Does Soybean Oil Cause Inflammation? Here’s What to Know

Soybean oil is everywhere. It is in salad dressings, mayonnaise, crackers, and fried foods at most restaurants. And yes, research shows that some types of soybean oil can promote inflammation in the body. But not all soybean oil is the same, and the real story depends on how the oil is made and what else you are eating. Here is what the science actually says about soybean oil and inflammation, without the hype.

What is soybean oil and why do people think it causes inflammation?

Soybean oil is a vegetable oil pressed from soybeans. It became popular in the 1900s because it is cheap to produce and has a neutral taste. Today it is the most widely consumed cooking oil in the United States. The average American eats about 65 pounds of soybean oil per year, mostly from processed foods.

The concern about inflammation comes from the type of fats in soybean oil. It is high in omega-6 fatty acids, specifically linoleic acid. The body needs omega-6s, but the modern diet has too many of them relative to omega-3s. A ratio of omega-6 to omega-3 that is too high is linked to chronic inflammation. Some researchers believe this imbalance is a driving factor behind diseases like heart disease, arthritis, and metabolic syndrome.

But the omega-6 theory is not the whole story. Some studies have found that linoleic acid itself does not cause inflammation in healthy people. The problem may be more about the processing and the context of the diet.

Does soybean oil cause inflammation in the human body?

The short answer is that it depends on the person and the dose. Research published in the journal Lipids found that replacing saturated fats with soybean oil lowered cholesterol but did not increase inflammatory markers in most people. In fact, some studies show that linoleic acid can reduce inflammation when it replaces saturated fat.

However, a 2020 study from the University of California, Riverside found something different. When mice ate a diet high in soybean oil, they developed obesity, diabetes, and insulin resistance. The researchers also saw changes in the brain that affected mood and anxiety. The study pointed to a compound called stigmasterol, not the omega-6 fat, as a possible cause. This is a new finding and has not been confirmed in humans yet.

Human studies are mixed. Some show that high intake of soybean oil raises markers like C-reactive protein (CRP), which signals inflammation. Others show no effect. The difference may come down to whether the oil is fresh or reused, how much you eat, and what else is in your diet. If you eat soybean oil with a lot of sugar and refined carbs, the combination is likely worse than the oil alone.

What does the research on soybean oil and inflammation actually show?

Let us look at the strongest evidence. A 2017 review in the Journal of the American College of Nutrition looked at dozens of studies on omega-6 fats and inflammation. The authors concluded that linoleic acid does not raise inflammatory markers in healthy adults. They also noted that people who eat more linoleic acid tend to have lower rates of heart disease.

But here is where things get complicated. Most of those studies used fresh soybean oil. In real life, soybean oil is often heated to high temperatures and reused multiple times in restaurants and food manufacturing. When soybean oil is heated repeatedly, it forms compounds called lipid oxidation products. These compounds are known to cause inflammation and damage cells. A 2019 study in Food Chemistry found that repeatedly heated soybean oil increased inflammatory markers in rats.

Another issue is that soybean oil is often hydrogenated to make it solid for margarine and shortening. Hydrogenation creates trans fats, which are strongly linked to inflammation and heart disease. The FDA banned artificial trans fats in 2018, but small amounts can still be found in some processed foods. If you are eating old margarine or baked goods made before the ban, you are likely getting trans fats from soybean oil.

How does soybean oil compare to other cooking oils for inflammation?

Not all oils affect the body the same way. Here is a quick comparison of common cooking oils based on their fatty acid profiles and how they affect inflammation.

The key takeaway is that soybean oil has a high omega-6 ratio, but that alone does not guarantee inflammation. Olive oil and avocado oil are better choices because they contain antioxidants and are more stable at high heat. Canola oil has a better omega-6 to omega-3 ratio and is less processed in many cases.

What are the practical effects of cutting soybean oil from your diet?

Some people report less joint pain, clearer skin, and better digestion when they stop eating soybean oil. These reports are real, but they are not proof that soybean oil is the cause. When you cut out soybean oil, you also cut out fried foods, processed snacks, and many fast-food meals. Those foods are inflammatory for many reasons beyond the oil itself.

A 2021 study in Nutrients found that people who replaced vegetable oils with olive oil or avocado oil had lower levels of inflammatory markers after 12 weeks. But the study also asked participants to eat more vegetables and fish. The diet change as a whole likely mattered more than the oil swap alone.

If you want to test whether soybean oil affects you personally, try removing it for three weeks. Use olive oil, avocado oil, or butter instead. Keep a journal of how you feel. If your symptoms improve, you have your answer. If nothing changes, soybean oil may not be a problem for you.

One non-obvious point: soybean oil is in many foods you would not expect. It is in canned soups, salad dressings, protein bars, coffee creamers, and even some dark chocolates. Reading labels is the only way to know for sure if you are eating it.

Common misconceptions about soybean oil and inflammation

Misconception 1: All omega-6 fats are bad. This is not true. Linoleic acid, the main omega-6 in soybean oil, is an essential fat. Your body cannot make it. The problem is not omega-6 itself but the ratio of omega-6 to omega-3 in the diet. Most Americans eat 15 to 20 times more omega-6 than omega-3. The ideal ratio is closer to 4 to 1 or lower.

Misconception 2: Soybean oil is the same as soy protein. They are completely different. Soybean oil is a fat. Soy protein is the protein part of the bean. People with soy allergies react to the protein, not the oil. Highly refined soybean oil is considered safe for most people with soy allergies because the protein is removed during processing.

Misconception 3: Cutting out soybean oil will cure inflammation. This is widely claimed but strong evidence is limited. Inflammation is complex. It involves diet, stress, sleep, exercise, gut health, and genetics. Removing one oil from your diet may help, but it is not a cure. Managing inflammation usually requires multiple changes over time.

Misconception 4: Organic soybean oil is safe. Organic soybean oil still has a high omega-6 ratio and can still form harmful compounds when heated. Organic does not mean anti-inflammatory. It means no pesticides were used. The health effects of the oil itself remain the same.

What to avoid if you are concerned about soybean oil

If you want to reduce your exposure to soybean oil, focus on these foods first. They are the biggest sources in the American diet.

• Fast food fried items like french fries, chicken nuggets, and onion rings. Most fast-food chains fry in soybean oil.
• Packaged snacks like crackers, chips, and microwave popcorn. Check the label — soybean oil is often the first or second ingredient.
• Salad dressings and mayonnaise. Most commercial brands use soybean oil as the base. Look for brands that use olive or avocado oil.
• Margarine and vegetable shortening. These are made from hydrogenated soybean oil. Butter or coconut oil are better alternatives.
• Protein bars and meal replacement shakes. Many contain soybean oil to add fat and texture. Read the ingredient list carefully.

One more thing to watch for: soybean oil is often labeled as “vegetable oil” in restaurants and on food packages. If a product says “vegetable oil” and does not list the specific oil, it is almost certainly soybean oil. Canola oil and palm oil are sometimes used, but soybean oil is the default because it is the cheapest.