We often hear that cooking destroys the nutritive value of food; but is it really true? Recent research has shown that this is primarily true for 2 vitamins namely vitamin B & C. These are the two most heat-labile (i.e. destroyed or altered by heat) nutrients and prolonged heating breaks down their structure. However, most of other nutrients are not affected adversely by any cooking method.
Researchers say that cooking infact improves the digestibility of most of the proteins and fibers. Some cooking methods also help in the preservation of food items by making them less susceptible to spoilage.
However, certain cooking methods such as frying, sautéing, deep frying etc. may be unhealthy as these add fat and calories to foods. So even though the nutrient content of the food is not affected, such cooking options can certainly make the food high in calories. Half of the calories in fried food items come from the oil it is cooked in.
The researchers therefore, conclude that although certain cooking methods could affect the calorie content of the food, they usually do not decrease the nutritional value of that food.