First of all, chemicals in food can produce carcinogens, such as nitrite, which cannot be removed even by heating.

Another reason is the secondary pollution caused by foreign bacteria when placed. Usually, the nitrate content of stem and leaf vegetables is the highest, while that of melon vegetables is slightly lower, and roots and cauliflower are in the middle. Seafood such as crab, fish and shrimp will produce protein degradation products overnight, which will damage the function of liver and kidney.

Extended data

1. Never drink overnight tea.

After staying overnight for a long time, most of the vitamins are lost, and the protein and sugar in the tea soup will become nutrients for bacteria and mold. So people usually think that overnight tea can't be drunk.

2, the rotten pot-stewed food at home is not overnight.

Don't eat bad pot-stewed vegetables overnight in spring and summer. Bulk braised pork should be eaten on the same day, not overnight. Food experts warn that even the food in the refrigerator is not absolutely "safe". Refrigerators are prone to mold and psychrophilic bacteria. If possible, it is best not to eat bad goods overnight.

People's Daily Online-Eight kinds of overnight dishes will be poisoned. How to deal with them without wasting them?