Answered by Sayyidi Habib Umar bin Hafiz (may Allah protect him and benefit us by him).
The teachings of Islam encourage us to reduce our food intake but medical experts say that doing this weakens one’s immune system. How do we respond to this?
Reducing one’s food intake may weaken the immune system if it is done suddenly without giving the body the nourishment that it requires. If, however, it is done gradually while giving the body the nourishment that it requires it improves one’s health and strengthens the immune system.
Experience shows that those who have strived to lessen their food have been the healthiest people.