What Are Seed Oils? Are They Actually That Bad? Here’s What Science Says

Despite the controversy, seed oils can be a fine addition to a balanced diet. 

If you spend time on social media, you have probably seen influencers warning about the dangers of seed oils, often sharing a list of seed oils to avoid and claiming they contribute to inflammation and chronic disease. However, experts argue that these oils can be part of a balanced diet.

So, what is the truth? Are seed oils something to eliminate, or can they be consumed without harm? We explored the research to find out whether seed oils are bad for your health. But first, what exactly are seed oils?

What are seed oils?

As per UCHealth Today, seed oils are cooking oil named after the plant, vegetable, seed, or nut from which it is derived. Often called vegetable oil, seed oils range in color from light golden to deep amber, with flavors from neutral to rich. 

Their versatility makes them essential for cooking, baking, and food production. For example, sesame oil has a strong taste and is ideal for dressings and marinades, while milder oils like peanut or canola can be used for baking or grilling.

However, seed oils are criticized for their processing and health effects. Among these, the ‘hateful eight’ vegetable seed oils include:

Seed oils are generally extracted from the plants using either chemicals or mechanical methods. Critics argue that chemical extraction leaves harmful residues like hexane. 

While hexane is harmful as a gas, it is used as a liquid to extract oil, which then evaporates, and studies show no evidence that trace amounts in food pose a health risk.

Moreover, seed oils can be extracted by cold or expeller pressing without chemical solvents. In fact, these oils became more common in the human diet after the mechanical screw press was invented in 1888.

Seed oil vs olive oil vs vegetable oil

As mentioned earlier, seed oil refers to oils extracted from plants, vegetables, seeds, or nuts. Most of these oils undergo a refining process, which includes bleaching and deodorizing. 

Olive oil, on the other hand, is a vegetable oil but not a seed oil, as it is extracted from the fruit of the olive tree. It is generally less processed, especially extra virgin olive oil, and retains more of its natural antioxidants and healthy fats.

Meanwhile, vegetable oil is a broad term that can refer to any oil derived from plants, including both seed oils and olive oil.

Seed oil nutrition

Since seed oil comes from the seeds of plants such as sunflower, soybean, canola, flaxseed, and sesame, its nutrition also depends on the type of oil used.

For example, sunflower oil is high in vitamin E and is primarily composed of unsaturated fats, including linoleic acid (omega-6) and oleic acid (omega-9). Canola oil, recognized as a “healthy” oil, is low in saturated fat (7%) and high in omega-3 (9-11%). 

PBS reported that from 1909 to 1999, U.S. seed oil consumption, specifically soybean oil, grew 1,000 times, and in the past 50 years, increased seed oil intake has raised omega-6 levels in Americans’ body fat by 136%.

Many critics oppose seed oil, believing its unsaturated fats harm health. However, a study in the British Journal of Nutrition found that seed oils high in unsaturated fats, especially linoleic acid, may lower the risk of heart disease. The American Heart Association also supports omega-6s as part of a heart-healthy diet.

Also, contrary to claims that seed oils cause inflammation, a 2024 Food & Nutrition Research review found that oils rich in unsaturated fats support better LDL cholesterol, weight control, and inflammation compared to saturated fats like butter and coconut oil.

So, what happens when you stop eating seed oils? Well, you likely miss out on their healthy fats, such as omega-3 and omega-6, which, according to research, support heart health and cholesterol levels.

When does seed oil become bad for you?

So, are seed oils bad for you? The answer is it depends. 

Guy Crosby, a nutrition expert at Harvard, says cooking with seed oils at home is not a problem. However, seed oils become bad for the health when repeatedly heated to high temperatures, like in restaurant deep fryers with rarely changed oil. This can create harmful compounds that affect health.

Jason S. Ewoldt, a dietitian at Mayo Clinic, backs this up by explaining that seed oils are often found in processed foods, which is why they are seen as “unhealthy.” However, seed oil itself is not the main problem, according to him. 

“The seed oil is not the likely driver for negative health effects,” Ewoldt said.

He added: “These processed foods also tend to have higher levels of refined carbohydrates, salt and sugar, which are all things we know in excess can impact health negatively.”

In the U.S., people now consume 15 times more omega-6s than omega-3s, partly due to increased seed oil intake. This imbalance has been linked to mood disorders, joint pain, menstrual pain, and even preterm birth.

What is concerning is that omega-6 levels and ratios vary widely among seed oils. Safflower oil has a ratio of 125:1, sunflower oil 91:1, and corn oil 50:1. In contrast, soybean oil and canola oil have much lower ratios at 8:1 and 2:1, respectively.

According to the National Institutes of Health, a lower omega-6 to omega-3 ratio can help reduce the risk of many chronic diseases common in Western societies.

The table above shows the omega-6 to omega-3 ratio for different types of oil.

The bottom line

Seed oils are inherently not harmful, but they become bad for health when repeatedly heated to high temperatures and infrequently changed. However, dismissing them entirely based on TikTok health gurus is misleading. 

Remember, seed oils high in unsaturated fats, especially linoleic acid, may help lower the risk of heart disease. So instead of avoiding them completely, focus on proper use—avoid overheating and limit foods cooked in reused oils.

Some of the images in this post were created with the help of AI image-generation tools to visually enhance the content.

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