Seed Oils – Bad Press(ed): Myth-Busting Misinformation
By Isabel Somers Kelly, MSc Nutrition, University of Leeds
What are seed oils, why are we scared of them, and how do they impact our health?
What Are Seed Oils?
Seed oils are vegetable fats extracted from crop seeds. The most common seed oils in the UK are:
- Sunflower
- Rapeseed (UK)/Canola (USA)
- Soybean
- Corn
- Cottonseed
- Safflower
- Grapeseed
- Rice bran
These oils are a common staple in both home kitchens and commercially in the food industry due to their affordability, neutral flavour, and high smoke points.
Most seed oils are produced through a process that involves mechanical pressing or chemical extraction using a food-grade solvent, such as hexane. This method increases yield by breaking down plant cell walls, followed by refining, bleaching, and deodorising to remove impurities and ensure the oil is stable, safe, and suitable for cooking. Although the use of hexane has raised concerns, it is effectively removed during manufacturing, with only trace residual amounts (0.8mg/kg oil) – a standardised process that’s tightly regulated by both the EU and FDA. The primary source of hexane ingestion comes from gasoline fumes, with less than 2% coming from food sources. There is no evidence to show that remaining trace residues of hexane in food products pose any risk to human health.
Cold Pressed Oils
Not all seed oils are produced using solvent extraction. Cold-pressed oils, such as flaxseed and some varieties of rapeseed oil, are mechanically extracted without the use of heat or chemical solvents. While they tend to be more expensive and less stable at high temperatures, the gentler process helps preserve sensitive nutrients, including omega-3 fatty acids and natural antioxidants. Unrefined oils retain more nutrients and are best used unheated, or for low-heat cooking.
In plant-based and omnivorous diets, both refined and cold-pressed seed oils can serve as a key source of unsaturated fats, including essential omega-6 and omega-3 fatty acids.
Myth 1: Seed Oils Are “Toxic” and “Inflammatory”
One of the most widespread myths is that seed oils promote inflammation and are toxic to human health.
This claim is based on the fact that seed oils are rich in omega-6 polyunsaturated fatty acids (PUFAs), particularly linoleic acid, an essential omega-6 fatty acid that the body cannot produce on its own. Some concerns have been raised about the metabolism of linoleic acid into compounds that can contribute to inflammatory markers. This has led to the assertion that seed oils are inherently inflammatory due to their composition of omega-6 content. However, this is a misrepresentation of the complex metabolic pathways of dietary linoleic acid and is not supported by current scientific evidence. These claims are often promoted by individuals on social media with ideological or commercial motives, rather than by experts in nutritional science.
Current evidence does not support the myth that dietary linoleic acid causes systemic inflammation in healthy individuals. A systematic review of 15 randomised controlled trials found no scientific evidence to suggest that dietary linoleic acid intake increases inflammatory markers in healthy people, helping to dispel the myth that seed oils are pro-inflammatory or “toxic” to human health.
Myth 2: Seed Oils Cause Chronic Diseases
Seed oils are often blamed for rising rates of obesity, type 2 diabetes, and cardiovascular disease.
This claim is largely rooted in the fact that seed oils are commonly used in ultra-processed foods (UPFs), which are typically high in salt, sugar, and fat (HFSS). Diets high in these foods are consistently linked to inflammation and insulin resistance, increasing the risk of chronic conditions like cardiovascular diseases and bowel cancer.
Additionally, the industrial processing of seed oils is often portrayed as inherently harmful, contributing to the perception that they are unhealthy. However, this narrative overlooks the nutritional profile of seed oils themselves and unfairly places blame on a single ingredient. Chronic diseases are not caused by one food component alone; rather, they result from overall dietary patterns and lifestyle factors.
There is no evidence to support the myth that seed oils themselves cause chronic disease. On the contrary, a review of clinical trials and meta-analyses has shown that higher intake of PUFAs, especially linoleic acid, may reduce the risk of cardiovascular disease. Linoleic acid has been shown to lower cholesterol and may improve glucose metabolism, supporting metabolic health, rather than harming it.
Further, a large 2025 prospective cohort study involving 221,054 adults found that replacing saturated animal fats with unsaturated fats from plant oils improved blood lipid profiles and reduced the risk of cardiovascular disease. Additionally, a higher intake of plant-based oils was associated with lower mortality. When consumed as part of a balanced, whole-food, plant-based diet, seed oils can support cardiovascular and metabolic health and are recommended by public health organisations as part of a heart-healthy eating pattern.
Myth 3: You Shouldn’t Cook with Seed Oils
Concerns about cooking with seed oils often focus on the formation of harmful compounds through oxidation when these oils are repeatedly heated at high temperatures.
This is a standard cooking method in commercial and fast food restaurants, which can lead to oxidation and the formation of aldehydes. While these compounds may be harmful in large quantities, it is widely understood that regardless of the type of oil used, deep-fried foods should be limited as part of a balanced diet.
Most seed oils, such as sunflower and rapeseed (or vegetable oil), have high smoke points and are stable when used in home cooking. When used fresh and not overheated or reused, they are fine to be heated lightly for sautéing, baking, and frying. Moderate consumption of plant oils, especially cold-pressed and unheated, in salads and dressings, for example, is understood to be perfectly safe and may contribute to better health compared to the consumption of saturated animal fats.
Myth 4: Seed Oils Are “Unnatural”
Seed oils are often dismissed as “unnatural” or “industrial,” while animal fats like butter or beef tallow are promoted as more “traditional” and “healthier” alternatives.
This argument is rooted in naturalistic fallacy – the belief that what is “natural” is inherently better or healthier. This narrative has gained traction in online wellness communities and political rhetoric in the US, where Robert F. Kennedy Jr. has been publicly demonising seed oils and promoting beef tallow as a superior alternative. However, these claims are not backed by science and raise concerns about the spread of health misinformation and its impact on public health.
All edible oils, whether from seeds, fruits, or animals, must be processed to some degree. The idea that seed oils are harmful simply because they are refined is not supported by evidence. While beef tallow may be marketed as “natural”, it is still a processed product, very high in saturated fat, which is strongly linked to elevated LDL cholesterol and increased cardiovascular risk.
The NHS advises that unsaturated fat from plant sources should be favoured in place of saturated animal-based fats, such as dairy and meat sources, for overall health. The idea promoted by this myth that we should replace seed oils, a source of unsaturated fat, with high saturated fat options like beef tallow, cannot be considered a health recommendation, as it may increase the risk of cardiovascular disease and stroke, according to the NHS dietary guidance.
Replacing animal fats with plant-based fats, including seed oils, can be used to improve heart health and prevent disease, dispelling the fallacy that “natural” and “traditional” always means healthier.
Conclusion
Seed oils continue to be a divisive, often misrepresented topic in modern nutrition discourse, targeted by a wave of misinformation that often favours fear over fact. Yet the scientific consensus is clear: when used appropriately and in moderation, seed oils are not toxic, inflammatory, or inherently harmful. On the contrary, they can contribute to a balanced and healthy plant-based diet, thanks to their rich content of unsaturated fats and essential fatty acids. Health authorities recommend replacing saturated fats such as tallow and butter with unsaturated fats from plant-based sources. Choosing cold-pressed, less refined options such as flaxseed, olive, and avocado oil can offer additional benefits.
The true threat is not in these oils themselves, but in the viral spread of dietary misinformation. Demonising singular ingredients distracts from what matters most, the quality of our overall diets and the broader lifestyle patterns that shape our health.