Physical advantages of fasting

The learned scholars of moral ethics have described numerous advantages for hunger, some of them will be mentioned here as follows:

1. One of the effect of less eating is purity of heart and insight, because, over-eating and fullness creates a state similar to drunkenness within a human being which slows down his sense of perception, reducing his power of quick grasping, thus, ultimately resulting in his heart's blindness. Opposite to that, hunger results in the mind becoming sharp, bestows comprehension upon conscience, thus, making the heart readied for enlightenment. In this regard the following tradition has been narrated from the Holy Prophet [s]:
   "Whoever keeps his stomach hungry his thinking culminates to the highest level, thus, making his reflections stronger."
2. The other effects of less eating are humility, hospitality, self-breaking, earthiness, and freedom from arrogance, egotism, and haughtiness, because these are the by-products of transgression, rebellion, and ill-servitude towards Allah (the Glorious, the Exalted). The one who frees himself from these calamities through hunger will also make himself readied for humility, obedience, and surrender before the Lord.
3. The other effects of less eating are lowering of intensity of sensual passions and other such motivations which invite a human being towards sinning and other deviations. As we know in most of the cases sins and transgressions are committed as a result of passionate talks and other sensual motivations, therefore, controlling these passions through hunger might free us from getting entrapped into many dangerous situations.
4. Another effect of less eating is less sleeping, we know that oversleeping is one of the most important factor of wasting of our age which is the precious sum at our disposal for our hereafter's affairs. But hunger reduces sleep, thus, providing opportunities for night vigil, the source of all blessings and bounties, and helps a human being in worshipping and supplications which is the ladder for his attaining the most desirable spiritual station (Maqam-e-Mahmud).
5. Another effect of less eating is the ease of worshipping rather servitude, because, the one who is used to less eating will save a lot of time which otherwise must have been spent for making arrangements, purchasing, cooking, consuming, and relieving, as well as time spent for medical treatment, since in many cases the sickness is the cause of over-eating. Therefore, he will utilize all this available time in worship and servitude; in addition to that he will free himself from the hardships of arranging good foods and medical treatments, which means that he will be having more free time as well as more ease and comfort.
6. Another effect of less eating is the financial ability of a person to spend for charity, benevolence, pilgrimage, and other acts of worship which require expenses, because, a lot of expenses spent only for providing unnecessary food items or for medical treatment as a result of over-eating, could be utilized for the above-mentioned worships. The advantages described are so vast in scope that the faculty of reason is helpless to describe their profundities.
7. Especially, the prime advantages are purity of heart, sharpness of mind and thinking, because, thinking is tantamount to ultimate result while our other actions and deeds are tantamount to preliminaries. Even thinking or meditating in itself is spiritual journey while the other actions and deeds constitute the preliminaries and background of this spiritual journey. It is in this background that the narration says:
   "Meditating for even a single second is better than worshipping for seventy years."

Ref: Spiritual journey of the mystics