Soybean oil is the most consumed vegetable oil in the United States. Mostly because many people still believe there are health benefits to cooking with soy (Glycine max).
But it’s also popular because it’s a cheap, mass-produced oil that manufacturers can use in packaged, processed foods. It’s even used to produce biodiesel.
From GMO soybeans to harmful hydrogenation, you’re about to get all the science-based details behind the health effects of this popular ingredient and why it’s one of the worst oils on the planet for your health.
What Is Soybean Oil?
Soybean oil is made from pressing the oil from soybeans, much like you’d make oils from any seed. And like other seed oils, it’s high in unstable polyunsaturated fatty acids (PUFAs).
The fatty acid composition of soybean oil (per 100g) is roughly:
- 58g polyunsaturated fat (mostly linoleic and linolenic acid)
- 23g monounsaturated fat
- 16g saturated fat (such as palmitic and stearic acids)
Soy oil is particularly high in an omega-6 fatty acid called linoleic acid, a bad fat that’s easily damaged by heat.
As you can see, this oil is relatively low in saturated fat, which is probably why so many Americans have gravitated toward it as a “healthy” cooking oil over the years.
According to the USDA, processed soybeans are the second largest source of vegetable oil — right behind palm oil — as well as the main source of protein for animal feed[*]. It comes as no surprise that Americans are the second biggest consumers of soybean oil in the world, preceded only by the Chinese[*].
For context, over 60% of U.S. vegetable oil consumption is soybean oil, which is linked to obesity and other health conditions[*]. It’s in salad dressings, soybean meal, snacks, and margarine. And most of these products contain GMO soy.
However, we now know that oils high in saturated fats such as palm oil are in fact healthy, and have never been directly related to heart disease. As it turns out, they’re much better for you than unstable PUFA oils — especially when it comes to cooking.
Soybean oil isn’t just highly unstable and easily oxidized — soy products are notoriously allergenic, hard on your digestive system, and one of the most hydrogenated oils out there.
GMO soy is a whole other nightmare, and you should avoid it at all costs. It doesn’t matter if it’s GMO, organic, or even high oleic. It’s the high levels of linoleic acid that makes this one of the worst edible oils for your health.
Linoleic Acid: The Bad Fat
Polyunsaturated fat isn’t bad for you. In fact, two kinds of PUFAs — omega-3 and omega-6 fatty acids — are considered essential fatty acids and play an important role in your overall health.
But certain types of polyunsaturated fats are highly unstable, easily oxidized, and pro-inflammatory.
Linoleic acid is one of those. And soybean oil is about half linoleic acid.
High linoleic acid oils are bad news even when you consume them at room temperature. But they’re even worse for you when they’re heated.
When you expose high-linoleic soybean oil to high temperatures, you generate oxidized lipids. These oxidized lipids increase inflammation in your bloodstream, increasing your risk of atherosclerosis (hardening of your arteries) and heart disease[*].
High linoleic acid oils also throw your omega-6 to omega-3 ratio out of whack. A healthy ratio is at least 4:1, but many health experts argue that a 1:1 ratio or more in favor of omega-3s is ideal.
Unfortunately, most Americans consume super high levels of omega-6s — more like a 1:12 or 1:25 ratio in favor of omega-6s. And high omega-6 levels increase your risk of obesity, inflammation, and deteriorate brain health[*][[*].
Another way that linoleic acid is linked to obesity? By boosting arachidonic acid — another omega-6 fat that can contribute to obesity[*].
Soybean Oil Side Effects
It may seem innocent, but chronic consumption of this oil might cause some severe health problems. Most common? Obesity. But that’s certainly not the end of the list.
#1: Diabetes
Type 2 diabetes is the result of chronically-high blood glucose levels, followed by insulin resistance or impaired insulin secretion. Approximately 90% of people with Type 2 diabetes are overweight or obese.
That makes obesity an important factor in Type 2 diabetes development.
For instance, gaining lots of fat is a sure sign of insulin dysfunction. And when insulin stops working, your blood sugar stays elevated, increasing your risk of chronic disease[*].
And high linoleic diets are linked to obesity, as we covered above.
In one rodent study, for instance, mice were given either coconut oil or coconut oil plus soybean oil. When the data was collected, the mice fed soybean oil had more insulin resistance, were more obese, and had higher blood sugar than mice fed coconut oil, all of which are risk factors for diabetes[*].
#2: Liver Disease
Your liver works hard to regulate your cholesterol levels, detoxify your blood, aid in digestion, process nutrients, and the list goes on[*].
But one of the leading causes of liver dysfunction in the U.S. is on the rise. It’s called non-alcoholic fatty liver disease (NAFLD) and it currently affects 30-40% of Americans[*].
This accumulation of visceral liver fat comes with a host of symptoms and complications, including:
- Fatigue
- Abdominal pain
- Abdominal swelling
- Jaundice
And the crazy part is that NAFLD is entirely preventable.
One of the leading causes of NAFLD is, of course, obesity. And obesity is made more prevalent by the consumption of high-carb processed foods and omega-6 fats.
Soybean oil, in particular, seems to contribute to NAFLD.
The results from the same rodent study suggest that mice with the high soybean oil diet were much more prone to metabolic disease, including fatty liver[*].
#3: Heart Disease
Again, obesity increases heart disease risk[*], so by definition anything that contributes to obesity will increase your risk of cardiovascular disease.
Yet when it comes to your heart, soybean oil can do more than just make you fat. It can also cause:
- Lipid Peroxidation: Oxidized lipids, generated from cooking PUFAs like soybean oil, contribute to atherosclerosis, aka hardened arteries, aka heart disease[*]
- High O-6 Consumption: High omega-6 consumption increases inflammation — a key CVD risk factor[*]
- Lower HDL: A high soybean oil diet lowers HDL cholesterol (the “good” cholesterol), which may indicate decreased cholesterol transport[*]
Partially hydrogenated soybean oil (PHSO) is even worse. PHSO is a trans fat, a fat you can’t find in nature that’s strongly linked to metabolic disorders and heart disease[*].
In mice, PHSO diets raise levels of a particle called Lp(a) — pronounced L P little a[*].
You might not have heard of it, but Lp(a) is the most dangerous lipid out there. Researchers have shown that, in humans, elevated Lp(a) causes cardiovascular disease[*].
Clearly, this isn’t the heart-healthy oil the Food and Drug Administration (FDA) makes it out to be.
#4: Immune Toxicity
Soybean oil may be toxic to critical immune cells[*].
In one study, researchers gave participants either olive oil or soybean oil for two weeks, then measured lymphocyte and neutrophil levels.
Unlike olive oil, soybean oil was toxic to both types of immune cells — immune cells that you need to fight infections and keep you feeling strong.
“Soybean oil emulsion given as a single dose of 500 mL,” concluded the scientists, “promotes lymphocyte and neutrophil death that may enhance the susceptibility of the patients to infections.”
How to Choose the Healthiest Oils
Soybean oil consumption is linked to obesity, fatty liver, heart disease, and metabolic syndrome.
So how do you choose a healthy fat, especially when it comes to cooking?
Use this guide to choose the best oil for you.
#1: Choose High-Heat Cooking Oils
Oils from soybeans, canola, peanut, and sunflower are all examples of high omega-6 fats that cause inflammation and cellular damage. Avoid these oils whenever you can.
Instead, choose a more stable cooking oil like palm oil, butter, or avocado oil. These fats hold up to high heat and have high smoke points — even high enough for frying.
Plus, they’ll make your veggies taste better.
#2: Read Labels
Most packaged foods contain hidden and cleverly-named ingredients that sound natural but are actually terrible for you. Soybean oil is one of those ingredients. Again — sounds innocent, but it’s highly processed, easily oxidized, and contributes to fat gain and other health issues.
Packaged foods in general also tend to be higher in sugar, carbs, trans fats, vegetable oils, and artificial ingredients.
Make sure you’re getting the highest-quality food possible and avoid ingredients like:
- Soybean oil
- Canola oil
- Safflower oil
- Sunflower oil
- Anything with the word hydrogenated
- Anything that says trans fats
#3: Eat More Omega-3 Fatty Acids
Remember the optimal O-6:O-3 ratio? Right, 1:1. Or better yet, 10:1 in favor of omega-3s.
That means eating more omega-3s and cooling it on the omega-6s.
Foods rich in omega-3s include:
- Salmon
- Fish eggs
- Cod liver oil
- Grass-fed beef
- Other cold-water (wild-caught) fish
#4: Choose Your Keto Fats Wisely
If you’re on a ketogenic diet, most of your calories come from fat. At least 60%[*].
This means you need to choose healthy fats like:
- Saturated fats — palm oil, coconut oil, grass-fed butter, and MCT oil
- Monounsaturated fats — macadamia nuts, olive oil, and avocados
- Polyunsaturated fats — nut butter, fish, fish eggs, and egg yolks
You also need to shun unhealthy fats like:
- High omega-6 vegetable oils — soybean, canola, safflower, and sunflower
- Trans fats and hydrogenated fats
Get these tips handled and you’re on your way to fat-fueled health.
Steer Clear of Oil From Soybeans
Fat is essential for your body to create critical hormones and neurotransmitters. Your body also loves running off of ketones from fat — a more efficient form of energy than glucose.
But choosing the right dietary fats can be tough — especially if you’re just starting out on the keto diet.
One thing’s for sure — steer clear of soybean oil in any form. It’s highly unstable (has a low shelf life), oxidizes easily, and is related to obesity, diabetes, heart disease, and fatty liver[*].
Instead, give your body what it wants — stable, nutritious, keto-friendly fats. The truth is: they taste much better than oil from soybeans anyway.
Learn more about which oils are best to add to your keto diet by reading these helpful guides:
Should You Use Sunflower Oil? The Benefits and Risks
Is Corn Oil Healthy? What the Science Says
Is Vegetable Oil Bad For You? The Top 7 Vegetable Oils to Avoid