When heating oils at a high temperature (the temperatures used for deep frying), the structure of certain oils can change and create substances called aldehydes or lipid peroxides. These substances have been linked to an increased risk of heart disease and cancer.
So which oils form these harmful substances?
Oils such as sunflower oil, safflower oil and corn oil are high in polyunsaturates and despite often being thought of as the healthier choice, they form high amounts of aldehydes when heated to high temperatures. Fats high in saturates on the other hand like butter, lard, coconut oil and fats high in monounsaturates like olive oil or cold pressed rapeseed oil are much more stable and don’t produce these unhealthy substances. Therefore, these types of oils are better choices for frying at high temperatures.
Another tip to keep your fats at their healthiest, is to keep them away from the light and store them in a cool place to avoid any nasty substances forming. And for overall health, the best way to reduce intake of harmful aldehydes is to cut back on deep frying and lightly stir-fry, roast, grill or steam instead.
Written by Ruth Tongue