When you cook with certain plant oils like sunflower or soybean oil, even at normal cooking temps that aren’t hot enough to make them smoke, they can break down into harmful chemicals — and if you heat them for 30 minutes straight, those harmful chemicals become ten times more toxic.
Evidence from Studies
Supporting (4)
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The study heated cooking oils like sunflower and rapeseed at normal frying temps and found they turned into harmful chemicals over time—exactly what the claim says, even if it didn’t measure the exact 10x increase.
Oxidative Stability and Genotoxic Activity of Vegetable Oils Subjected to Accelerated Oxidation and Cooking Conditions
The study heated seed oils like rapeseed and grape seed oil at frying temperatures and found they produced a lot of harmful chemicals called aldehydes—exactly what the claim says. Even though it didn’t test exactly 30 minutes, the results still back up the main idea.
Toxic aldehyde generation in and food uptake from culinary oils during frying practices: peroxidative resistance of a monounsaturate-rich algae oil
The study found that common seed oils like sunflower oil turn into harmful chemicals when heated for a long time while frying, which matches the claim. The more you heat them, the more bad stuff forms.
This study says that oils with lots of polyunsaturated fats (like seed oils) break down into harmful chemicals when heated for a long time while frying — which matches the claim that these oils turn toxic when cooked, even before they start smoking.
Contradicting (0)
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Gold Standard Evidence Needed
According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.