Which Cooking Oils Oxidize Fastest? An Oil Oxidizability Ranking
How is oxidizability measured?
By the Peroxidation Index (Witting & Horwitt, 1964): each fatty acid is weighted by how many bis-allylic weak spots it carries, so the score predicts how readily an oil oxidizes — in the bottle, in the pan, and in your cells.
The “seed oil” argument usually gets stuck on omega-6 ratios and shouting. The chemistry underneath it is simpler and far less arguable: some fats oxidize easily and some barely do at all, and the difference comes down to a single structural feature — the number of bis-allylic positions, the CH₂ groups wedged between two double bonds where a free radical strikes first.
The ranking below puts 24 common oils and fats on one scale. Sort by the Peroxidation Index, by total PUFA, by omega-3, by linoleic acid (LIN) — which reproduces the ordering of Table 1A in the book — or by smoke point; filter by category; and tap any oil to see its full fatty-acid breakdown and the data source. A few things jump out immediately.
Three things the ranking reveals
- The spread is enormous — over 70-fold. Flaxseed and fish oil sit at the top; coconut, butter, and beef tallow are near zero. These are not small differences.
- “Healthy” and “stable” are not the same axis. Omega-3-rich oils rank highest for oxidizability, because α-linolenic acid, EPA, and DHA carry the most weak spots. The index measures fragility, not virtue — omega-3s are essential; they are also the first to spoil.
- The cultivar matters more than the crop. High-oleic sunflower is one of the most stable liquid oils; ordinary high-linoleic sunflower is one of the least. Same plant, opposite ends of the chart.
Interactive Data · Lipid Peroxidation
Which cooking oils oxidize fastest?
The Peroxidation Index weights every fatty acid by how many vulnerable bis-allylic positions it carries — the exact weak spots a free radical attacks. Higher means more oxidizable, in the pan and in your cells. Tap any oil for its full breakdown.
Why a high score matters — and what to do about it
When a polyunsaturated fat oxidizes it does not simply “go off.” It fragments into reactive aldehydes that cross-link proteins and DNA and drive inflammation. That is the same chain reaction that ages cells, playing out in a frying pan. And it is why adding antioxidants only slows the spoilage rather than stopping it.
The structural fix is to protect the weak spots themselves. Replacing the vulnerable hydrogens with deuterium makes those exact bis-allylic positions far harder to attack — so a fat can keep its essential omega-3 chemistry while shedding its oxidative fragility. You can watch that trade-off happen in the chain-reaction simulator.
Snacking rather than cooking? The same index applied to 10 common nuts is in our nut oxidizability ranking, where walnuts top the chart and macadamias sit at the very bottom.
Method: Peroxidation Index = 0.025·MUFA + 1·LA + 2·ALA + 4·AA + 6·EPA + 8·DHA (Witting & Horwitt, 1964), where the coefficients track the number of bis-allylic positions per fatty acid. Composition data are representative averages of % total fatty acids from USDA FoodData Central (independently fact-checked); real samples vary by cultivar, refining, and season. A high index reflects oxidative fragility, not a judgment of nutritional value.
Want the full picture?
This article covers just one piece of the puzzle. The book connects all the dots: from the chemistry of aging to the deuterium approach.