When any fats or oils are heated to temperatures of 350 to 400 degrees F
(177 to 204 degrees C), their smoke points often are exceeded, allowing
mutagenic products of oxidation to form. It’s safest to avoid deep-fried foods
and minimize the use of oils when cooking over high heat.
Generally, refined oils are more heat stable than unrefined oils, because they
contain fewer of the solid particles that burn easily. However, the refining
process itself can damage fat molecules, and it removes most of the protective
components associated with the whole food. Unrefined oils (which can be a
source of healthful fats when properly stored) have smoke points as low as 200
to 225 degrees F (93 to 107 degrees C); they’re best reserved for salads and
other unheated foods.