It is best to eat in kind on the same day, because some overnight vegetables, especially overnight green leafy vegetables, not only have low nutritional value, but also produce pathogenic nitrite. The production of nitrite in stored vegetables increased with the increase of storage time and temperature. Vegetables are stored in the refrigerator (2-6 degrees Celsius), and nitrite increases less. Therefore, if it's winter, some families think it's cold and leftovers don't need to be put in the refrigerator. In fact, this view is also wrong. However, putting vegetables in the refrigerator does not mean that you can rest assured; After a long time, the content of nitrite will still increase, so it is recommended to eat it as soon as possible. It is worth mentioning that different kinds of vegetables produce different amounts of nitrite under the same storage conditions. Usually, stem and leaf vegetables are the highest, melon vegetables are slightly lower, and roots and cauliflower are in the middle. Therefore, if you buy different kinds of vegetables at the same time, you should eat stems and leaves first, such as Chinese cabbage and spinach. If you are going to cook more vegetables and eat them hot the next day, try to make fewer stem and leaf vegetables and choose melons. And there is oil and salt in the fried dishes. After a night, the vitamins in vegetables were oxidized, and the content of nitrite increased greatly, which became nitrite after entering the stomach. Although nitrate is not a direct carcinogen, it is very harmful to health. When nitrite enters the stomach, it will produce a substance called NC(N- nitroso compound) under certain conditions, which is one of the risk factors of gastric cancer. Especially in hot weather, overnight meals are contaminated by bacteria, which will multiply in large numbers and easily lead to gastroenteritis and food poisoning. Many fried dishes can't be eaten and stored, especially some high-protein and high-fat leftovers. The harmful bacteria in the air will attach to the leftovers within 2 hours and start to multiply. As we all know, most protein and fat will produce harmful substances under the action of bacteria, such as hydrogen sulfide, amines, phenols and so on. It is harmful to human body. It is an indisputable fact that eating leftovers for a long time is easy to cause cancer. Therefore, you can't eat overnight dishes. When cooking, the best way is to tailor your clothes, not to harm your health!