The discourse on seed oils is louder than the data. The data is more boring and more useful. Across pooled randomised trials and large prospective cohorts, replacing saturated fat with linoleic acid lowers LDL and tracks with lower cardiovascular events. The practical question is not "are seed oils poison" but "in what form, how processed, and inside what diet."

What the 2026 evidence actually says

Linoleic acid, the omega-6 fatty acid that dominates sunflower, soybean, canola, and corn oils, is the molecule under fire. The largest pooled analyses tell a consistent story. Higher circulating linoleic acid associates with lower coronary heart disease and lower type 2 diabetes incidence in cohort data. Randomised trials swapping saturated fat for polyunsaturated fat reduce LDL cholesterol and lower cardiovascular events on average.

Three caveats matter. First, "seed oil" is a category, not a molecule. The fatty acid profile of cold-pressed canola differs from heavily refined soybean oil, which differs again from the reused fryer oil at a takeaway. Second, the trials test oils inside whole diets, not oils poured onto ultra-processed food. Third, the inflammation claim that linoleic acid raises CRP or arachidonic-acid-derived inflammation has not held up in controlled feeding trials. Linoleic acid does not reliably increase arachidonic acid in human tissue.

That is the boring read. The hot takes on either side overstate it.

Where the real signal sits: oxidation and processing

The interesting question is not the fatty acid. It is what happens to the fatty acid before it reaches the plate.

Polyunsaturated fats oxidise faster than saturated or monounsaturated fats. Heat, light, oxygen, and time accelerate it. When oils are heated repeatedly, as in commercial deep frying, oxidation products accumulate: aldehydes, lipid hydroperoxides, polar compounds. These are measurable, and at high enough exposures they have biological effects worth taking seriously.

This is why the same oil can sit in two different risk categories depending on use:

  • A bottle of fresh high-oleic sunflower oil used once for a stir-fry: low concern.
  • The same oil reused six times in a fryer at a fast-food outlet: a different product, chemically.

The seed-oil debate often collapses these into one. They are not the same.

The fatty acid on the label tells you less than the processing history, the storage, and the heat the oil has seen.

Linoleic acid and inflammation: the claim, and the data

The popular argument runs: omega-6 fats fuel arachidonic acid, arachidonic acid fuels inflammatory eicosanoids, therefore seed oils drive chronic inflammation. The biochemistry sounds tidy. The human data does not back it.

Controlled feeding studies that raise dietary linoleic acid do not consistently raise tissue arachidonic acid in adults. Markers like CRP and IL-6 do not move in a clear direction when linoleic acid is increased within normal dietary ranges. The conversion from linoleic acid to arachidonic acid in humans is tightly regulated and slow.

What does drive systemic inflammation in the data: excess body fat, poor sleep, low cardiorespiratory fitness, low fibre intake, and ultra-processed food patterns. Seed oils correlate with that last category because biscuits, chips, and takeaways use them. Confounding the oil with the food it rides in is the most common mistake in this conversation.

A practical NZ kitchen read

Here is how this lands in a Christchurch pantry without overthinking it.

Use olive oil as the default for low and medium heat. Extra virgin for dressings and finishing. Standard olive oil for pan work. It is monounsaturated-dominant, oxidatively stable enough for home cooking, and the cardiovascular evidence is the strongest of any fat.

For higher heat, avocado oil and high-oleic versions of canola or sunflower handle it. Butter and ghee are fine in moderate amounts. The saturated-fat-versus-polyunsaturated-fat trial data favours polyunsaturated for LDL, but the difference at household quantities is smaller than people think when the rest of the diet is built well.

Buy oils in dark bottles or tins. Store away from the stove. Replace them when they smell off. Rancid oil tastes like crayons or old paint, and the nose is a decent first-pass test.

The food matters more than the oil. Kūmara roasted in canola is a different meal than fries cooked in reused canola at a chain. Same oil category. Different exposure entirely.

What we see in client data

Across our coaching work and the 2,846-food dataset behind the meal plans, the clients whose inflammatory markers, body composition, and lipid panels improve are not the ones obsessing over which oil is in the bottle. They are the ones reducing ultra-processed food frequency, hitting protein targets, eating thirty-plus grams of fibre, training, and sleeping. Oil choice sits inside that, not above it.

We work alongside your GP on lipid panels and inflammatory markers. The pattern is consistent. Fix the diet pattern, and the oil question gets smaller.

What to do this week

  • Make olive oil your default. Keep one extra virgin for cold use, one standard for pan cooking.
  • Cut frequency of takeaway fried food before you stress about home cooking oils.
  • Store oils in a dark cupboard, not next to the stove. Replace any that smell rancid.
  • Audit your week for ultra-processed food share. That number moves health markers more than swapping oils.
  • If you want a marker-led answer, ask your GP for a fasting lipid panel and hs-CRP, then change one variable at a time.