Understanding the potential adverse effects of intermittent fasting is limited by an inadequate number of rigorous clinical trials. One 2015 review of low-quality clinical studies found that short-term intermittent fasting may produce minor adverse effects, such as continuous feelings of weakness and hunger, headaches, fainting, or dehydration. Long-term fasting may cause eating disorders or malnutrition, with increased susceptibility to infectious diseases.
Wesley Duewel, a twentieth-century writer, said, “You and I have no more right to omit fasting because we feel no special emotional prompting than we have a right to omit prayer, Bible reading, or assembling with God’s children for lack of some special emotional prompting. Fasting is just as biblical and normal a part of a spiritual walk of obedience with God as are these others.”
You'll probably lose weight on the Fast Diet because you’ll consume significantly fewer calories than you normally would on two days of the week. If you actually stick with the plan, you'll steadily drop weight. And because the two fast days are nonconsecutive and allow for at least some eating, the diet authors have found that people don't typically binge and overeat on the nonfasting days.
In section 106, of the same book, Yudhishthira says, "the disposition (of observing fasts) is seen in all orders of men including the very Mlechchhas..... What is the fruit that is earned in this world by the man that observes fasts?" Bheeshma replies that he had asked Angiras "the very same question that thou has asked me today." The illustrious Angiras says Brahmans and kshatriya should fast for three nights at a stretch is the maximum. A person who fasts on the eight and fourteenth day of the dark fortnight "becomes freed from maladies of all kinds and possessed of great energy."
While not yet proven in humans, early studies in rats seem to link intermittent fasting with increased longevity. One study found that intermittent fasting decreased body weight and increased the life span in rats (6). Another found that a group of mice who fasted intermittently actually lived longer than the control group, although they were heavier than the non-fasting mice. (7) Of course, it’s not clear that the same results would happen in humans, but the signs are encouraging.
Not only does fasting and prayer help us focus on God, but through that time, it brings us closer to Him and changes our hearts. Niles and Little write, "When we fast and pray, we are taking time away from a meal or an activity to devote our entire being to focus on God. We find we are more sensitive to the voice of God, more attuned to hearing what He has to reveal to us. Gently, God whispers in our mind what we were really thinking at the time of our sin, what our true intent was and we are shocked…momentarily. Then like a light turned on in a pitch black room, we see it. We did mean harm. We were manipulative. Even though our recognition makes us want to hide our face, our loving Savior lifts our chin to look into his forgiving eyes. As we repent, we no longer want to hide, but to praise and worship the very one who confronted our wrong."
In a physiological context, fasting may refer to the metabolic status of a person who has not eaten overnight, or to the metabolic state achieved after complete digestion and absorption of a meal. Several metabolic adjustments occur during fasting. Some diagnostic tests are used to determine a fasting state. For example, a person is assumed to be fasting once 8–12 hours have elapsed since the last meal. Metabolic changes of the fasting state begin after absorption of a meal (typically 3–5 hours after eating).