

Linoleic acid is a precursor for a pro-inflammatory molecule called arachidonic acid. 

Arachidonic acid is itself the precursor for a biological pathway that creates over twenty pro-inflammatory eicosanoids. 

Eicosanoids are molecules that signal the body’s immune system to react to perceived damage. They are at the root of many chronic inflammatory diseases.

Without a balancing anti-inflammatory influence from Omega-3 PUFA, these eicosanoids can trigger: 

Autoimmune diseases are characterized by an overreaction of your body’s own immune system resulting in damage to healthy tissues.

The following clinical studies support the hypothesis that vegetable oil is bad for you and likely a key factor in the rise of modern diseases including: 

  • Cancer
  • All-cause mortality (Death)
  • Heart Disease
  • Infertility 
  • Obesity
  • Mood disorders including depression and anxiety
  • Neurodegenerative disorders including Alzheimer’s and Parkinson’s disease

Cancer

Vegetable and seed oils have been shown to cause: 

  • oxidative stress
  • mitochondrial dysfunction
  • genetic damage

Not coincidentally, these are also key factors promoting cancer. 

In this 2009 study mice with implanted tumors were divided into groups and fed a diet high in numerous fatty acids. The mice fed with linoleic fatty acids demonstrated metastasis–the spread of cancer–four times higher than the rodent groups fed monounsaturated fatty acids like you find in olive oil, and saturated fatty acids prevalent in red meat.

A 2010 study found that mice bed with soybean oil that had been heated in a deep fryer showed four times greater cancer metastasis than mice fed unheated oil.

When we combine the data from these two mouse studies we can infer that deep-fried vegetable oil may cause sixteen times or 1600% greater cancer growth than healthy saturated fats from animal sources. 

Another study showed that tumors formed once rats consumed 20% of their fat in the form of linoleic acid. Recall here that vegetable oils now make up not just 20% of our fat intake, but of our entire caloric intake. 

In line with the studies above, a 2010 study on mice showed that increasing intake of corn oil, but not saturated fats, promoted prostate cancer.

In this same study, the researchers found that not only did vegetable oil increase risk of cancer, a low-fat diet showed no benefits in reducing cancer risk when compared to a diet high in saturated fats (but not PUFAs from vegetable oil). 

For more on why saturated fat is healthy click here.

In the classic Los Angeles Veterans Administration Study, participants were split into two groups. One group increased percentage of total fat intake from vegetable oil. For the control group, there was no change in the type or quantity of fat intake. And both groups consumed the same total amount of fat. 

Alarmingly, but at this point to be expected, the vegetable oil group was 82% more likely to die from cancer. 

Though the groups were randomly assigned, the control (non vegetable oil group) ended up having twice as many heavy smokers. Yet, even with more smokers, this group had significantly fewer deaths from cancer.

graph showing vegetable oil and death from cancer

All-Cause Mortality (Death)

In the major 2013 Sydney Diet-Heart Study, researchers separated study participants into two groups. Like the study above, the total fat intake of both groups was the same. Yet for one group the primary type of fat was linoleic acid from vegetable oil and margarine. The other group got most of their fat from butter, oil, and fatty meat.

Everything else about their diets and lifestyles remained unchanged.

Over seven years of monitoring the vegetable oil group had a 62% greater all-cause mortality rate. 

Of all known risk factors, only morbid obesity and smoking are more likely to kill you than vegetable oils. 

To add more perspective, vegetable oil was shown to be more deadly than a sedentary lifestyle and heavy drinking. 

Furthermore, heavy smoking increases death by 80%. So if increasing vegetable oil consumption to account for 12% of total calories (as the study did) increases the risk of death by 62%, then every 5% increase in calories from vegetable oils is the risk equivalent of smoking 7 cigarettes a day. 

This works out to one daily teaspoon of vegetable oil increasing your risk of death equivalent to smoking 2 cigarettes. 

Is a cigarette or two every once in a while going to kill you? No, and neither is the occasional small amount of vegetable oil. 

Here’s the study abstract:

abstract from study on vegetable oil and all cause mortality

Heart Disease

Another major 2016 randomized control trial known as the Minnesota Coronary Experiment found that the participants who increased their intake of corn oil and margarine had 86% more heart attacks.

Additionally, the study found that participants 65 and older had a higher risk of death after four years.

This was another study conducted to explore the dietary dogma that replacing saturated fat from animal sources like butter, tallow, and fatty meats with vegetable oil would lower cholesterol and therefore reduce the risk of heart disease. 

Interestingly, though the vegetable oil group showed lower cholesterol, they were significantly more likely to die from heart attack.

The study authors conclude: 

conclusion from study on vegetable oils and heart disease

How many people have to die before we can put the anti-saturated fat dogma from the 1960’s out to pasture? It’s high time that we freely eat the healthy pasture-raised animals that our bodies have evolved over millennia to thrive on

graph of vegetable oil and heart attack risk

 In the 2002 MARGARIN Study, 282 participants with multiple heart disease risk factors were randomly selected into two different groups. One group consumed margarine high in linoleic acid from vegetable oil. The other ate margarine high in Omega-3-rich fish oil. 

After two years, the number of strokes, heart attacks, and cardiovascular deaths was 700% higher in the group consuming high linoleic vegetable oil margarine.

graph of study showing increase of risk of heart attack and stroke from consuming vegetable oil

The classic Rose Corn Oil Trial from 1962 looked at the effects of replacing standard dietary fats from meat, dairy, and fish with corn oil. 

Though the trial was relatively small with only 54 participants, the results were dramatic. 92% of the participants from the group consuming corn oil experienced an increase in cardiac events. The corn oil group also suffered a 364% increased risk of death.

These findings from the randomized control trials above are born out in observations comparing omega-6 fatty acid intake from vegetable oils and incidences of heart disease. 

graph comparing countries and rates of vegetable oil consumption and heart attack

Graph comparing vegetable oil consumption with other lifestyle risk factors for mortality

“↑” = “Increased consumption of”; Severe obesity: BMI 35–40 [a]; Heavy smoking: ≥10 cigarettes/day (avg 21.97 or ~1 pack) [b, c]; Vegetable oil: Increase consumption by 12% of calories [d]; Physical inactivity: <2 times/week [e]; Heavy drinking: >14 drinks/week for men or >7 drinks/week for women [f, g, h]; Moderate smoking: <10 cigarettes/day [i] Sugar: ≥73.2g sugar/day for women or ≥79.7g sugar/day for men [j]; ; Air pollution: per 10 μg/m3 long-term exposure to PM 2.5 [n, o]

Observational Studies Correlating Vegetable Oil with Heart Disease

Only randomized control trials like those detailed above can suggest causality. But there have also been a number of well-done observational studies that add correlative data to the argument that vegetable oil is bad for you. 

abstract from study on vegetable oil

In the above study researchers stated “Dietary changes over the past few decades in the intake of n-6 [omega-6] and n-3 PUFA [polyunsaturated fatty acids] show striking increases in the (n-6) to (n-3) ratio (~15 : 1), which are associated with greater metabolism of the n-6 PUFA compared with n-3 PUFA. 

Coinciding with this increase in the ratio of (n-6) : (n-3) PUFA are increases in chronic inflammatory diseases such as nonalcoholic fatty liver disease (NAFLD), cardiovascular disease, obesity, inflammatory bowel disease (IBD), rheumatoid arthritis, and Alzheimer’s disease (AD). By increasing the ratio of (n-3) : (n-6) PUFA in the Western diet, reductions may be achieved in the incidence of these chronic inflammatory diseases.”

abstract from vegetable oil study

From this 2018 study researchers found that high LDL is only a dangerous marker of heart health in the context of a diet high in omega-6. They also discovered that heart attack patients have much more linoleic acid in their arteries than healthy patients. There was also a positive correlation between the severity of heart attacks and arterial plaque buildup from omega-6 fatty acids. 

The researchers concluded, “In summary, numerous lines of evidence show that the omega-6 polyunsaturated fat linoleic acid promotes oxidative stress, oxidized LDL, chronic low-grade inflammation and atherosclerosis, and is likely a major dietary culprit for causing CHD [congenital heart disease], especially when consumed in the form of industrial seed oils commonly referred to as ‘vegetable oils’.”

Depression and Cognitive Disorders

title from study on vegetable oil and depression

In this study using blood samples from 43 participants, researchers found that Six individuals who met the criteria for major depressive disorder had higher omega-6:n-3 ratios and higher levels of numerous inflammatory markers than those who did not meet the criteria.

The authors concluded, “Diets with high n-6:n-3 PUFA ratios may enhance the risk for both depression and inflammatory diseases.”

title of study on vegetable oil and cognition

This 2020 study in mice showed that consuming soybean oil lead to both weight gain and triggered a gene dysregulation that can result in higher rates of neurological disorders including autism, Alzheimer’s disease, anxiety, and depression.

Researchers also found that consuming soybean oil also reduced levels of oxytocin, the hormone responsible for loving bonds. In other words, soybean oil makes destroys our ability to love on the level of neurochemicals. 

Many of the social problems in this country are blamed on a lack of mental health resources. And though it may be true that many people need more psychological help than they have access to, it is equally true that there would likely be far less of a need for mental health resources if we eliminated vegetable oil use on a national level. 

The study authors conclude, “If there’s one message I want people to take away, it’s this: reduce consumption of soybean oil”.

title of study linking canola oil to alzhiemer's

 

From this 2017 study, we see that the negative neurological effects of vegetable oils are not confined to soybean oil. 

In the study, mice fed the human equivalent of 2 tablespoons of canola oil per day showed reduced memory, learning ability, and increased weight gain. 

Researchers described “considerable neuronal damage” and increased formation of beta-amyloid plaques associated with Alzheimer’s disease.

title of study on vegetable oil and neurological disorders

 

In another animal study using baby pigs, researchers found that feeding subjects 1.2% of calories from a PUFA found in vegetable oil lead to healthy brain development. 

But when the percentage was boosted to 10.7% of calories, the PUFA compromised neurodevelopment.

Let’s consider again that Americans consume an average of 20% PUFA from vegetable oil. What’s more, vegetable oil is one of the first ingredients in most baby formulas. 

image of baby formula ingredient label

Source @carnivoreaurelius

title from study looking at vegetable oil and depression

In a study on monkeys fed a “Western diet” that included safflower oil, the most depressed monkeys had the highest blood levels of PUFAs. More PUFA means more depression. See the patten?

picture of depressed monkeys

Vegetable Oil is Bad for Fertility

Considering that vegetable oil interferes with gene signaling and causes inflammation it’s not surprising that it may negatively effect fertility. 

title from study looking at effects of vegetable oil on fertility

A 2020 study looking at the effects of a diet high in vegetable oil PUFA on infant mice demonstrated that a high PUFA diet “during early life caused irreversible metabolic remodeling in testes, with long-term sperm defects…Mechanistically, our data suggests that HFD promotes a pro-inflammatory state in testis, aggravated by a positive feedback system that favors the accumulation of n-6 PUFAs, precursors of inflammatory response signaling molecules.”

Though the authors frame the study in terms of high fat vs. balanced diet, they also found that Saturated fat (SFA) has only a positive effect on fertility and was found to accumulate ONLY in the gonads of fertile animals.”

Though the goal of this study was to test the long-term fertility effects of a high-PUFA diet fed in childhood, there is nothing in the study that prevents the same outcome in adults fed a high-PUFA diet.

Additionally, metabolic science watchdogs Haidut point out, “there is no reason why the findings of this study apply to males only. High-fat (PUFA) diet causes PUFA accumulation just as easily in ovaries as it does in testes. IMO, the epidemic of infertility among Millenials is a corroboration of that hypothesis. The majority of that generation was almost entirely formula-fed and baby formula has a PUFA composition that is even worse than the high-fat diet in this experiment.”

 

diagram showing effects of vegetable oil on sperm health

 

So, if PUFA-loaded formula is best avoided, and you’re introducing your child to solid food, what should infants eat?

Dentist and Carnivore diet thought leader Kevin Stock observed “that what kids eat today is incongruent with oral health. Most have cavities. Most have underdeveloped jaws (maxilla and mandibles), crowded teeth, and compromised breathing patterns.”

Stock cites a recent paper published on new evidence-based dietary guidelines for feeding infants from birth to 24 months old.

Guess what it recommends? Yep, meat!

Weight Gain

Carrying fat on our bodies isn’t a bad thing, in fact, it’s the way we’ve evolved to store energy for leaner times. 

But since PUFAs are unstable, oxidative, and inflammatory having too much fat made from PUFA lipids is a key factor in numerous diseases. 

Studies show that PUFA accumulates as body fat very quickly. 

study title on vegetable oil and weight gain

In this study on rats, two groups received diets with identical macronutrient ratios of fat, protein, carbs, and calories. They differed only in the source of the fats. 

The group of rats that got their fat from safflower oil showed a 12.3% increase in total body weight compared to the rats eating traditional fats.

graph showing vegetable oil and weight gain

study title of vegetable oil and weight gain

In this study, rabbits were divided into three groups. Each group was fed the same foods, the only difference was how much heat the vegetable oil had been subjected to. 

The first group received unheated vegetable oil. The vegetable oil of the second group was heated once. The third group got vegetable oil that had been repeatedly heated. 

graph showing weight gain from heated vegetable oil

The group consuming the vegetable oil heated only once gained 6% more body weight than the group that consumed unheated vegetable oil. 

The group that ate the repeatedly heated oil gained an incredible 45% more weight.

Though this was an animal study it is food for thought when considering ordering food fried in a deep fryer. 

Is Vegetable Oil Bad for You? The Bottomline

When considering both randomized control trials using humans and animals, historical evidence, and large-scale observational studies, the totality of evidence suggests that yes, vegetable oil is bad for you. 

Vegetable oil has been shown to cause inflammation and disrupt hormone signaling in ways that lead to increased risk of: 

  • Cancer
  • All-cause mortality
  • Heart disease
  • Depression
  • Neurodegenerative disorders including Alzheimer’s, dementia, and Parkinson’s disease
  • Impaired fertility
  • obesity

It is likely that there are numerous factors in modern society that contribute to the rise of inflammatory diseases that kill the most people across the globe. However, from the available data regarding lifestyle choices influencing mortality rates, only morbid obesity and heavy smoking are more deadly than vegetable oil consumption.

 

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