Why is a balanced balanced diet important for a person?

1) Different foods contain different amounts of nutrients (proteins, fats, carbohydrates, vitamins, etc.), so the food should be varied.
2) The need for proteins, fats, carbohydrates in humans depends on age, gender, energy consumption, etc. For example, children need more protein for growth, less for older people. For a normal metabolism, it is necessary that the amount of energy supplied with food is equal to the cost of energy. Since proteins, fats, carbohydrates contain a different amount of energy, therefore, nutrition should be balanced in the content of these substances.