“Seed oils” has become a buzzword on social media, often accompanied by claims that they are toxic. The reality is more nuanced. Here is what seed oils are and what the evidence says.
What counts as a seed oil
Seed oils are vegetable oils extracted from the seeds of plants. The ones most often discussed are:
- Canola (rapeseed) oil
- Soybean oil
- Corn oil
- Sunflower and safflower oil
- Cottonseed oil
- Grapeseed and rice bran oil
Olive oil and avocado oil come from the fruit, not the seed, so they are not usually included.
How they are made
Most supermarket seed oils are produced industrially: seeds are pressed, the oil is extracted with a solvent (usually hexane), then refined, bleached and deodorized to give a neutral taste and a high smoke point. “Cold-pressed” or “expeller-pressed” versions skip the solvent step.
Why they are criticized
Critics argue that seed oils are high in omega-6 fatty acids (mostly linoleic acid), that they cause inflammation, that processing leaves harmful residues, and that they are behind rising rates of chronic disease.
What the evidence says
- Major health organizations, including the American Heart Association and the US Dietary Guidelines, recommend replacing saturated fats (butter, lard, fatty meat) with unsaturated fats, which include most seed oils. Studies link this swap to lower LDL cholesterol and lower heart disease risk.
- Linoleic acid in the diet has not been shown to increase markers of inflammation in human studies, despite theories that it should.
- Residual hexane in refined oils is present at very low levels; regulators consider it safe, although it is a common point of debate.
- Repeatedly reheating any oil at high temperatures, as in commercial deep fryers, produces degradation compounds. That is a concern about how oil is used, not about seed oils in a home kitchen.
The Harvard T.H. Chan School of Public Health’s Nutrition Source summarizes this research for the public.
The real issue: ultra-processed food
Much of the seed oil people eat comes from chips, fried fast food, pastries and packaged snacks. Those foods are worth limiting, but mainly because they are ultra-processed, high in calories, salt and refined carbs. Cutting them improves a diet whether or not the oil is to blame.
Practical takeaways
- Use a variety of oils: extra virgin olive oil as a main cooking oil, canola for neutral high-heat cooking, and others for flavor.
- Limit deep-fried and ultra-processed foods.
- Do not replace seed oils with large amounts of butter or tallow on the belief that saturated fat is healthier; the evidence points the other way.
Which oil to use for which cooking method is covered in the healthiest cooking oils. Fat in general is discussed in the best ways to eat more healthy fats.
