Box lunch, as its name implies, is fast food, and some fast foods are not very hygienic, such as gutter oil and expired meat. Eating more fast food is not good for your health. Of course, the nutrition of fast food is also relatively low, and all the bodies can't absorb much nutrition. If you only insist on one box lunch a day, you may not lose weight obviously in a month, but if you do this for a long time, you will soon suffer from malnutrition, and then you will be sallow and emaciated.