Also, for many people, a full 16 hours of fasting just isn’t realistic, says Cynthia Sass, a New York City– and L.A.-based performance nutritionist. She recommends 12 hours of overnight fasting at most and believes the 16-hour gap is especially tough on those who exercise early in the morning or late at night. “If fasting makes you feel miserable and results in intense cravings and rebound overeating, it's not the right path for you,” she says.
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.
In the process of revising the Book of Common Prayer in various provinces of the Anglican Communion the specification of abstinence or fast for certain days has been retained. Generally Lent and Fridays are set aside, though Fridays during Christmastide and Eastertide are sometimes avoided. Often the Ember Days or Rogation Days are also specified, and the eves (vigils) of certain feasts.
Maintaining certain time frames for eating can make fasting easier. One type of fasting is known as a 12-hour fast. Here’s how it works: Once you stop eating at night, you wait 12 hours until you eat again. For example, if you finish dinner at 9 p.m., you should not start eating breakfast until 9 a.m. This fasting method is great for people who want to try fasting but have fluctuating schedules and need the flexibility.
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
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.
The participants ended up eating 350 fewer calories a day compared to a control group just because they couldn’t squeeze in their normal food intake between 10 a.m. to 6 p.m., the prescribed eating window in the study, said Krista Varady, co-author and an associate professor of nutrition at the University of Illinois, Chicago, who has been studying fasting for 12 years.
In a paper published in 2002 on the pseudo-experiment, Walford and colleagues reported that the Biosphere staff had been in excellent health. Nearly all of them lowered their blood pressure, blood sugar, cholesterol and other health measures. Still, their skeletal appearance was shocking. “They were malnourished, and they didn’t look healthy,” says Eric Ravussin, a metabolic researcher at the Pennington Biomedical Research Center in Baton Rouge, Louisiana.
Longer fasts likewise can take the form of abstinence from food or some other sacrifice. Some good options for a non-food fast would be abstaining from watching TV from Monday to Friday, reading a biography of a great man or woman of God each week, or dedicating every evening for a week to praying with friends...A longer water-only fast might last from one to three days. If you are fasting from something other than food, your longer fast might last a week. Some use Lent as a time for a longer fast.
César Chávez undertook a number of spiritual fasts, including a 25-day fast in 1968 promoting the principle of nonviolence, and a fast of 'thanksgiving and hope' to prepare for pre-arranged civil disobedience by farm workers. Chávez regarded a spiritual fast as "a personal spiritual transformation". Other progressive campaigns have adopted the tactic.