Fasting is not just the state of remaining hungry and thirsty. If an animal or a disbeliever is confined in a room and deprived of food and water, this is not considered fasting. In fact, fasting has a connection with other acts of worship, such as patience, giving thanks to Allahu ta'ala, and disciplining the nafs. Therefore, it is stated in a hadith-i sharif, "Everything has a gate. The gate of worship is fasting" (Ibn Mubarak).
The nervous system has a vital place in the human body. Those whose lingual nerves have been paralyzed cannot talk. Those whose nerves in their legs have been paralyzed cannot walk. Our lives are in danger to a lesser or greater degree as per the nervous system disorder we experience. People who suffer from neurosis are restless and impatient. Most of the fights and murders that occur within the community spring from being nervous and lacking patience. The hadith-i sharif, "Fasting is half of patience, and patience is half of faith," states that a fasting person is forbearing. (Abu Nu'aym)
Thus, it is seen that fasting is also from faith. Those who have faith do not commit crimes or sins in accordance with the strength of their faith. They keep their temper. There is a zakat for everything, and the zakat of the body is hunger. Because the desires of those who remain hungry by fasting are restrained, it is easy for them to show patience. Fasting people remain hungry. Remaining hungry, in turn, is beneficial: It develops one's insight (basirah) and enhances one's ability to understand. As a matter of fact, it was declared in hadith-i sharifs, "The comprehension of a hungry person increases, and his intellect is sharpened" and "Meditation [tafakkur] is half of worship, while eating little is all of it" (Imam-i Ghazali).
Those who eat much sleep much, thus spending their lives doing nothing. They are like drunks. Their brains become sluggish, and their intellects and memories atrophy. However, hunger brings tenderness to the heart. A hadith-i sharif says, "The interior of a person who eats little is filled with lights. Allahu ta'ala loves the Believer who eats and drinks little and whose body is light in weight" (Daylami).
In a state of hunger, desires are curbed. Leaving disobedience, our nafses become submissive. On the other hand, overeating causes negligence. Just as it is difficult to subjugate a wild horse, so it is difficult to subjugate the nafs that had gotten out of hand as a result of overindulgence in food. Hunger facilitates training of the nafs. It was declared in a hadith-i sharif:
(The human heart is like crops in a field, and eating is like rain. Just as excessive rain causes crops to rot, so excessive food causes the heart to die.) [Imam-i Ghazali]
Those who are always full up become merciless and ruthless. They cannot imagine what it means to be hungry. Gluttonous people become hard-hearted. It was related in a hadith-i sharif, "Do not kill your heart by eating and drinking much" (Imam-i Ghazali).
Those who keep their temper experience inner happiness. Hunger crushes one's hankering to commit sins and prevents one from doing evil deeds. A hadith-i sharif says, "Fighting against the nafs through hunger and thirst is like fighting in the way of Allah" (Imam-i Ghazali).
Those who eat much drink much water. Those who drink much water, in turn, sleep much. Since such people spend their lives sleeping, this state keeps them from earning material and spiritual profits. This means to say that hunger keeps nerves agile and energetic. Repletion results in imbecility. It inhibits memorization and keeping something in mind. A hadith-i sharif says, "Eating a meal once a day is moderation" (Bayhaqi).
Having meals three times every two days [that is, morning and evening meals on the first day and lunch on the second day] was reported to be standard. (Tashil-ul-manafi)
Most of diseases result from eating much. It was stated in a hadith-i sharif, "Eating and drinking much is the source of diseases" (Dara Qutni).
Those who eat little will have healthy bodies. "He who fasts will have a good health," was said in a hadith-i sharif. (Tabarani)
The feeling of pity in those who consume excessively will lessen. Their sensual desires will increase, and they will engage in forbidden deeds. It is necessary to block off all the paths that excite unlawful desires. Hunger, in this respect, blocks off Satan's path. A hadith-i sharif declares, "Satan circulates in the body like blood. Make his passage narrow by means of hunger" (Ihya).