What Are Seed Oils? An Honest Guide to the Most Argued-About Fats in Your Kitchen

Few words have done more shouting on the internet in the last two years than seed oils. They have been called poison and they have been called harmless, often in the same afternoon, usually by people selling something. We press olive oil for a living, so we have an obvious stake in this argument. That is exactly why we are going to be careful with it.

Here is what a seed oil actually is, how one is made, what the research genuinely shows, and what we think a cook should reasonably do about it.

What Is a Seed Oil?

A seed oil is an edible oil extracted from the seed of a plant rather than from its fruit. That is the whole definition. It is a botanical distinction, not a moral one.

The oils usually meant by the term are:

• Soybean oil
• Canola (rapeseed) oil
• Corn oil
• Sunflower oil
• Safflower oil
• Cottonseed oil
• Grapeseed oil
• Rice bran oil
• Peanut (groundnut) oil

Some lists run to eight, some to a dozen. There is no official register — the phrase was coined in popular nutrition writing, not in food law.

Which Oils Are Not Seed Oils

Olive oil is not a seed oil. Neither are avocado oil, palm oil, or coconut oil. All four are pressed from the flesh of a fruit. An olive is a drupe — a stone fruit, cousin to a plum — and the oil lives in the pulp around the pit, not inside it. We wrote a fuller explanation in Is Olive Oil a Seed Oil?, because the question arrives in our inbox most weeks.

Butter, lard and ghee are animal fats and sit outside the category entirely.

How Seed Oils Are Made — and Why That Matters More Than the Seed

This is the part most of the argument skips, and it is the part that actually deserves attention.

Seeds are stingy. A sunflower seed or a soybean holds relatively little oil, and it is locked in tightly. Pressing alone leaves too much behind to be commercially viable at scale, so the standard industrial route adds steps:

1. Crushing and heating. The seed is cleaned, cracked, flaked and warmed to loosen the oil.
2. Solvent extraction. The material is washed with a food-grade solvent, typically hexane, which dissolves out the remaining oil. The solvent is then evaporated off and recovered.
3. Refining, bleaching, deodorising. The crude oil is treated with alkali, filtered through bleaching clay, and steam-stripped at high temperature to strip colour, aroma and free fatty acids.

What comes out is pale, neutral, shelf-stable and cheap. That is not an accident — it is the design brief. A food manufacturer wants a fat that tastes of nothing, lasts for months, and costs very little per tonne. Refined seed oil does that job better than anything else on earth.

Extra virgin olive oil is made by the opposite logic. Olives are crushed and the oil is separated mechanically, at low temperature, with no solvents and no refining at all. Everything that makes it taste of something — the bitterness, the pepper, the grass — is a fragile compound that any refining step would remove. That is why our process is short and our harvest window is measured in days rather than months; we walked through it step by step in From Grove to Bottle.

So the honest framing is not seed versus fruit. It is refined versus unrefined. Cold-pressed sunflower oil and refined olive oil both exist, and both cut across the tidy categories people argue about.

What the Evidence Actually Says

Here we are going to disappoint the people who want a villain.

The central charge against seed oils is that they are high in omega-6 linoleic acid, that linoleic acid promotes inflammation, and that the modern rise in seed oil consumption therefore drives chronic disease. The first part is true — soybean, corn, sunflower and safflower oils are indeed linoleic-acid-rich. The rest is where it gets complicated.

Large observational studies and randomised trials have generally not found that replacing saturated fat with polyunsaturated vegetable oil worsens cardiovascular outcomes; several found modest improvement in blood lipids. Major heart and nutrition bodies continue to treat these oils as acceptable replacements for saturated fat. Critics counter that much of this literature is short-term, that biomarkers are not the same as hard outcomes, and that some older trial data was re-analysed to less flattering effect. Both of those criticisms have merit. The truthful summary is that this is an unsettled scientific argument, not a closed case in either direction.

We are an olive oil company. It would be easy money for us to tell you seed oils are poison. We are not going to, because we do not think the evidence supports the word.

What We Think Is the Stronger Argument

The real issue with seed oils in a modern diet is less about the molecule and more about the company it keeps. Refined seed oil is the cheapest calorie in the industrial pantry, which means it is overwhelmingly consumed inside ultra-processed food — fried snacks, packaged baked goods, sauces, fast food. Those foods carry their own well-documented problems. Blaming the oil alone is like blaming the flour in a doughnut.

The second issue is sensory, and it is the one we care about most. A fat engineered to taste of nothing contributes nothing. Cook with it for a year and your food is built on a blank.

The Case for Extra Virgin Olive Oil

The evidence for extra virgin olive oil is unusually good — not because it is a miracle, but because it has been studied hard and for a long time, mostly as part of a Mediterranean pattern of eating. Two things distinguish it from any refined oil:

Monounsaturated backbone. Olive oil is roughly 70–80% oleic acid, a stable monounsaturated fat, with far less polyunsaturated content than the linoleic-heavy seed oils. That stability is also why it handles a hot pan better than its reputation suggests.

Polyphenols. Refining destroys them; cold extraction preserves them. These are the compounds behind the bitterness on the tongue and the pepper at the back of the throat, and they are the same compounds that carry most of olive oil’s measured antioxidant activity. A refined oil has essentially none. We go deep on this in High-Polyphenol Olive Oil.

Freshness matters as much as origin. Polyphenols fade from the day the fruit is milled, which is why a harvest date on the label is worth more than a picture of a Tuscan hillside.

What We’d Actually Do in Your Kitchen

No purge, no panic. A sensible position:

• Make good olive oil your default. Sautéing, roasting, dressing, finishing — it handles nearly all of it, and it makes food taste better, which is reason enough.
• Worry about the food, not the fat in isolation. Cutting ultra-processed food does more for you than swapping which bottle the fryer uses.
• Keep a neutral oil if you need one. Deep-frying a large batch, or making a mayonnaise where olive flavour would dominate — a refined oil is a legitimate tool. Use it on purpose, not by default.
• Read the back label. “Vegetable oil” is a blend that can change between batches. If you cannot tell what is in the bottle, that is the more useful red flag. Our guide to reading an olive oil label applies the same scepticism to our own category.

The Olive Father Position

We do not sell fear. We sell one oil, from one family’s groves in San Procopio, Calabria, pressed within hours of picking, with a harvest date and a lot number on every bottle because we think you are owed the receipts.

If seed oils brought you here, stay for the better reason: unrefined fruit oil, made honestly and used fresh, is simply better cooking. Start with the range and taste the difference for yourself — then judge us on the pepper in the back of your throat, not on anyone’s headline.