Soybean oil is in almost all fast food and ultra-processed packaged foods.
Unfortunately, it is not a healthy option.
Since it is so high in easily oxidizable omega-6, it’s a poor cooking oil choice.
This article takes a look at eight harmful effects of soybean oil backed by scientific research.
1. Soybean Oil is Obesogenic and Diabetogenic
Look around, and it’s clear to see that Western society has an obesity problem.
For instance, 2 out of every 3 adults in the United States (68.8%) are either overweight or obese (1).
Some people lay the blame for this on red meat and animal fat, which is total nonsense;
As you can see, the consumption of red meat has actually fallen over the past several decades while leaner poultry increases in popularity.
However, if we are looking for a possible dietary villain, then soybean oil consumption has grown by a huge magnitude.
It is in almost everything we eat; not only as a cooking oil but also in salad dressings and processed foods.
And studies show that it is “more obesogenic and diabetogenic than fructose” (2).
The (Waist) Expanding Role of Soybean Oil in Obesity
Vegetable oils were almost unheard of in the early 20th century. In contrast, they are everywhere these days.
Specifically, domestic consumption of soybean oil has more than quadrupled from 1,652,000 tons in 1964 to 6,576,000 tons as of 2016 (3).
At the same time, there has been an explosion in obesity and diabetes. And here are some possible reasons as to why;
- An animal study compared the impact of a diet high in soybean oil to high fructose and coconut oil diets. The mice fed large amounts of soybean oil had significantly more weight gain, diabetes, and insulin resistance. Additionally, the soybean oil diet upregulated cancer, inflammation and obesity-related genes (2).
- Another animal study fed mice a high-fat diet of either soybean, olive oil, MCT oil, peanut oil, or tea oil. Following the study, body weight and body fat were significantly higher in the soybean oil group compared to all others. Also, the soybean oil group had visible fatty liver disease—the MCT, olive oil, and tea oil mice did not (4).
- In a study comparing butter and soybean oil, fat oxidation increased in the group fed butter. In the soybean fed group, subjects showed an inability to oxidize fat while resting (5).
2. Soybean Oil Leads to Inflammation
The chart below shows the nutrition facts per one tablespoon of soybean oil (1);
|Vitamin E||6% RDA|
|Vitamin K||31% RDA|
As shown above, soybean oil is predominantly a source of polyunsaturated fats (PUFA).
The omega 6 to 3 ratio is approximately 7.4: 1.
When you consider that soybean oil is in almost everything, it’s not hard to imagine someone having 4 or 5 tablespoons per day.
In other words, about 30 grams of omega-6 and only 4 grams of omega-3. A huge difference.
Importance of Balancing Omega-6 and 3
Although both omega-3 and omega-6 are essential fatty acids, we should consume them in relative balance.
Research shows that ancestral diets were approaching a 1:1 ratio (6).
Due to the excessive amount of vegetable oils in the modern diet, people are eating way too much omega-6 and nowhere near enough omega-3.
Notably, estimates place the modern diet as having a ratio of 20:1 or higher (6).
Omega-6: Healthy Until It’s Not
Omega-6 is an important fatty acid that is pro-inflammatory in nature, and this is a good thing.
For instance, some inflammation in the body is necessary for healing cuts and wounds.
However, in excessive amounts it causes our body to stay in an inflammatory state — and chronic inflammation is a known risk for the majority of illnesses (7).
Some harmful effects of too much omega-6:
- As omega-6 competes with omega-3 for uptake into our cells, too much omega-6 means a deficiency of anti-inflammatory omega-3 (8).
- Studies show that a lower dietary omega-6 to omega-3 ratio reduces inflammation and mortality risk from heart disease (9).
- Chronic diseases such as diabetes, obesity, IBD and arthritis all have associations with increased omega-6. Imbalances in the omega 6 to 3 ratio have likely increased the prevalence of multiple inflammatory, disease-causing processes (10).
That said, this is not a problem unique to soybean oil. Other oils rich in polyunsaturated fats such as grapeseed oil have the same problems.
3. Soybean Oil Can Increase the Risk of Cardiovascular Disease
Despite the food industry’s message that soybean oil is ‘heart healthy,’ most people with interest in nutrition know better.
In fact, the science shows it is probably the very opposite; soybean oil is unhealthy and likely damages the heart;
- Compared to saturated fats, soybean oil is very unstable as it is predominantly a polyunsaturated fat. Vegetable oils are susceptible to oxidation when exposed to heat, which can cause their fats to oxidize. Consuming oxidized fats has a detrimental impact on blood pressure and cholesterol and also increases inflammation (11).
- An unbalanced over-production of omega-6 in the body has a strong association with atherosclerotic diseases (cardiovascular disease) (12).
- ‘Heart healthy’ vegetable oils possess an “undesirable PUFA content.” Current data suggests that switching to traditional fats like ghee and coconut oil “would reduce the risk of heart disease” (13).
And this is just a small drop in a large ocean of negative studies. Have a search for yourself and discover the ‘heart healthy’ myth.
4. Soybean Oil is Manufactured Using Harsh Chemical Solvents
Do you know how to make olive or avocado oil?
It is a natural process that uses a cold-press to squeeze the oil out of the fruit and then bottle it.
In contrast, it is tough to squeeze oil out of seed oils, and so the soybean oil production process uses;
- Extreme heat
- Chemical solvents
Here is a diagram explaining the manufacturing process;
As you can see, producing soybean oil is far from ‘natural’ and involves an enormous amount of chemical refining.
The soybean oil is;
- Bleached to look edible
- Extracted with harsh chemical solvents like hexane, a recognized neurotoxin (14)
- Deodorized to hide the terrible smell
However, this process isn’t unique to only soybean oil, and other processed vegetable oils such as Canola oil also use it.
Does Soybean Oil in Stores Contain These Chemicals?
Maybe, maybe not.
Firstly, the manufacturers claim the finished product doesn’t contain any appreciable amount of these chemicals (because the oil is “cleaned” and “refined”).
Despite this, studies show that residual amounts usually remain in the finished oil. Based on equivalent-dose animal studies, these amounts are apparently safe (15).
However, independent tests have investigated the issue and show that hexane residues “10 times higher than what the FDA considers normal” appear in soy products (16).
No FDA regulation requires testing vegetable oils for hexane contamination.
5. Soybean Oil Changes the Fatty Acid Composition of our Cells
The above graph shows the explosion in the consumption of polyunsaturated fat over the past century.
As soybean oil is the most significant source of omega-6 in the US, it is a major part of this trend.
Too Much Polyunsaturated Fat is Dangerous
Polyunsaturated fats are missing many hydrogen atoms; as a result, their carbon atoms are very fragile and susceptible to oxidization.
The first thing to remember here is that our cells and tissues predominantly contain saturated and monounsaturated fat.
For one thing, this makes the fat in our cells stable. Just like vegetable oils can oxidize due to air, light, or heat exposure, so can fats inside our body.
Therefore, if we are consuming large amounts of omega-6 through vegetable oil, this polyunsaturated fat slowly changes the fatty acid composition of our cells.
Once our cells incorporate a higher amount of polyunsaturated omega-6, they become less stable and more prone to the effects of oxidation;
- Omega-6 is a “melanoma stimulator” because it makes our skin cells susceptible to damage from UV rays (17).
- An animal study separated mice into different groups and fed them varying amounts of dietary omega-6 PUFA. The higher their dietary intake, the more they developed cancerous tumors (18).
6. Unfermented Soy Might Be Harmful
Not only does soybean oil have harmful effects but so do the broader range of soy-based foods.
Whether soy is healthy or not is a persistent topic of discussion, with various studies showing harm and others showing positive health effects.
However, not all soy is the same and fermented soy—like Japanese staples miso and natto—is an entirely different category compared to processed soy products.
Some reasons we should proceed with caution on soy include;
- Soy mimics the effects of estrogen—the female hormone—in the body (19).
- Infants fed soy have circulating phytoestrogens 13,000-22,000 times higher than natural estrogen levels; at this time, the long-term reproductive effects are unclear. Additionally, adult males consuming soy products may experience fertility issues (20, 21).
- Existing data for the health benefits of soy is “inadequate and inconsistent,” and there is concern that widely consuming soy products may cause harm to the public (22, 23, 24).
7. Heated Soybean Oil is Likely Carcinogenic
Due to the unstable composition of soybean oil, exposing it to heat is a terrible idea. In contrast to saturated fats, omega-6 vegetable oils are very prone to oxidation.
However, the problem is that restaurants and fast food chains around the world even use soybean oil for deep drying. Using soybean oil at high heat virtually guarantees a large dose of oxidized fats (25).
Studies on Heating Oils and Carcinogens
- Trans fats, toxic aldehydes, and various other “volatile compounds’ form when frying soybean oil at high heat (26, 27).
- Heat degrades omega-6 vegetable oils into toxic compounds that have “properties that often signal carcinogenesis” (28).
- One study fed female rats either soybean oil or ghee; the soybean oil group had higher tumor incidence, larger tumor size, and a more rapid onset of cancer (29).
- In animal studies, soy oils oxidized through heating cause oxidative stress and also increase the blood pressure in subjects (30).
8. Made From GMO, Glyphosate-Sprayed Soybeans
The industrial giant Monsanto’s glyphosate is one of the most controversial topics in the health world.
It is a chemical pesticide which the world health organization label as “probably carcinogenic to humans.” Glyphosate has links to a variety of modern, chronic diseases including cancer and neurological diseases (31, 32, 33, 34).
Over 90% of soybeans are genetically modified (GMO) for resistance to glyphosate. This modification allows the plant to survive being sprayed with pesticides and herbicides (35).
A recent study investigated the composition of natural soybeans versus GMO soybeans treated with glyphosate. The results showed that (36);
- The soybeans not treated with glyphosate all had better nutritional profiles than the GMO beans.
- Glyphosate-sprayed soybeans contain residual amounts of the chemical.
GMO soybeans are responsible for the vast majority of soybean oil. Many people have a concern that these scientifically modified beans may damage health.
Overall, the evidence is clear that soybean oil poses numerous dangers to our health.
On the positive side, there is no reason whatsoever to use this highly processed oil as there are many better alternatives.
If you are looking for a substitute for soybean oil, then it is better to use fat based around saturated and monounsaturated fats.
Animal fats such as lard, butter, and ghee are all perfectly healthy.
Fruit oils such as avocado, coconut and olive oil are also a good choice.