Soybean Oil

What it is

Soybean oil is high in linoleic acid, an omega-6 polyunsaturated fatty acid. Linoleic acid is essential, meaning our bodies need some from food—but soybean oil is certainly not the only way to get it.

Omega-6 fats are naturally found in whole foods such as walnuts, sunflower seeds, pumpkin seeds, eggs, and other nuts and seeds, which also provide protein, fiber, vitamins, minerals, and other nutrients.

The controversy isn't about whether we need omega-6 fats—we do. The questions are more about how much we consume, the foods we're getting it from, how oils are processed, and what happens to polyunsaturated fats when they're exposed to heat and oxidation.

Why it is used

Why Is It Used?

Soybean oil is widely used because it is:
inexpensive
mild in flavor
widely available
easy to use in large-scale food production
useful for frying, sauces, dressings, baking, and packaged foods

Its widespread use has made it easy to consume regularly without intentionally choosing it.

Where it is commonly found

Where Is It Commonly Found?

Soybean oil is commonly found in:
Mayonnaise
Salad dressings
Sauces and dips
Chips and crackers
Restaurant fried foods
Fast food
Frozen meals
Packaged snacks
Baked goods
Breads and tortillas
Margarine and spreads
Some processed meats

A significant amount of soybean oil in the modern diet comes from restaurant and ultra-processed foods rather than soybean oil used for home cooking.

What current research says

Research on soybean oil is more mixed than either side of the debate often makes it sound.

One of the biggest concerns is oxidation. Soybean oil is high in polyunsaturated fats, which are chemically more vulnerable to breaking down when exposed to heat and oxygen. This becomes especially important when oil is heated for long periods or reused for frying. Studies have found that repeatedly heated soybean oil develops increasing levels of oxidation and breakdown products.

Some of those breakdown products, including reactive aldehydes such as 4-HNE and malondialdehyde (MDA), can interact with cells, proteins, and DNA. Laboratory and animal research has linked these compounds with oxidative stress, inflammation, and tissue damage. This doesn't mean eating soybean oil automatically causes these effects—the amount of oxidation depends greatly on how the oil is stored, heated, and reused.

There are also some concerning animal studies involving soybean oil itself. A 2024 mouse study found that a high-fat diet containing soybean oil caused greater neuroinflammatory changes than a high-fat diet containing lard, including changes involving the gut-brain axis, gut bacteria, and immune cells in the brain. Other mouse studies have associated high-soybean-oil diets with greater weight gain, fatty liver, insulin resistance, changes in metabolic signaling, and altered gene expression in the hypothalamus.

These findings are worth taking seriously enough to investigate further, but animal studies cannot tell us that the same effects occur in humans.

The evidence around omega-6 and inflammation is also important. Soybean oil contains a large amount of linoleic acid, an omega-6 fatty acid. Although omega-6 fats can be involved in inflammatory pathways in the body, controlled human studies generally have not found that increasing linoleic acid increases common blood markers of inflammation.

So the current evidence doesn't support the simple claim that “soybean oil = inflammation.” At the same time, it also doesn't erase legitimate questions about oxidation, repeatedly heated oils, very high long-term intake, or the concerning effects seen in experimental research.

What we know: soybean oil's polyunsaturated fats can oxidize, particularly during prolonged or repeated high-heat cooking, and some of the compounds created through oxidation can have harmful biological effects.

What we don't know yet: whether the amount of soybean oil typically consumed by humans—particularly over many years—causes the same metabolic, inflammatory, or neurological effects seen in some animal studies.

That's why we choose to avoid soybean oil when practical while remaining honest that some of the concerns still need stronger human evidence.

Potential concerns or controversies

Oxidation
Soybean oil is high in polyunsaturated fats, which are more vulnerable to oxidation than more saturated fats and many oils higher in monounsaturated fat. Heat, oxygen, light, and time can accelerate this process.

Repeated High-Heat Cooking
Repeatedly heating soybean oil—such as reusing oil in a deep fryer—can increase its breakdown and the formation of oxidation products. This is one reason we are particularly cautious about soybean oil in fried restaurant foods.

Potentially Harmful Oxidation Products
As polyunsaturated fats oxidize, they can form reactive compounds such as 4-HNE and malondialdehyde (MDA). Laboratory and animal research suggests these compounds can contribute to oxidative stress, inflammatory signaling, and cellular damage. How much this translates to harm from normal human dietary exposure is less clear.

Inflammation Debate
Soybean oil is often described as inflammatory because it is high in the omega-6 fat linoleic acid. There are biological reasons this concern has been proposed, but controlled human studies generally have not shown that increasing linoleic acid raises common inflammatory markers.

Metabolic & Brain Effects in Animal Research
Some mouse studies have associated high-soybean-oil diets with obesity, insulin resistance, fatty liver, altered brain gene expression, and neuroinflammatory changes. These findings raise legitimate questions for further research, but they have not established that the same effects occur in humans.

How Much We're Consuming
Soybean oil is now extremely common in packaged and restaurant foods, making it easy to consume frequently without realizing it. Researchers continue to investigate whether high, long-term exposure has effects that shorter human studies may not capture.

Highly Refined
Most conventional soybean oil goes through extensive refining to produce a neutral, shelf-stable oil.

Important context: These concerns don't mean soybean oil has been proven toxic. Some concerns—particularly oxidation during repeated heating—have strong chemical and experimental support, while others, such as long-term metabolic or neurological effects, still rely heavily on animal or mechanistic research. That's why we choose to avoid soybean oil while being careful not to claim more than the evidence currently shows.

Practical takeaway

We choose to avoid soybean oil as much as reasonably possible, particularly in fried and highly processed foods.

We avoid it because it is usually highly refined, is extremely easy to consume in large amounts, its polyunsaturated fats are relatively susceptible to oxidation, and animal and mechanistic research raises questions that we believe deserve further long-term human study.

At home, we generally prefer extra-virgin olive oil, avocado oil, butter, tallow, or ghee, depending on what we're making.

When we have the choice, we always choose alternatives.

Alternative or common names

• Soy oil/Soya oil
• Soyabean oil
• Vegetable oil