Why industrial seed oils are red-flagged
Refined seed oils — canola, soybean, sunflower, cottonseed, corn, grapeseed, rice bran — are the default cooking fat in most packaged food, café kitchens, and takeaway. The directory puts the solvent-extracted versions in the red-flag tier. Here's the reasoning, including the parts that are still debated.
How they're made
Getting oil out of a seed that's only a few percent oil by weight takes an industrial process: the seeds are cleaned, heated, pressed, then washed with a petroleum solvent (usually hexane) to strip the remaining oil. The crude oil is then degummed, bleached, and deodorised at high heat. That last step drives off the smell and taste of rancidity but can also generate oxidation and trans-fat by-products. The finished oil is shelf-stable, neutral, and cheap.
Cold-pressed olive oil, by contrast, is just pressed fruit — no solvent, no high-heat refining.
The omega-6 argument, and its limits
Seed oils are high in linoleic acid, an omega-6 fat. The body converts a fraction of it along a pathway that can produce pro-inflammatory signalling molecules. Diets very high in refined omega-6 are associated with higher inflammatory markers in some studies, and the modern omega-6 to omega-3 ratio is far higher than it was a century ago.
Where it gets contested: controlled trials swapping saturated fat for linoleic acid have generally shown lower LDL cholesterol, and large observational datasets don't consistently link linoleic acid intake to worse cardiovascular outcomes. So "omega-6 causes inflammation in humans" is not settled. The more defensible position is the one the directory takes — the refining process, the oxidation products, and the fact that these oils travel with ultra-processed food are reason enough to prefer stable, minimally processed fats.
What to cook with instead
✓ Prefer
- Extra-virgin olive oil (cold-pressed)
- Butter and ghee from pasture-raised cows
- Tallow and duck fat
- Coconut oil
- Cold-pressed avocado oil
✕ Red flag
- Canola / rapeseed oil
- Soybean & "vegetable" oil
- Sunflower & safflower (standard)
- Cottonseed, corn, grapeseed, rice bran
- Most margarine and "cooking spray"
Trade up, not junk: high-oleic sunflower oil is lower in linoleic acid and more heat-stable — a reasonable middle option, but still refined.
Reading the label
On an ingredient list, "vegetable oil" almost always means soybean or canola. "May contain canola and/or sunflower oil" means whichever was cheapest that week. The directory flags specific Australian products — spreads, mayonnaise, chips, crackers — by tier.