The idea of giving up food is a wrong inspiration. You can go on with a small quantity of food, but not without food altogether, except for a comparatively short time. Remember what the Gita says, “Yoga is not for one who eats in excess nor for one who abstains from eating altogether.” Vital energy is one thing—of that one can draw a great amount without food and often it increases with fasting; but physical substance, without which life loses its support, is of a different order.
Ref : Letters on Yoga Vol. IV