Over the past century, industrial food processing has compromised food quality in exchange for shelf-stability and cost-effectiveness, which resulted in seed oils replacing animal fats and cold-pressed oils.
As chronic diseases rise and social media sparks interest in healthy eating, many are questioning the safety of these products, but identifying a truly healthy cooking oil can be challenging.
Discover the worst seed oil for your health and explore healthier alternatives to choose instead.
What are seed oils?
Seed oils, often misleadingly marketed as vegetable oils, are fats extracted from the seeds of soybean, canola, corn, cottonseed, rice bran, grapeseed, sunflower, and safflower plants.
Unlike foods naturally rich in oils such as coconuts, olives, or avocados, these seeds are much lower in fat, usually containing only about 20 percent oil.
To extract these fats and make them palatable, they require extensive industrial processing that involves high pressure, chemical processing, and high-heat deodorization.
Because of their low production costs and long shelf life, seed oils have become especially popular in processed foods. They’re also commonly used in restaurant fryers, condiments, desserts, and even pet food, where they replace natural fats and serve as the main source of unsaturated fats in Western diets.
However, seed oils’ fatty acid profile and processing methods are linked to chronic health issues, including obesity, heart disease, and inflammation.
Watch the video below to learn which cooking oils you should keep out of your kitchen.
From waste product to cooking oil
Historically, many seed oils entered the food supply not because they were valued culinary ingredients, but because they were cheap industrial byproducts.
For instance, cottonseed oil began as textile waste used for lamp fuel, candle-making, and fertilizers before being refined for food. Similarly, canola oil started as an industrial lubricant for machinery until it was developed for human consumption.
This practice, known as industrial byproduct valorization, is a common way for industries to turn surplus waste materials into revenue.
While it may conserve resources, research published in Trends in Food Science & Technology warns that the lack of regulatory safety guidelines poses significant risks to human health.1
Why seed oils are harmful
Weak regulatory oversight in the food industry has allowed highly refined seed oils to be marketed as heart-healthy, relying on outdated, often industry-funded research that has long been disputed.
The dangers of seed oils arise from their unstable fatty acid profile and industrial processing.
Imbalance of essential fats
Most seed oils contain excessive concentrations of omega-6 polyunsaturated fats, while lacking adequate amounts of omega-3 fatty acids.
Omega-3 fatty acids–found in oily fish, shellfish, seeds, and nuts–are vital for maintaining healthy cell membranes, brain function, vision, and cardiovascular health, and support the body’s ability to regulate inflammation.
Omega-6 fats support growth, repair, and immune activity, but excessive intake can displace omega-3 fatty acids by competing for the same enzymes and membrane incorporation pathways.
This imbalance promotes the release of pro-inflammatory compounds, impairing the body’s ability to regulate inflammation, which can damage the body over time.
Shockingly, in modern Western diets, the typical omega-6 to omega-3 ratio can exceed 50:1, far above the recommended 1:1 to 4:1.
A study published in Prostaglandins & Other Lipid Mediators found that immune cells in the brain with omega-6 to omega-3 ratios around 7:1 or 2:1 showed better cell function and reduced inflammatory responses than those with higher ratios.2
Smoke point vs. peroxide value
It’s widely believed that a high smoke point means an oil is safe for cooking, but this can be misleading.
The smoke point only indicates when an oil starts to burn visibly, while the peroxide value measures oxidative damage that can occur well before smoke appears.
Research published in Advances in Nutrition highlights that polyunsaturated fatty acids (PUFAs) are highly unstable and can undergo spontaneous oxidation when exposed to oxygen, a process known as lipid peroxidation.3
This oxidation produces toxic byproducts such as aldehydes, which can harm cells and promote inflammation, and can occur anytime PUFAs are exposed to oxygen, including during storage, processing, transport, or cooking.
Furthermore, seed oils are refined with high heat and chemical solvents, so they may already have elevated peroxide values before being used in cooking applications.
8 toxic seed oils
Most seed oils are highly processed, rich in unstable omega-6 fats, and low in nutrients. Avoiding these cooking oils is an excellent strategy to support your health.
Here are eight toxic seed oils to avoid when pursuing a healthy diet.
1. Cottonseed oil
Cottonseed oil is exceptionally high in omega-6 fatty acids and is typically derived from pesticide-treated crops. Heavy refining is also required to remove gossypol, a naturally occurring toxin, but traces may still remain in the final product.
Historically, cottonseed oil was partially hydrogenated to produce margarine, vegetable shortening, and other solid fats for baking.
Partially hydrogenated seed oils contain artificial trans fats, which have now been banned in the U.S. due to their strong link to systemic inflammation and metabolic dysfunction.
Cottonseed oils are common in packaged snacks and fried foods and can even be found in various skin-care products.
2. Soybean oil
Soybean oil is one of the leading sources of dietary omega-6 fats in the U.S and is one of the most frequently used oils in fast food restaurants and processed foods.
It’s commonly hydrogenated and frequently derived from genetically modified (GMO) soybeans. This means the soybeans were likely exposed to glyphosate, a pesticide that has been linked to gut microbiome imbalances, fertility issues, neurodegenerative disorders, and liver diseases.
3. Corn oil
Corn oil is almost always derived from GMO crops and is prone to glyphosate exposure. It’s high in linoleic acid and contains an omega-6 to omega-3 ratio of 83:1, making it a highly pro-inflammatory cooking oil.
It’s widely used in soaps, shampoos, household cleaners, and cosmetics, as well as for deep frying and the production of hydrogenated margarine.
4. Canola oil
Extracted from heavily processed rapeseeds and typically refined, bleached, and deodorized, canola oil is also commonly hydrogenated and derived from GMO crops.
Canola is a widely used ingredient in mass-produced desserts, pastries, and snack cakes, as well as salad dressings and mayonnaise.
5. Sunflower oil
According to data published in the Journal of Lipids, sunflower oil is exceptionally high in omega-6 fats while containing little to no omega-3 fatty acids, with a total ratio of 632:1.4
This oil can be found in popular processed foods, including potato chips, crackers, granola bars, and commercial salad dressings.
6. Safflower oil
Although marketed for high-heat use, safflower oil can oxidize quickly and generate harmful compounds due to its high PUFA content.
It’s typically found in baked goods, snacks, and processed sauces.
7. Grapeseed oil
Grapeseed oil is a byproduct of winemaking that’s often solvent-extracted and refined.
It oxidizes easily, and while more research is needed, it’s estimated to have an omega-6 to omega-3 ratio range of up to 700:1, indicating its high potential for promoting inflammation and associated health issues.
8. Rice bran oil
Rice bran oil is typically used in packaged foods, for deep frying, and in beauty products; sometimes blended with other vegetable oils.
Despite being marketed as having a high smoke point, rice bran oil is highly prone to rapid oxidation, even at room temperature.
A study published in Food Research International found that free fatty acids in stored rice bran tripled in just 14 days due to natural enzyme activity. This activity can rapidly degrade oil quality and increase lipid oxidation before it even reaches the consumer.5
What is the worst seed oil?
“Out of the common seed oils, aptly known as the Hateful Eight, cottonseed oil is by far one of the most toxic,” explains Dr. Berg. “It contains chemical residues, goes rancid easily, and is hidden in countless processed foods.”
Cottonseed oil’s fatty acid profile is significantly imbalanced, containing excessive concentrations of omega-6 fats while offering almost no omega-3s. It also has poor oxidative stability, making it unsuitable for cooking and potentially harmful to overall health.
Because cotton is grown primarily as a textile crop, pesticide regulations are less strict than those for food crops. Its heavy pesticide use has earned cotton the nickname “dirtiest crop in the world,” making cottonseed oil a questionable choice for consumption.
According to data published by the United States Department of Agriculture (USDA), surveying 92 percent of U.S. cotton, herbicides were applied to 96 percent of the crops, with up to 45 percent of those treated with glyphosate.6
Moreover, most cotton varieties are genetically engineered, and many are modified with Bacillus thuringiensis (Bt), a bacterium that destroys insects’ gut cells. While this targets pests, it raises concerns about unintended effects on the human microbiome.
Healthy alternatives to seed oils
Eliminating seed oils and replacing them with healthy fats that are nutrient-dense and heat-stable can significantly improve the nutritional quality of meals and support better fatty acid balance.
Health-promoting saturated fats found in grass-fed butter, ghee, beef tallow, and unrefined coconut oil are ideal for high-heat cooking due to their oxidation resistance.
These fats also provide essential fat-soluble vitamins that support hormone production, brain function, and cellular health, especially when paired with a low-carbohydrate diet.
Cold-pressed extra virgin olive oil and unrefined avocado oil are excellent choices for cooking at low to medium heat. They provide monounsaturated fats and antioxidants that help protect delicate fatty acids from oxidation.
Sustainably sourced palm oil contains vitamin E and beta carotene, has lower pesticide exposure than soy or corn oil, and is more heat-stable than many harmful seed oils. It’s best to opt for minimally processed red palm oil to maximize health benefits and nutritional value.
For frying, use stable fat sources such as grass-fed beef tallow instead of seed oils and avoid extremely high temperatures that naturally promote lipid oxidation. Consider air frying or oven roasting over deep-frying, which requires less oil while achieving similar textures and flavor.
Key takeaways
Industrial seed oils are high in unstable omega-6 fats, prone to oxidation, and often chemically processed. Regular consumption can disrupt the body’s inflammatory balance, metabolic health, and digestive functions.
While most of these oils pose health risks, cottonseed oil stands out as the worst seed oil for its excessive chemical exposure, heavy processing, and extremely high omega-6 fat content.
Replacing industrial seed oils with stable fats such as grass-fed tallow, butter, ghee, or coconut oil can help maintain metabolic balance, support cellular health, and promote overall health and well-being.
FAQ
What are seed oils, and why should I avoid them?
Seed oils are fats extracted from commercial crops such as soybeans, corn, cottonseed, sunflower, safflower, and canola, and are typically processed with chemical solvents, bleaching agents, and high-heat deodorization.
It’s vital to avoid seed oils, as they increase exposure to chemical residues and have an unfavorable omega-6 to omega-3 fatty acid ratio linked to inflammation, poor metabolic health, weight gain, and heart disease.
What is the worst seed oil?
Cottonseed oil is the worst seed oil due to its significant omega-6 to omega-3 fatty acid imbalance, low oxidative stability, and high risk of chemical contamination.
What is the best oil to cook with?
Some of the best oils for cooking include stable, saturated fats such as unrefined coconut oil, grass-fed tallow, or ghee.
Grass-fed butter, cold-pressed extra virgin olive oil, and unrefined avocado oil work well for medium to low heat and provide beneficial antioxidants and heart-friendly monounsaturated fats.
What is the healthiest oil to deep fry with?
The healthiest oil for deep frying has a high smoke point and contains stable saturated or monounsaturated fats that resist oxidation. Beef tallow, lard, ghee, and coconut oil are excellent choices known for their exceptional heat stability.
Sources
- https://www.sciencedirect.com/science/article/pii/S0924224421003174 ?
- https://www.sciencedirect.com/science/article/abs/pii/S1098882323000369?via%3Dihub ?
- https://www.sciencedirect.com/science/article/pii/S2161831322001235 ?
- https://pmc.ncbi.nlm.nih.gov/articles/PMC7990530/ ?
- https://www.sciencedirect.com/science/article/abs/pii/S0963996924003132 ?
- https://www.nass.usda.gov/Surveys/Guide_to_NASS_Surveys/Chemical_Use/2021_Field_Crops/chemhighlights-cotton.pdf ?
