The first principle of a balanced diet is to match the main and secondary foods, there must be a suitable ratio between the main and secondary foods, if the main and secondary foods are reversed, it will cause an imbalance of nutrients, which will affect the health. The second principle of balanced diet is to match coarse and fine food in the main food, and coarse and fine food should also have a suitable ratio, otherwise if the main food is too fine or too coarse, it is not good for health. The third principle of a balanced diet is to match meat and vegetables in the side dishes, and the ratio of animal food to plant food should be appropriate, otherwise it may cause a high incidence of diseases due to excess fat.