Chris Pratt! Hugh Jackman! Halle Berry! Kourtney Kardashian! What these celebrities have in common, other than a gratuitous exclamation point after their names, is a professed fondness for intermittent fasting, the diet craze turning the fitness world on its sweaty, well-toned head. For help determining whether you, too, should incorporate this into your 2019 resolution-related plans, we asked a few experts to explain what it is, why people love it, and whether it’s really worth the pain of forgoing on-demand snacks for the rest of the winter.
For example, in the graphic below you would eat dinner on Monday night and then not eat again until Tuesday evening. On Wednesday, however, you would eat all day and then start the 24–hour fasting cycle again after dinner on Wednesday evening. This allows you to get long fast periods on a consistent basis while also eating at least one meal every day of the week.
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.
Intermittent fasting is easy to follow in that it does not limit or restrict food, allows one to eat without tightly tracking calories, and will not place a burden on your social life (i.e. not being able to go out to dinner and order something on the menu). It also can make life much easier as there is less time spent cooking, eating, and cleaning up.
What and when you eat during the feeding window also depends on when you work out. On days you exercise, carbs are more important than fat. On rest days, fat intake should be higher. Protein consumption should be fairly high every day, though it will vary based on goals, gender, age, body fat and activity levels. Regardless of your specific program, whole, unprocessed foods should make up the majority of your calorie intake. However, when there isn’t time for a meal, a protein shake or meal replacement bar is acceptable (in moderation).
The increase in longevity is also clearly associated with a decrease in disease states that would cut your life short, and calorie restriction is associated with a number of health improvements, including reduced visceral fat, reduced inflammation, lower blood pressure, and improved insulin sensitivity,5,6 just to name a few. Earlier research has demonstrated that calorie restriction helps extend the lifespan of animals by improving insulin sensitivity and inhibiting the mTOR pathway.
If you really want to lose fat, intermittent fasting is the perfect tool. Research shows that intermittent fasting — cycling in and out periods of fasting and eating — has huge benefits for your body and brain. It can ward off chronic disease, improve memory and brain function, and boost your energy levels. What’s more, intermittent fasting is a powerful hack for losing weight quickly, and keeping it off.
Prolonged very low calorie diets can cause physiological changes that may cause the body to adapt to the calorie restriction and therefore prevent further weight loss.  Intermittent fasting attempts to address this problem by cycling between a low calorie level for a brief time followed by normal eating, which may prevent these adaptations. However, research does not consistently show that intermittent fasting is superior to continuous low calorie diets for weight loss efficiency.
In her blog, Gospel Taboo, Amanda Edmondson writes, "Biblically, fasting is mentioned in both the Old and New Testament. In the Old Testament it was often a way of expressing grief or a means of humbling one's self before the Lord. In Psalm 35:13, David humbled himself with fasting. In the New Testament it was a means to grow closer to God through mediating and focusing on Him. In Matthew 4:1-2, Jesus went to the wilderness to fast for 40 days. In Matthew 6:16-18 we learn that we aren’t to look somber while fasting so that it’s not obvious to others when we are fasting. Throughout the New Testament fasting and prayer are often mentioned together. In Acts 13:3, ‘they had fasted and prayed.’ In Luke 2:37 a widow worshiped day and night fasting and praying."
In 2012, Carolyn Corbin, who lives in the Channel Islands, got some firsthand experience with fasting’s flexibility. At 5 feet, 2 inches tall and 159 pounds, Corbin was overweight, with a BMI of 29.1. After seeing Mosley’s BBC show, she took up the 5:2 regimen, eating 500 calories two days a week and eating normally the rest of the time. She soon switched to water-only fasts two days a week. Since taking up the practice, the 65-year-old has lost 35 pounds and kept it off. “Forget calorie counting, diet food and diet drinks,” Corbin says. “Fasting for weight loss works.”
Fasting is to be done with the object of seeking to know God in a deeper experience (Isaiah 58:1; Zechariah 7:5). Fasting relates to a time of confession (Psalms 69:10). Fasting can be a time of seeking a deeper prayer experience and drawing near to God in prevailing prayer (Ezra 8:23; Joel 2:12). The early church often fasted in seeking God's will for leadership in the local church (Acts 13:2). When the early church wanted to know the mind of God, there was a time of prayer and fasting.
Promote human growth hormone production (HGH). Fasting can raise HGH by as much as 1,300 percent in women and 2,000 percent in men.12 HGH plays an important part in health, fitness, and slowing the aging process. It's also a fat-burning hormone Lower triglyceride levels and improve other biomarkers of disease Boost production of brain-derived neurotrophic factor (BDNF), stimulating the release of new brain cells and triggering brain chemicals that protect against changes associated with Alzheimer's and Parkinson's disease. (Alternate-day fasting — restricting your meals on fasting days to about 600 calories — can boost BDNF by 50 to 400 percent, depending on the region of the brain.13
When Varady and her colleagues conducted a study that combined alternate day fasting and exercise, they allowed the participants to pick whether they wanted to exercise on a feasting or fasting day, and found there was no strong preference one way or the other. But the researchers were surprised the dieters actually reported feeling more energetic on fasting days.
Hunger suppression. A ketogenic diet suppresses hunger, too. On a keto diet, your liver turns fat into little bundles of energy called ketones, which it then sends through your bloodstream for your cells to use as fuel. Ketones suppress ghrelin, your body’s main hunger hormone. High ghrelin makes you hungry. On keto, your ghrelin stays low, even when you don’t have food in your system. In other words, you can go longer without eating and you won’t get hungry. Fasting becomes significantly easier on keto so you can fast for longer windows to reap all the benefits.
The bigu (辟谷 "avoiding grains") fasting practice originated as a Daoist technique for becoming a xian (仙 "transcendent; immortal"), and later became a Traditional Chinese medicine cure for the sanshi (三尸 "Three Corpses; the malevolent, life-shortening spirits that supposedly reside in the human body"). Chinese interpretations of avoiding gu "grains; cereals" have varied historically; meanings range from not eating particular foodstuffs such as food grain, Five Cereals (China), or staple food to not eating anything such as inedia, breatharianism, or aerophagia.
“I used to crave foods like crazy when I first started,” says Dr. Sylvia Tara, author of The Secret Life of Fat, in a Bulletproof Podcast episode. “after six to eight weeks, I didn’t feel it anymore.” Dr. Tara kept a journal or foods and schedules to find how fasting worked for her. Her advice for weight loss with intermittent fasting? “For people who have those 20 pounds, know, number one, it can be done. Number two, it might be a bit more effort than you thought it was going to be… Third, know that it gets easier with time and you can maintain it. It really isn’t as bad once you get into it, and it’s extraordinarily effective.”
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.
No, it's not a cure-all for creaky joints, wrinkled skin, or brittle hair, but IF prompts an increase in human growth hormone (HGH), which promotes cellular repair, says Foroutan. She explains that not eating for several consecutive hours creates a slight stress on your cells' mitochondria (the energy powerhouses), which gives them a nudge to rev up their functioning. IF might also be helpful for brain health; animal studies suggest that this eating pattern might serve to ward off age-related cognitive decline.
Alternative medicine A period of voluntary abstinence from foods and/or drinks; fasting is integral to many religions, as it is believed to purify the mind and spirit; fasting rests the GI tract, and may rid the body of toxins and undigested metabolites; fasting leads to a loss of water, Na+, and K+, resulting in postural hypotension, and decreased blood sugar resulting in depression, fatigue, decreased libido, and malaise, increased nitrogen in the circulation due to protein breakdown, and may result in premature childbirth—Yom Kippur effect
While the idea of fasting can be overwhelming, especially if you haven’t done it before, intermittent fasting can actually be a lot easier than many other types of eating plans. Since you are fasting for time restricted chunks of the day, you’ll be eating less food, which eliminates a lot of the stress around having to meal prep. During the periods of time in which you're eating, you’ll still want to focus mainly on healthy fats, clean protein, and carbohydrates from whole food sources—but this isn’t an excuse to hit the drive-thru and load up on sugar the rest of the time! Here are some of the effects of intermittent fasting:
For Eastern Orthodox Christians, fasting is an important spiritual discipline, found in both the Old Testament and the New, and is tied to the principle in Orthodox theology of the synergy between the body (Greek: soma) and the soul (pneuma). That is to say, Orthodox Christians do not see a dichotomy between the body and the soul but rather consider them as a united whole, and they believe that what happens to one affects the other (this is known as the psychosomatic union between the body and the soul). Saint Gregory Palamas argued that man's body is not an enemy but a partner and collaborator with the soul. Christ, by taking a human body at the Incarnation, has made the flesh an inexhaustible source of sanctification. This same concept is also found in the much earlier homilies of Saint Macarius the Great.