Dietrich Bonhoeffer, in his book The Cost of Discipleship, said, “Jesus takes it for granted that His disciples will observe the pious custom of fasting. Strict exercise of self-control is an essential feature of the Christian life. Such customs have only one purpose — to make the disciples more ready and cheerful to accomplish those things which God would have done.”
An understanding of the physiological effects of fasting began to evolve in the latter part of the 19th century, when some of the first organized studies of fasting were carried out in animals and humans. In the 20th century, as more became known about nutrition and the nutritional requirements of the human body, methods of fasting became increasingly sophisticated, and a wide array of approaches emerged. For example, fasting was used as a treatment and as a form of disease prevention, and it was carried out in various settings (e.g., in a hospital or clinic or at home). Some fasting methods, particularly those applied in the treatment of chronic diseases, lasted more than a month, allowed for the consumption of only water or calorie-free tea, and included exercise and enemas. Other methods, generally referred to as modified fasting, allowed for the intake of 200 to 500 kilocalories per day (daily calorie needs of adults range from about 1,600 to 3,000 kilocalories, depending on sex, age, and activity level) and sometimes included psychological or spiritual therapy; depending on the particular method used, calories usually were in the form of bread, vegetable broth, fruit juice, honey, or milk. Modified fasting was distinguished from a very low-calorie diet, which allowed up to 800 kilocalories per day and typically was aimed at inducing substantial weight loss. Intermittent fasting involved cyclic periods of calorie restriction, such as a 24-hour period of fasting followed by a 24-hour period of regular calorie consumption.
Well, most notably, it’s a great way to get lean without going on a crazy diet or cutting your calories down to nothing. In fact, most of the time you'll try to keep your calories the same when you start intermittent fasting. (Most people eat bigger meals during a shorter time frame.) Additionally, intermittent fasting is a good way to keep muscle mass on while getting lean.
There are many promises God makes in His Word in regard to the blessings we will receive through prayer and fasting. In my book The Power of Prayer and Fasting, I talk about seven specific promises. I want to mention three of them here that I trust will bless you as you read. I have seen each of these promises come true in my walk with God, and I’m confident they also can live in you, through you, and will be yours as you call on God to do His will in your life.
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.

Study after study confirms that any form of intermittent fasting will help reduce weight and improve body composition, though the results are probably about the same as you’d see from restricting your calories. One study Varady ran, published in 2017 in JAMA Internal Medicine, found that after dieting for one year, people lost about 5–6% of their bodyweight whether they restricted their calories or tried alternate-day fasting.
When you consistently eat every few hours and never miss a meal, your body becomes very inefficient at burning fat as a fuel, and this is where the trouble starts. It's important to recognize that, with few exceptions, you cannot burn body fat if you have other fuel available, and if you're supplying your body with carbohydrates every few hours, your body has no need to dive into your fat stores. When you apply intermittent fasting you not only avoid this but also will typically decrease your food costs and increase your health.

Whether you are considering a 12-hour fast, a two-day fast, or a daily low calorie fast, you should talk to your doctor before beginning a new eating regimen. Certain medical conditions may get worse with sudden changes in diet and some medications are affected by changing the foods you eat. A doctor can help you weigh the possible benefits and consequences of a fast to see if it’s right for you.
A diagnostic fast refers to prolonged fasting from 8–72 hours (depending on age) conducted under observation to facilitate the investigation of a health complication, usually hypoglycemia. Many people may also fast as part of a medical procedure or a check-up, such as preceding a colonoscopy or surgery. Fasting may also be part of a religious ritual.