All preparation and cooking activities can alter the composition of foods in terms
of their nutrients: not all, however, negatively impact on their nutritional qualities.
Proteins, for example, tend to undergo denaturation, losing their intricate, globular
structure and expanding and becoming easier to digest as a result.
Other substances with antioxidant properties, such as lycopene, found mainly in tomatoes, become more bioavailable when cooked, i.e. easier for our bodies to use.
The most sensitive nutrients to cooking and preparation activities are vitamins, especially water-soluble vitamins and those from groups B and C in particular. The loss of these substances during regular cooking activities - but also, for example, in the reheating of already-cooked foods - is quite significant, coming to around 50% in the case of vitamin C and as much as 70% for folates.
Fat-soluble vitamins such as vitamins A, D, E and K are more resistant (percentage loss of around 25%) as are mineral salts, which to a minor degree tend to dissolve in cooking liquids; these range from a 20% loss in the case of calcium, to 25% for magnesium and 40% for copper.
There is no need to fear though. The right balance of raw and cooked foods in our diet guarantees all the nutrients that we need without exposing us to the risk of deficiencies and, above all, without requiring us to take vitamin and mineral supplements which, if not properly evaluated by healthcare professionals, can be both pointless and counterproductive.