Bible Study on Fasting
The Bible, including Jesus, talks about fasting as a normal spiritual exercise. The Bible may not mandate it, but fasting clearly is considered a means of greater spiritual proximity to God / receptivity of God to answer prayer, because fasting is an act of humility or demonstrates an earnestness that impresses God, etc. Here are passages to consider:
Howbeit this kind goeth not out but by prayer and fasting. (Matthew 17:21)
Now in the twenty and fourth day of this month the children of Israel were assembled with fasting, and with sackclothes, and earth upon them. (Nehemiah 9:1)
And in every province, whithersoever the king's commandment and his decree came, [there was] great mourning among the Jews, and fasting, and weeping, and wailing; and many lay in sackcloth and ashes. (Esther 4:3)
But as for me, when they were sick, my clothing [was] sackcloth: I humbled my soul with fasting; and my prayer returned into mine own bosom. (Psalms 35:13)
When I wept, [and chastened] my soul with fasting, that was to my reproach. (Psalms 69:10)
My knees are weak through fasting; and my flesh faileth of fatness. (Psalms 109:24)
Therefore also now, saith the LORD, turn ye [even] to me with all your heart, and with fasting, and with weeping, and with mourning: (Joel 2:12)
My Spiritual Experience Proves Physical Benefits Too
I have recently tried fasting once a week, and tie it to a spiritual purpose -- to learn not to give into the flesh' desire for food. I am overweight by 12 pounds. So there is a bit of "gluttony" I wish to conquer. [Update: 2014 - I went from 190 lbs to 156 lbs. I was overweight more than I thought.] I have found that fasting directly aids my diet, and indeed makes it easier during the week to resist eating too much. So I have learned that fasting periodically has improved my physical and spiritual health. Perhaps give that a try.
But I understand that for reasons I do not yet understand, one is not supposed to fast on Sabbath. We read in "Eve of Passover," Wikipedia: "This is because it is forbidden to fast on Shabbat (except when Yom Kippur falls on Shabbat)...."
Health Benefits of Fasting
Incidentally, a June 2014 study shows that fasting for at least 3 days resets your immune system, thereby repairing it. Here is an article that appeared in the Daily Mail. On a thorough review of all health benefits of intermittent fasting, see Jen's Review The Ultimate Guide to Intermittent Fasting.
Incidentally, Jen's Review has an interesting article on the health benefits of Parsley, with links to the science. The review interestingly suggests drinking tea with parsley, which has a diuretic effect, thus cleansing your kidneys. I eat Parsley fresh off my TowerGarden every day. Glad to know the benefits. I am also crazy for Lentils, and Jen's Review has an article on the 15 Health Benefits of Lentils.