Great importance has been attached to the healthy diet in recent years. It is not suggested for people to eat much at supper. This causes a new problem. Sometimes, there would be leftovers. How can we deal with food of the previous day? Does it become unhealthy or harmful? Experts tell us that most food of the previous day is not good. 

First of all, do not water of the previous day. Western people tend to drink cold water, while eastern people have the habit of drinking warm water. Experts find that water which is boiled for three to five minutes is most suitable for drinking because the content of nitrite and chloride is lowest at this time. If water is boiled for a long time, or boiled water has been put for over 24 hours, the content of nitrite will increase by 30%. As we know, nitrite would produce nitrosamine in the human body and lead to cancer. Therefore, keep away from water of the previous day.

Secondly, tea can not be left to the second day. The vitamins in tea leaves would disappear overnight. What is worse, the protein and sugar in tea would become food for bacteria. Overnight tea would make people ill.

Thirdly, overnight eggs are not all dangerous. After research, scientists has made such a conclusion that fully cooked eggs are safe to eat. Eggs that are not completely cooked would bring bacteria overnight and cause discomfort of intestines and stomachaches. But when they are deeply cooked and kept in cold places, they are still safe enough.

Fourthly, overnight vegetables are harmful. Some vegetables, such as cabbage and spinach, are rich in nitrate. If they stay overnight, the nitrate would be decomposed and produce nitrite, which may easily cause cancers. If you prepare too many vegetables, please eat those with leaves first. The leaves would turn yellow. Sometimes, the flavor of the dishes would change to some extent.

Fifthly, seafood of the previous night does harms to the health of human beings. Seafood, including fish and shrimps, would be less nutritious if it is put overnight. Certain substances in it would decompose protein and release some chemicals that hurt lungs livers and destroy the functions of kidneys.

Lastly, overnight tremella soup can not be eaten. Tremella is a kind of high quality nutriment. The valuable ingredients would reduce, while some harmful chemicals will appear, if it is placed for one night. There is a large amount of nitrate existing in tremella. When it is cooked and put for a long time in the air, the nitrate would be deoxidized and become nitrite again. When people drink such overnight soup, the nitrous acid naturally enters the human body and participates in the blood circulation. In consequence, the normal erythrocytes in blood are oxidized and lose the ability of transmitting oxygen.