Question: Is fasting harmful to the body?
No, it is not harmful because Allahu ta'ala does not order us to do what is harmful. Medical specialists say the following about this topic:
In the bodies of fasting people, epinephrine and cortisone hormones mix into the bloodstream more easily. These hormones have effects also on cancerous cells. They serve as a shield against cancer; that is, they prevent the growth of cancer cells. Indeed, the body of a fasting person is in maintenance mode. The fat that surrounds internal organs melts away. The body becomes invigorated and gathers physical strength with an increased level of resistance to diabetes as well as stomach, kidney, heart, and liver diseases.
The liver takes a rest for 3-5 hours during fasting, thereby stopping storage of food substances for a while. In the mean time, it prepares globulins, which will boost the immune system. Muscles in the stomach and cells that release secretions, too, have a rest for some time during fasting hours. As the volume of blood circulating in the body decreases and consequently blood pressure drops, the heart relaxes.
If waste materials from food are not burned thoroughly, they impair arteries. Unburned fats make arteries narrower and cause the disease called arteriosclerosis. [During the practice of fasting], nearly no substance is left in the body towards sunset. That is, all substances are metabolized. Hence, fasting is beneficial for some diseases, especially for arteriosclerosis sufferers. Other body organs, too, get a chance to rest. Eating less and fasting are of vital importance for body health. Zakat (obligatory charity) is the dirt of wealth. Just as a zakat giver protects his/her wealth against dirt, so a fasting person pays the zakat of his/her body and protects it against diseases. Our master the Prophet said, "There is a zakat for everything. The zakat for the body is fasting" (Ibn Maja).
Benefits of fasting are many. Two hadith-i sharifs say:
(Fasting melts away the flesh and keeps a person away from Hellfire. The blessings that no eye has ever seen, no ear has ever heard, and no mind has ever imagined will fall only to the lot of a fasting person.) [Tabarani]
(Whoever observes fast for a day in the way of Allah, Allahu ta'ala, owing to this single fast, keeps him seventy years' distance away from Hell.) [Bukhari]
The reward for fasting is much more compared with other acts of worship. It was declared in a hadith-i qudsi, "Each good deed is rewarded from tenfold to seven hundredfold. However, fasting is for Me, and it is I who will reward it because My servant has abandoned his lust and his eating and drinking for Me" (Bukhari).
Though it is Allahu ta'ala who gives reward for each good deed, there is a divine reason for His saying, "It is I who will reward it." Even though the whole globe is in Allahu ta'ala's possession, the Kaaba is called Baitullah (the House of Allah) in order to honor it. By saying, "Fasting is for Me," He grants it a special honor. The reward (thawab) that will be granted to the fast observers is beyond measure. Much thawab will be given to them in accordance with their states. It is more rewarding to fast when others do not. A hadith-i sharif says, "When those who do not fast eat near a fast observer, angels pray for him" (Tirmidhi).
Those who cannot observe voluntary fast for any reason whatsoever should render thanks to Allahu ta'ala and feed guests and the poor. It was declared in a hadith-i sharif, "He who feeds others by giving thanks is like the one who fasts by showing patience" (Tirmidhi).
The thankful people will be rewarded abundantly. To be thankful (shukr) means to live by Islam.
Hadrat Imam-i Rabbani states, "The rewards given for the voluntary worships done in Ramadan are like those given for the obligatory ones done in other months. One obligatory act of worship done in this month is like seventy obligatory acts of worship done in other months. If a person disrespects this month and commits sins during it, he/she will spend all the year sinning."
Therefore, we must more strictly avoid sinning especially in the month of Ramadan. Additionally, acts of worship performed at holy places are more rewarding. As a matter of fact, a hadith-i sharif says, "One Ramadan fast observed in Mecca is more meritorious than a thousand Ramadan fasts observed in another place" (Bazzar).
In a similar way, the reward for acts of worship offered on Friday is multiplied, and sins committed on Friday are registered twofold. We should appreciate the value of sacred days and behave accordingly.