Health is defined by the World Health Organization as a state of complete physical, mental and social well-being, and not merely the absence of disease or infirmity. Building immunity and good defense is important for good health. The immune system is indeed a system, not a single entity.
Good nutrition is essential to a strong immune system, which offers protection not only from novel infections, such as COVID -19, but also seasonal illness, such as the flu and allergies, abnormal cell development and cancers. Energy intake should be as per requirement, since both over nutrition (obesity) and undernutrition can lead