The Seed Oil Glossary

Seed oil

An industrial cooking oil pressed or solvent-extracted from seeds: soybean, canola (rapeseed), corn, sunflower, safflower, cottonseed, grapeseed, and rice bran oil. They entered the food supply in the early 1900s and now dominate restaurant fryers and packaged food.

PUFA

Polyunsaturated fatty acid — a fat molecule with two or more double bonds, which makes it chemically unstable and prone to oxidation, especially under heat and light. Seed oils are the most concentrated dietary source. This entire site measures estimated PUFA grams.

Linoleic acid

The specific omega-6 PUFA that makes up most of the fat in seed oils — soybean oil is over half linoleic acid. Modern intake is several times higher than at any point before the 20th century, which is the core concern of the seed-oil-free community. See the studies on our Evidence page.

Omega-6 / Omega-3

Two families of PUFA, named for where the first double bond sits. Both are essential in small amounts; the modern diet skews heavily omega-6 (mostly linoleic acid from seed oils), and many researchers argue the ratio matters as much as the total.

Oxidation

The chemical breakdown of unstable fats when exposed to heat, light, or air — producing compounds like aldehydes. PUFAs oxidize far more readily than saturated or monounsaturated fats, which is why repeatedly-heated seed-oil fryer oil is the worst case.

High-oleic

A bred variety of sunflower, safflower, or canola whose fat is mostly oleic acid (the stable monounsaturated fat in olive oil) instead of linoleic acid. High-oleic sunflower oil can be under 10% PUFA versus about 66% for regular sunflower oil — a big difference hiding behind one word on a label.

Hydrogenation

An industrial process that hardens liquid oil into shortening or margarine by adding hydrogen. Partial hydrogenation creates trans fats, now banned in the US; fully hydrogenated oils and palm blends replaced them in most products.

"Vegetable oil"

A labeling term that almost never means vegetables — in the US it is usually soybean oil, sometimes blended with canola, corn, or cottonseed. Check the ingredient list in parentheses for the actual oils.

Tallow

Rendered beef fat — the traditional deep-frying fat (McDonald's fried in it until 1990). Mostly saturated and monounsaturated, only ~4% PUFA, and very stable at fryer temperatures. See which chains use it on our Tallow Watch page.

Smoke point

The temperature where an oil visibly smokes. Often cited as the measure of cooking safety, but stability matters more: PUFAs oxidize well below the smoke point, while saturated fats like tallow and coconut oil stay intact.

Cold-pressed vs refined

Cold-pressed (or "extra virgin") oils are mechanically squeezed and keep their antioxidants; refined oils are extracted with heat and solvents, then bleached and deodorized. Refining strips protective compounds but does not change the PUFA content — a refined seed oil is still high-PUFA.

Saturated & monounsaturated fat

The two stable fat families. Saturated fat (butter, tallow, coconut) has no double bonds and resists oxidation completely; monounsaturated fat (olive, avocado, most of the fat in beef) has one. Neither carries the oxidation problem that defines PUFAs.