From a Christian perspective, there are many options. One may go on only fruits and vegetables for a day or more. One may do a complete fast, involving only water and no food for a specific period of time. One may skip breakfast intentionally to pray and focus on God, and then eat lunch. Caloric restriction, especially when one is not doing complete food fast, offers the opportunity to live what some have described as a “fasted life.” The key is to choose a plan that works for you at that time and to start small. In all cases, the important thing is to intentionally focus on God in prayer.

So if both musicians and adamantium-clawed superheroes do Intermittent Fasting, it can probably work for you too, if you can make it work for your particular lifestyle and situation! If you’ve tried implementing something like this in the past and not had success, or you’re just looking for guidance from a coach to help you implement it into your lifestyle, I hear ya!
This depends. If you’re on a time-restricted fast and you’re in no-eating hours, it’s best to stick to no- or low-calorie drinks like water, coffee (with no milk) and tea. If you’re on an alternate day diet or something similar, even during low calorie hours, you can technically drink whatever you’d like — but remember, this will count against your calories. Would you rather spend 100 calories on an apple or a glass of milk? It’s your call.
An informative description of the proclamation of a fast is in Jeremiah 36:9. There the people of Judah convened, apparently for the purpose of national repentance. This at least is what Jeremiah instructed Baruch to encourage them to do (vv. 7-8). Moreover, Jeremiah refers to the anticipated event as a "day of fasting" (v. 6), suggesting a common practice known to him and the people generally. In fact, Isaiah had spoken of such convocations a century earlier ( 58:3-6 ), gatherings on special days for special purposes. Regardless of Isaiah's feelings about the abuse of fasting, it is obvious that he recognized it as a legitimate form of worship and that he found no fault with it being carried out on specially called occasions.
Where diets complicate life, fasting simplifies. Where diets are expensive, intermittent fasting is free. Where diets can take time, fasting saves time. Where diets are limited, fasting is available anywhere. Where diets have variable efficacy, fasting has unquestioned efficacy. There is no more powerful method for lowering insulin and decreasing body weight.
Often fasting is done for medical or health reasons, or in an attempt to lose weight. For many other people, fasting is an important part of their religious observance. Fasting is done by Muslims, Christians, Buddhists, and Jews, among other groups. Fasting comes from fast, which in turn has an Old English root, fæsten, "voluntary abstinence from food or drink, especially as a religious duty."
Mattson points out that, from an evolutionary perspective, the brain power that fasting generates makes sense. Mammals typically go days without food, often hunting on an empty belly. Semi-starved animals with enhanced smarts and energy would be more likely to obtain food and live another day. “If you are that wolf or lion, now a week with no food, you better be able to focus your mind and concentrate on what you need to do to get food,” he says.
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.
Expect funny looks if you spend a lot of mornings with breakfast eaters.  A few weeks back I had a number of friends staying with me, and they were all completely dumbfounded when I told them I didn’t eat breakfast anymore. I tried to explain it to them but received a bunch of blank stares. Breakfast has become so enGRAINed (zing!) in our culture that NOT eating it sounds crazy.  You will get weird looks from those around you…embrace it. I still go to brunch or sit with friends, I just drink black coffee and enjoy conversation.
Another aspect of fasting for God is comparable to a person dedicating an action to a cause. For God and country was, at one time, a familiar declaration in the United States.  It implied that the action being taken was to answer a noble call and serve a higher motive, the expectation of reward or compensation being far removed. The motivation came from a spiritual, emotional and dedicated commitment to do what is right. Similarly, a fast may be undertaken for God because it represents a lofty act, a selfless commitment to an act considered meritorious and virtuous.
Of course, fasting — regardless of the method — isn’t for everyone. If you have any medical conditions or special dietary requirements, it’s smart to consult a doctor before giving intermittent fasting a shot. Anyone who tries it should also plan to be highly self-aware while fasting. If it’s not agreeing with you, or if you need to eat a little something to hold you over, that’s just fine. It takes our bodies time to adjust, and some require more than others. Keep in mind that hormones can make it harder for women to follow a fasting plan than for men. “Be cautious at first, and start slowly [with a shorter fast],” Shanks recommends. If it doesn’t make you feel better, try something different, or accept the fact that maybe fasting isn’t for you.
Although it’s possible that fasting helps manage blood sugar and insulin, fight inflammation, and ease sleep problems, most people follow a fasting diet to lose weight. Fasting is believed to help in this goal because of the effects that caloric restriction and extended periods without food have on metabolism, or simply because people eat less during the restricted feeding window. (Some dieters benefit from the structure and clear boundaries fasting plans offer.)
Research7,8,9 has shown that intermittent fasting results in many of the same benefits as calorie restriction — even if you don't place any restrictions on the number of calories you consume when you do eat. This was demonstrated in a 2013 review,10 which found a broad range of therapeutic benefits of intermittent fasting, even when total calorie intake per day did not change, or was only slightly reduced. Research included in that review, and other published studies, indicate that intermittent fasting can help:
Even though this plan is advanced, it's very simple. Don't eat anything every other day. This is the most intense form of fasting but can produce amazing results. Every other day, eat healthy fats, clean meat sources, vegetables, and some fruit, and then on your fasting days, you can consume water, herbal tea, and moderate amounts of black coffee or tea.
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?)
Weight-loss resistance can often be due to an underlying hormone imbalance. Leptin resistance occurs when your brain stops recognizing leptin's signals to use your body’s fat stores for energy. This causes your body to continually store fat instead of using it. Intermittent fasting has been shown to improve chronic inflammation that can dull the brain’s leptin receptor sites.
Physician Roy Walford was one of the scientists. He also happened to be a CR devotee and had recently written a book on living to the age of 120 by following the regimen. Soon after entering, the team realized the food they raised in the dome wouldn’t be enough to sustain them. So Walford implemented an impromptu CR experiment. The four men and four women reduced their approximate calorie intake by up to 30 percent. It was essentially the first human study of CR and its effects.
The second one is more subtle: The body shifts into fat-burning mode when it doesn’t get food for an extended period of time. That’s because the body’s first source of fuel is glycogen, and it only turns to burning body fat once that quickly available energy source is depleted. So when you fast for long enough, you drive down stores of glycogen and start burning fat tissue. “In people, we see a change in fasting glucose — it’s lower — and abdominal fat is affected without much of an effect on the muscles,” Longo explained.

Used for thousands of years, fasting is one of the oldest therapies in medicine. Many of the great doctors of ancient times and many of the oldest healing systems have recommended it as an integral method of healing and prevention. Hippocrates, the father of Western medicine, believed fasting enabled the body to heal itself. Paracelsus, another great healer in the Western tradition, wrote 500 years ago that "fasting is the greatest remedy, the physician within." Ayurvedic medicine, the world's oldest healing system, has long advocated fasting as a major treatment.
Insulin rises when we eat, helping to store the excess energy in two separate ways. Sugars can be linked into long chains, called glycogen and then stored in the liver. There is, however, limited storage space; and once that is reached, the liver starts to turn the excess glucose into fat. This process is called De-Novo Lipogenesis (meaning literally Making Fat from New).

A healthy diet is always the key to a healthy lifestyle. It’s especially important to eat healthy if you are fasting; even though you’re eating less, you still need to take in the essential vitamins, minerals, and nutrients your body needs to function . Try to get the recommended servings of fruits and vegetables, as well as protein and grains, into your daily diet.

Cons: Even though there is flexibility in when you eat, Leangains has pretty specific guidelines for what to eat, especially in relation to when you’re working out. The strict nutrition plan and scheduling meals perfectly around workouts can make the program a bit tougher to adhere to. (You can learn more about the specifics — as well as when to time these meals — directly from Leangains here and here.)
I’m 65 and I retired recently. I tried this for one week, and I must admit I particularly watched the clock all day long. I was very intergetic, and my depression subsided most of the time. At one week I weight myself, and thought why am I doing this if I’m not losing weight? So I went off and now I feel like I drag most of the day. I’m getting back on…enough said.
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).