One reason experts tell people not to cut way back on calories is that it can slow your metabolism, making it even harder to lose weight. But studies show that fasting from time to time can be an effective strategy for weight loss. In addition, cutting calories on a couple of days instead of every day may help preserve muscle, so you lose mostly fat.
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."
Physiologically, calorie restriction has been shown in animals to increase lifespan and improve tolerance to various metabolic stresses in the body.  Although the evidence for caloric restriction in animal studies is strong, there is less convincing evidence in human studies. Proponents of the diet believe that the stress of intermittent fasting causes an immune response that repairs cells and produces positive metabolic changes (reduction in triglycerides, LDL cholesterol, blood pressure, weight, fat mass, blood glucose). [3,5] An understandable concern of this diet is that followers will overeat on non-fasting days to compensate for calories lost during fasting. However, studies have not shown this to be true when compared with other weight loss methods. 
The main benefit of intermittent fasting is weight loss—fat loss, specifically. “Insulin increases when you eat, and when insulin is high, you cannot burn fat. When you fast, insulin falls, which allows your body to access its stores of food (i.e., body fat) for energy,” explains Jason Fung, M.D., a Toronto-based nephrologist and author of The Complete Guide to Fasting.
John Calvin, the figurehead of the Reformed tradition (the Continental Reformed, Congregational, Presbyterian, and Anglican Churches) held that communal fasts "would help assuage the wrath of God, thus combating the ravages of plague, famine and war." In additional, individual fasting was beneficial in that "in preparing the individual privately for prayer, as well as promoting humility, the confession of guilt, gratitude for God's grace and, of course, discipling lust." As such, many of the Churches in the Reformed tradition retained the Lenten fast in its entirety. The Reformed Church in America describes the first day of Lent, Ash Wednesday, as a day "focused on prayer, fasting, and repentance" and considers fasting a focus of the whole Lenten season, as demonstrated in the "Invitation to Observe a Lenten Discipline", found in the Reformed liturgy for the Ash Wednesday service, which is read by the presider:
Dr. Michael Mosley popularized this variation of intermittent fasting in his book ‘The Fast Diet’. This involves 5 regular eating days and 2 fasting days. However, on these two fasting days, it is permitted to eat 500 calories on each day. These calories can be consumed at any time during the day – either spread throughout the day, or as a single meal.
You can theoretically eat whatever you want when you're on an IF plan (and not in the fasting phase), but if you overdo the carbs, you'll have trouble keeping your blood sugar stable. Refined carbs, in particular, make your blood sugar rise and your insulin spike and crash. So if you're trying to go without food for longer periods and your diet is too carb-heavy, you're going to end up pretty hungry and irritable.
Fasting also appears as a sign of mourning. Following Saul's death, the people of Jabesh- Gilead lamented his passing by fasting ( 1 Sam 31:13 ) as did David and his companions when they heard the news ( 2 Sam 1:12 ). David goes so far as to say that he commiserated with his enemies when they were sick, fasting and dressing himself in sackcloth ( Psalm 35:13 ). Such behavior was a sign of his mourning over them (v. 14). Zechariah describes the commemoration of Israel's tragic days of past defeat and judgment as times of mourning attended by fasting ( 7:5 ). But these days of fasting in the fourth, fifth, seventh, and tenth months will one day be turned to times of joy ( 8:19 ). Jesus speaks of the time of his departure from his disciples as a time of mourning when it will be entirely appropriate to fast ( Matt 9:14-15 ; Mark 2:18-20 ; Luke 5:33-35 ).
So wrong and inaccurate in so many levels I really don’t know where to start in trying to correct such an ignorant statement. I don’t know if you are being sarcastic in this post… 1st of all it is not ‘simple’ in any way to avoid bad foods-our primitive brain cries out for them and when we diet it cries out louder. That is the big reason dieting is soo hard to stick to, it’s putting the body and mind under very unnatural conditions.
Tisha B'Av and Yom Kippur are the major fasts and are observed from sunset to the following day's dusk. The remaining four fasts are considered minor and optional fasting is only observed from sunrise to dusk. Both men and women can choose to observe them, and a rabbi may give a dispensation if the fast represents too much of a hardship to a sick or weak person, or pregnant or nursing woman.
On its web site, the Academy of Nutrition and Dietetics says that although there is evidence that intermittent fasting diets may help prevent chronic disease, more research is needed. It doesn't recommend the diet because "it is not a realistic long-term solution.” The academy also notes that "any variation of fasting may make a person irritable, cause daytime sleepiness/sleeplessness at night, and can even lead to dehydration."
This proved to be the most important forty days of my life. As I waited upon the Lord, the Holy Spirit gave me the assurance that America and much of the world will, before the end of the year 2000, experience a great spiritual awakening. This divine visit from heaven will kindle the greatest spiritual harvest in the history of the Church. But before God comes in revival power, the Holy Spirit will call millions of God's people to repent, fast, and pray in the spirit of 2 Chronicles 7:14:
Fasting sounds so simple, and yet the world, our flesh, and the devil conspire to introduce all sorts of complications that keep it from happening. In view of helping you start down the slow path to good fasting, here are six simple pieces of advice. These suggestions might seem pedantic, but the hope is that such basic counsel can serve those who are new at fasting or have never seriously tried it.
I sometimes hear people say, "I'm giving up chocolate" and they regard this as a type of fasting. I think this is a rather frivolous approach. The first and foremost purpose of a biblical or spiritual fast is to get a breakthrough on a particular matter that one lifts up to the Lord in prayer. A spiritual fast involves our hearts and the way in which we relate to and trust God. It relates to discerning and receiving strength to follow through on what God might reveal to us about circumstances in our lives or a direction we are to take.
Through the years, I have learned that many people in the church have never been taught about fasting and prayer, and many have therefore never fasted and prayed. As a result, they don't know why fasting and praying are important, what the Bible teaches about fasting, or how to fast. To many, fasting sounds like drudgery -- or a form of religious works. To others, fasting sounds extremely difficult. People tend to stand in awe at reports of those who have fasted for several weeks. When I hear about such fasts, I no doubt think what they think: If I fasted that long, I'd die! I couldn't possibly do that!
As I began my fast, I was not sure I could continue for forty days. But my confidence was in the Lord to help me. Each day His presence encouraged me to continue. The longer I fasted, the more I sensed the presence of the Lord. The Holy Spirit refreshed my soul and spirit, and I experienced the joy of the Lord as seldom before. Biblical truths leaped at me from the pages of God's Word. My faith soared as I humbled myself and cried out to God and rejoiced in His presence.
But here’s something important to note about what we know from science about fasting: Though a lot of the popular interest is in weight loss, many of the key researchers who study fasting aren’t focusing on that at all. In fact, many of the studies on fasting come from institutes of aging, like this one, and the researchers behind the studies actually focus on longevity and disease prevention.
Now there's certainly an issue of food that is associated with many seasons of prayer and fasting, and let me quickly add this: control of eating is a valid reason to fast. The purpose is not the number of pounds you might lose during a fast, but rather, trusting God to help you regain mastery over food during a fast. Jesus said, "The spirit is . . . willing, but the flesh is weak" (Matt. 26:41). Fasting is a means of bringing the flesh into submission to the Lord so He can strengthen us in our mastery over our own selves. Fasting in the flesh makes us stronger to stand against the temptations of the flesh. Those temptations very often deal with food.
If you're worried you’ll be starving while fasting, you’ll be pleasantly surprised! Intermittent fasting decreases your hunger hormone ghrelin, which in turn can increase dopamine levels in the brain. (Just another example of the gut-brain axis at work.) Fasting can also help free people from emotional eating and kill cravings by transitioning your metabolism from unstable sugar-burning to steady fat-burning.
“Cycles of fasting can reset and rejuvenate the human body,” said Valter Longo, director of the Longevity Institute at the University of Southern California. Periods with no food, he said, help the body eliminate and replace damaged cells with new ones through a process called autophagy (the study of which recently garnered a Nobel Prize). (Longo is a leading fasting researcher but he’s pretty dug in — with a book about fasting, and a company that sells fasting products. He says he donates all the proceeds from the company and the book to health charities.)
That’s what happened to me. I was in ketosis for a year, lost 125lbs, but then I started eating again and poof, back came 90 of the 125 pounds 🙁 I’m finding it more difficult to get back into the swing of eating under 20 carbs a day. I find myself starving, or carb starved as it’s called, and it’s proving to be difficult, even with the meal replacement drinks. I’m going to try this fasting and see if that will help me get back to skinny, but be able to keep it off.
But followers beware, says nutrition researcher Michelle Harvie. Dieters going keto tend to lose weight, but the diets are low in fiber and high in saturated fat, which is a risk for cardiovascular disease. “And there is increasing evidence that its effect on the gut microbiome is pretty adverse,” says Harvie. “The gut microbiome is a poorly understood but potentially important part of our metabolic health. And if you mess that up, you’re in trouble.”
"How long you fast is entirely up to you and the leadership of the Holy Spirit. The Bible gives examples of fasts that lasted one day or part of a day (Judges 20:26; 1 Samuel 7:6; 2 Samuel 1:12; 3:35; Nehemiah 9:1; Jeremiah 36:6), a one-night fast (Daniel 6:18–24), three-day fasts (Esther 4:16; Acts 9:9), seven-day fasts (1 Samuel 31:13; 2 Samuel 12:16–23), a fourteen-day fast (Acts 27:33–34), a twenty-one day fast (Daniel 10:3–13), forty-day fasts (Deuteronomy 9:9; 1 Kings 19:8; Matthew 4:2), and fasts of unspecified lengths (Matthew 9:14; Luke 2:37; Acts 13:2; 14:23)." -What Christians Need to Know about Fasting by Sam Storms
Pros: According to the founders, while everyone is technically fasting every day — during the hours when we’re not eating — most of us do so haphazardly, which makes it harder to reap the rewards. Fat Loss Forever offers a seven-day schedule for fasting so that the body can get used to this structured timetable and reap the most benefit from the fasting periods. (Plus, you get a full cheat day. And who doesn’t love that?)
When we pray and fast, God promises that He will liberate us. He will loose the chains of injustice. He declares that He’ll untie the cords of the yoke and will give the oppressed their long-awaited freedom. He will set us free from the bondage of what others think, making us realize that any comparison we make with others is a guaranteed fast track to misery. When we fast and pray, God steps in and frees us from the perceived alienation with Him that has kept us immobilized, fearful, and disobedient for so long. As you consider God’s call to fasting, perhaps for the first time, you may choose to start slowly, fasting and praying for only one day. Perhaps you’ll decide to fast and pray one day each week throughout the year where you declare that specific twenty-four hours as your time of obedience to be alone in the intimate presence of God. As you do, God will give you grace, comfort, and a new direction in your Christian walk. In the end you will be set free.
Of the two most popular methods, Sasson leans toward the 5:2 schedule as slightly more manageable, since you’re only reducing your intake twice a week. But again, that’s contingent on you being a responsible dieter on your days of lowered caloric intake, which requires an immense amount of discipline—especially when it comes to remembering to drink water. “You can go a long time without food, but only a few days without adequate hydration,” she warns.
People who use insulin or drugs like metformin need to eat regularly, warns Foroutan. "If you go too long between meals you risk having your blood sugar fall way too low, which could be incredibly dangerous.” Skipping breakfast or avoiding snacks can be especially bad for people with diabetes because having consistent meals can prevent spikes in blood sugar and strengthen the effectiveness of their medication.
Not only that, but growth hormone is increased during fasted states (both during sleep and after a period of fasting). Combine this increased growth hormone secretion:, the decrease in insulin production (and thus increase in insulin sensitivity ), and you’re essentially priming your body for muscle growth and fat loss with intermittent fasting.
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.”
While this verse applies to our eternal destiny, the principle applies to our daily sojourn; as we humble and deprive our bodies through fasting, our spiritual man is made stronger and our senses more acute. This principle served the apostles well during the early church days. Their decisions were made through fasting and prayer; God gave them instructions and directions. “While they were worshiping the Lord and fasting, the Holy Spirit said, ‘Set apart for me Barnabas and Saul for the work to which I have called them.’ So after they had fasted and prayed, they placed their hands on them and sent them off” (Acts 13:2-3).
Fasting has been used in Europe as a medical treatment for years. Many spas and treatment centers, particularly those in Germany, Sweden, and Russia, use medically supervised fasting. Fasting has gained popularity in American alternative medicine over the past several decades, and many doctors feel it is beneficial. Fasting is a central therapy in detoxification, a healing method founded on the principle that the build up of toxic substances in the body is responsible for many illnesses and conditions.
Fasting is always practiced prior to surgery or other procedures that require general anesthesia because of the risk of pulmonary aspiration of gastric contents after induction of anesthesia (i.e., vomiting and inhaling the vomit, causing life-threatening aspiration pneumonia). Additionally, certain medical tests, such as cholesterol testing (lipid panel) or certain blood glucose measurements require fasting for several hours so that a baseline can be established. In the case of a lipid panel, failure to fast for a full 12 hours (including vitamins) will guarantee an elevated triglyceride measurement.