Vitamins are acaloric nutrients, that is, our bodies cannot derive energy from vitamins introduced in food. The fact that they do not add to energy levels does not mean that they are not important: on the contrary, they are paramount to maintaining a healthy metabolism and working bodily functions.
Vitamins are not only found in plant-based foods. Vitamins are found in all foods, but obviously each food has different amounts of certain vitamins. For example, vitamin C can only be found in plant-based foods, and vitamin B12 in animal source foods. A deficiency of vitamin B12 is the main challenge of a vegan diet which, since it does not include animal source foods, does not contain it, and it is therefore necessary that it be taken through a supplement.
The amount of vitamins found in foods also varies depending on whether it is consumed raw or cooked, because most vitamins are sensitive to heat and some will be destroyed during cooking, both industrial and home cooking. Contrary to what is commonly believed, sometimes industrial cooking reduces the content of vitamins less than when it is done at home because food is cooked at controlled temperatures and for shorter times. At home, you should be careful not to “overcook” food to prevent the loss of vitamins as much as possible.
Of course, the way a food is cooked also has an effect: cooking by immersion in water (simmering and boiling) generally lead to the most vitamin loss, due to dispersion in the cooking water itself.
Several studies have shown that freezing food has very little effect on its vitamin content. Even with frozen food, just as with fresh, the problem tends to be linked to the cooking that comes next.
The vitamin requirements vary among different ages, but normally it is thought that a balanced and varied diet, which incorporates all the food categories and includes the five recommended daily portions of fruit and vegetables, is able to provide the correct amount of vitamins for adults and children. For nutritional imbalances and particular periods of life which necessitate a higher intake of certain vitamins (for example during pregnancy), supplements can be taken, but they should not be thought of as dietary substitutes, but as a complementary method to meet the levels of vitamins required. So, if a child does not eat fruit and vegetables, simply making them eat them will not solve the problem, they must be taught to make healthy food choices consistently.

Alessandra Bordoni
Department of Agricultural and Food Sciences
University of Bologna