Parla l'esperto: la cottura degli alimenti e la perdita di vitamine Ecosalute

The Expert Speaks: Cooking Food and Vitamin Loss

Dr. De Matteis , nutritionist biologist, explains how vitamins are destroyed with different cooking methods.

We often ask ourselves how to preserve vitamins and minerals when we start cooking vegetables.

The question is not trivial. What good would it be to consume cooked vegetables without assimilating the precious healthy contents? First rule, vegetables should never be left too long in water . Minerals and vitamins could dissolve and be lost forever.


When we peel the vegetables to remove the peel , we could lose a considerable part of nutrients more concentrated in the more peripheral parts. For example, the potato contains much more vitamin C in the peripheral area near the skin. The same goes for carrot, lettuce and spinach


Some vegetables can be eaten raw such as carrots , celery , fennel , etc. Others, on the other hand, in order to be consumed, must necessarily be cooked to soften the cellulose , a substance that is not easily assimilated by the human body. In fact , we do not have the cellulase enzyme that could break it down and make it more digestible. Herbivorous mammals such as ruminants, horses and rabbits, which do not produce this enzyme, have solved the problem by harboring bacteria in their stomach or intestines that are able to digest cellulose .

The cooking of vegetables serves to soften the cellulose in such a way as to facilitate digestion, using the two main cooking methods: in water and steam . Unfortunately, cooking in water results in a significant loss of nutrients . A good rule of thumb is to start cooking with already hot water , to allow the coagulation of the proteins present in the vegetables, even if present in small quantities.

Without this process, the escape of the juices from the plant cells would become more difficult. With cooking, albumin which is soluble in cold water but which coagulates with heat are lost in particular. Then some water- soluble vitamins such as C and B1 are also lost, and some saline compounds based on calcium and potassium . Vitamins are destroyed due to prolonged heat , for this reason cooking methods with short times are preferable. Vitamin C is destroyed at 60 °, those of group B and Vitamin E starting from 90 °.

Using cooking water is also a good method of recovering dissolved substances, at least those that were not destroyed by cooking.

Steam cooking can be used both in the traditional way and with the pressure cooker . With this method, contact with water is avoided and consequently the loss of nutrients is greatly reduced. If you want to preserve the aroma and flavor of vegetables, I recommend that you use the bain marie cooking for those that have a mild aroma, and the pressure cooker for those that have a stronger aroma such as cabbage.

General advice

  • Prepare the food without too much advance on cooking
  • Don't cut it any more than necessary
  • Don't cut leafy vegetables
  • Use stainless steel tools
  • Prefer stainless steel or pyrex containers
  • Add the vegetables only when the water has started to boil
  • Do not exceed with the amount of water
  • Turn off the heat as soon as the vegetables are cooked

  • Cooking cereals

Whole grains , before cooking them, should be soaked in cold water , as the water allows you to eliminate phytates , substances that counteract the absorption of minerals such as iron , zinc and vitamins by the intestine .

  • Cooking the fish

To avoid losing protein substances , it is good to cook fish in the oven , on the grill or on the grill. In any case, good quantities of B vitamins will be lost. An excellent cooking method to avoid the loss of vitamins is that in foil .

  • Cooking the meat

By cooking the meat, it becomes more tender , chewable and digestible. Unfortunately, vitamins and mineral salts are also lost , except in the case in which the external crust forms which retains the precious nutrients inside the meat. Avoid cooking methods such as braising and stewing which among other things make the meat less digestible.

  • The frying

With frying , foods are cooked at temperatures above 180 ° . With this method, a crunchy outer crust is formed which also limits the absorption of the oil used for frying and the food remains soft. The ideal thing would be to be able to keep the temperature of the oil below the point where it starts to smoke , to maintain a good part of the nutritional values. The type of fat used also counts for a lot.

The best oil is extra virgin olive oil , low in saturated fatty acids and rich in antioxidants . Peanut oil has good stability at high temperatures but unfortunately it is rich in saturated fatty acids, the bad ones so to speak. Same goes for lard, lard and coconut. Butter , soy , sunflower and corn easily degrade at high temperatures, so it's best to use them raw . As for air frying , a modern method, we can say that it is a dietary method but unhealthy as substances harmful to health could be formed, due to foods subjected to too high temperatures.

  • Baking

During cooking in the oven, a dry heat is released which varies from 130 to 250 degrees. Compared to boiling and frying, it is a slower system that has the advantage of obtaining a more uniform cooking than frying , with minimal loss of nutrients, especially if they use methods such as cooking meat in foil or salting fish.

  • Microwave cooking

With this method, a food similar to that derived from boiling is obtained, but since there is no water, the nutrients remain in the food .


Palermo M et al. '' The effect of cooking on the phytochemical content of vegetables ''. J. Sci Food Agric. 2014 Apr; 94 (6): 1057-70.


Author: Dr. Giuseppe De Matteis, Nutritionist Biologist