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5 Leftover vegetables are not edible, because they have a lot of poisonous nitrites.

Professor Fan Zhihong of the China Agricultural University once did an experiment on this question. She put cooked vegetables in a refrigerator, and 24 hours later, quantity of nitrites in the vegetables almost doubled, from 300 milligrams per kilograms to 700 milligrams. However, despite the increase, she pointed out that a person needs to eat almost 30 kilograms of vegetables in order to get poisoned by the nitrites in the food.

Vegetables have nitrites, but differ in amount. Cucumbers, beans and tomatoes usually have a low level of nitrites. We suggest people not cook too many vegetables in order to avoid leftovers, and to put the some of the cooked vegetables in the refrigerator as soon as they are cooked.