Fats are a diverse group of hydrocarbons and some are important in human nutrition. While fats are generally solid at room temperature, oils by contrast are liquid. Heating fats causes them to melt and become liquid and this can be seen during the cooking process when butter and lard both liquify upon heating. Cooking with oils is popular because it adds taste to the food and is an effective method of cooking.
When oils are heated they change chemically. In particular heated oils become oxidised and go rancid. When we eat these oils the rancid oils enter out metabolic pathways and interfere with normal metabolic regulation. Rancid oxidised oils are a primary driver of disease because they cause inflammation and oxidative stress. Such oils are now thought to be drivers of diseases such as cancer and cardiovascular disease, and may also contribute to obesity.
Fatty acids can be saturated, monounsaturated or polyunsaturated. While saturated fatty acids have no double bonds, monounsaturated and polyunsaturated fatty acid have one and more than one double bond respectively. Some polyunsaturated fatty acids such as fish oils can have 5 or 6 double bonds. The amount of double bonds in relevant to cooking, because the more bonds that are present on the fatty acid, the more likely it is to become oxidised and go rancid.
Most supermarket oils with the exception of extra virgin olive oil are deodorised and processed. During their extraction from the original seed, most of the vitamin E is extracted and sold, and the oil is deodorised by removing its phytonutrients to hide the original flavor. In this process the fatty acids become chemically altered through oxidation, and the end result is a disease causing oil. Cooking with such oils further oxidises the oil and creates a highly toxic food.
Extra Virgin Olive Oil
By law extra virgin olive oil must be extracted only with a mechanical press. This means that heat is not used in the process and the original content of the olives are left in the oil. Extra virgin olive oil therefore contains phytonutrients and vitamin E and this gives it healthy properties. However, when you cook with extra virgin olive oil, the oil oxidises and this creates an oxidised and rancid product that is disease forming.
Saturated fats are much more stable that the monounsaturated fatty acids in extra virgin olive oil. This means that when you heat them less damage is done to the oils. Saturated fats are therefore better cooking oils than vegetable oils that are monounsaturated or polyunsaturated. However as with all fats, heating them causes oxidation and will ultimately create toxic products and so care should be taken when using saturated fatty acids as with all fats.
Water Is The Solution
The solution is to cook in water. Where possible boiling foods will provide massive health benefits by eliminating a source of toxins. However, water does not have to be used exclusively to be of benefit. Adding a tablespoon of water to cooking fats will reduce the maximum temperature available to the pan and reduce the oxidation of the oil. This can provide the flavour of cooking with fats but the health benefits of cooking with water.