Table 1.

Types of intermittent fasting regimens that are hypothesized to impact health outcomes

Complete Alternate Day Fasting	These regimens involve alternating fasting days (no energy-containing foods or beverages consumed) with eating days (foods and beverages consumed ad-libitum).
Modified Fasting Regimens	Modified regimens allow for the consumption of 20–25% of energy needs on scheduled fasting days. This regimen is the basis for the popular 5:2 diet, which involves severe energy restriction for 2 non-consecutive days a week and ad libitum eating the other 5 days.
Time-Restricted Feeding	These protocols allow individuals to consume ad libitum energy intake within specific windows, which induces fasting periods on a routine basis. Studies of <3 meals per day are indirect examinations of a prolonged daily or nightly fasting periods.
Religious Fasting	A wide variety of fasting regimens are undertaken for religious or spiritual purposes.
Ramadan Fasting	A fast from dawn to sunset during the holy months of Ramadan. The most common dietary practice is to consume one large meal after sunset and one lighter meal before dawn. Therefore the feast and fast periods of Ramadan are approximately 12 hours in length.
Other Religious Fasts	Latter Day Saints followers routinely abstain from food and drink for extended periods of time. Some Seventh-day Adventists consume their last of 2 daily meals in the afternoon, resulting in an extended nighttime fasting interval that may be biologically important.