Seed Oils | Ask the Expert

Seed oils divide opinion. Some people insist they are ultra-processed, toxic, and should be avoided at all costs. Other people say they are perfectly safe and can be part of a healthy diet. But what does the most up-to-date science tell us about seed oils?

Seed oils - like canola, sunflower, soybean, and corn oil - have sparked heated debates across the world. Many prominent authors, wellness influencers and popular podcasters have questioned what they are doing to our health. This movement has given rise to a “Seed Oil Free Certified” label in the United States, and its influence is beginning to spread in Europe. In countries like Germany and the UK, conversations around seed oils are becoming more common, particularly among people who want to eat natural, unprocessed foods. You might yourself have read some of the claims that seed oils cause inflammation, cancer, diabetes, and heart disease. 

Being open to new ideas and information is a good thing - because nutritional advice changes over time as new research emerges. Take eggs, for example. A few decades ago, we were told to limit them to two or three per week because of concerns about cholesterol. But as new research was done and our knowledge grew, we learned that eggs are actually a healthy and affordable food that the average healthy person can eat every day.¹ Dietary information evolves, and so can our food choices. But what does the most up-to-date science say about Seed Oils? Are they really as bad as people are saying?

To help separate fact from fiction, we deep-dived into the research with the help of Registered Nutritionist Sophie Gastman (RNutr Public Health). Let’s get to the bottom of the concerns around seed oils and whether they deserve their bad reputation.

What are seed oils, and how are they made? 

Seed oils are extracted by crushing the seeds to release oil. In industrial processes, this method involves additional processing compared to making oils from fruits like olives or avocados, as it often requires the use of solvents like hexane to extract more oil. While most hexane is removed, tiny traces can remain in cooking oils.

While this might sound concerning, there’s currently no evidence that the process makes these oils unsafe or toxic. In the EU, hexane residues in food are strictly limited to 1mg/kg, and research has not yet found evidence that these small amounts pose a health risk. In the US, the Food and Drug Administration (FDA) does not currently regulate hexane residues in cooking oils, so it’s unclear how much, if any, remains in supermarket products.^2,3,4,5 

Sunflower and canola are common examples of seed oils. 

Why are seed oils so popular?

Seed oils are widely used because they’re affordable, versatile, and have a high smoke point, which means they can be heated to high temperatures without breaking down or producing harmful compounds. The high smoke point makes them ideal for frying and other cooking methods.^{6, 2} 

Recently, there have been claims of seed oils being harmful to health, especially because of their so-called inflammatory properties—meaning they may contribute to inflammation in the body, a process linked to chronic diseases like heart disease and arthritis. Concerns about seed oils aren’t entirely unfounded, but the focus is often misplaced.

Repeatedly heating cooking oils - including seed oils - can make them oxidise, a process where they react with oxygen and break down, forming harmful compounds. You can reduce this risk by avoiding deep-fried foods like chips (potato fries). Instead, you can oven-bake potatoes for a healthier alternative, using only the oil you need.

Why do seed oils have a bad reputation?

A lot of the criticism around seed oils is their link with highly processed and fried foods. These unhealthy foods make up a significant part of modern diets, with the average European now getting nearly 30% of their energy from ultra-processed foods.⁷

Eating too many highly processed and fatty foods is indeed linked to chronic diseases. But nutritionist Sophie Gastman emphasises that the problem is more about overall diet quality than seed oils themselves. 

"It’s true that seed oils are cheap and therefore widely used in ultra-processed foods, which tend to be high in salt, sugar, and fat—a combo we know isn’t great for overall health," she explains. Because of this, seed oils have been unfairly blamed for the negative health effects of these foods. “When people cut out seed oils and say they feel better, it’s often because they’re eating fewer ultra-processed foods overall, not because seed oils are inherently bad,” Gastman adds.

“When people cut out seed oils and say they feel better, it’s often because they’re eating fewer ultra-processed foods overall, not because seed oils are inherently bad.”

What’s the deal with omega ratios?

Another concern about seed oils is the levels of omega-6 fatty acids they contain. Omega-6s are essential fats, meaning our bodies need them, but critics argue that too much omega-6, especially compared to omega-3s, could increase inflammation.⁶ 

This health concern isn’t unfounded. It’s true that Omega-3s are known for their anti-inflammatory properties, while omega-6s can produce compounds that are slightly pro-inflammatory.⁸ Compared to the traditional diets of early humans, where omega-6 and omega-3 fats were eaten in roughly equal amounts, modern diets now include 16 times more omega-6 fats than omega-3s. 

This change has raised concerns about increased inflammation, but a wide range of research suggests it’s not that simple. Gastman explains, “There’s a lot of alarmist talk about inflammation, but if we actually look at the science, there’s no solid evidence to support these claims. While omega-6s contain linoleic acid, which the body can convert into a compound involved in inflammation, only a tiny amount actually gets converted, and some research even suggests it may help reduce inflammation.”

Studies show that as long as you get enough omega-3s, the balance between omega-6 and omega-3 fats is less important than some believe. For example, the Food and Agriculture Organization (FAO) has stated there’s no need to focus on specific omega-6-to-3 ratios.^9,10,11,12

Looking to eat more Omega-3s? You can find Omega-3 in fatty fish, walnuts, and flaxseeds.

Are all seed oils the same?

If you’re looking for a seed oil with extra benefits, flaxseed oil is a standout because it’s high in alpha-linolenic acid (ALA), a type of omega-3. Keep in mind that flaxseed oil should not be used for cooking, as it does not have a high smoke point and can form harmful compounds when exposed to high heat. Gastman also highlights rapeseed oil as a particularly beneficial option, explaining, “Rapeseed oil provides a good balance of omega-3 and omega-6 fatty acids, plus key ingredients like Vitamin K and Vitamin E.” Still, no single oil is a magic fix. "Your overall diet and lifestyle will always have a greater impact on your health than whether or not you cook with seed oils," she adds.^13,14

"Your overall diet and lifestyle will always have a greater impact on your health than whether or not you cook with seed oils."

Flaxseed is high in alpha-linolenic acid (ALA), a type of omega-3.

What can I replace seed oils with?

Many critics of seed oils advocate for using animal-based fats like tallow or butter instead. In moderation, these fats can contribute to a nutrient-dense and balanced diet. But they’re high in saturated fat, which can raise non-HDL (‘bad’) cholesterol and increase the risk of heart disease and stroke in the long term.¹⁵

If you’re looking for an alternative to seed oils, olive oil—especially extra virgin olive oil—is a great choice. It’s high in healthy fats that support heart health and contains natural antioxidants and vitamins that help protect your body. Because it’s less processed, extra virgin olive oil keeps more of these beneficial nutrients compared to refined oils. However, olive oil is significantly more expensive than seed oils. For instance, in Dutch supermarkets, a litre of classic olive oil costs between €9 and €10, while seed oils like rapeseed oil are priced at approximately €1.30 per litre. This substantial price difference makes olive oil less accessible to many people.¹⁶

The verdict - an informed approach to cooking oils

What you choose to eat depends on so many things - from where you live to what you like eating, your weekly food budget and your personal health situation. So, if you prefer to avoid seed oils as a precaution, that’s entirely your choice.

But the takeaway message from our research is that seed oils aren’t inherently bad. The bigger issue is that they’re commonly used in ultra-processed and fried foods, like crisps, fast food, and packaged snacks. These foods are often high in calories and low in nutrients, contributing to poor health outcomes when we eat too much of them.  

Gastman suggests, "If most of your diet is made up of ultra-processed foods and lacking in fibre, then it’s worth thinking about ways to bring in more whole foods and reduce the amounts of ultra-processed foods. But if you’re using these oils as part of a balanced, varied diet, there’s no reason to avoid them."