Cooking
Applying heat to a food, which changes its structure, digestibility and nutritional value, with both beneficial and destructive effects depending on the nutrient and the method.
Cooking transforms a food on three levels: it destroys some of the micro-organisms, it changes the structure of molecules, and it changes taste and texture. Its nutritional balance is neither positive nor negative in itself: it depends on the nutrient in question and the method used.
It improves as much as it destroys. This is the point raw-food advocates gloss over. Cooking gelatinises starch and makes it digestible, denatures proteins so enzymes can break them down more easily, neutralises antinutrients (raw pulses are in fact toxic) and increases the availability of certain compounds such as the lycopene in tomatoes or the beta-carotene in carrots.
Conversely, it degrades the most fragile vitamins, first of all vitamin C and several B vitamins. Three factors weigh in: temperature, duration and above all contact with water, which carries water-soluble vitamins off into the cooking liquid.
High-temperature cooking raises a separate question: above about 120 °C, the Maillard reaction produces the desired aromas and colour, but also unwanted compounds such as acrylamide in heavily browned starchy foods. Hence the advice to cook to “golden” rather than “brown”. Gentle steaming, short cooking times and keeping the cooking juices remain the most worthwhile habits.