Intermittent fasting (IF) is a generalized term used to describe cycles that alternate between periods of restricting calories and periods of not restricting calories. During the restriction period, individuals may either limit, or completely avoid calorie containing foods and beverages. There are a number of variations of fasting, but some of the more common approaches are defined here.
Time Restricted Feeding (TRF) describes a shortened window of time when a person consumes calories from food and beverages. This is also called “prolonged nightly fasting” and usually extends a person’s typical overnight fast. For example, a person may only consume calories between the hours of 8am – 4pm. Typically, a stretch of 12-16 hours without eating fulfills the criteria for time-restricted feeding.
Alternate Day Fasting (ADF) also called fasting intervals, describes a cycle of fasting on one day and eating on the next day. On fasting days, people typically restrict calories to no more than 600 per day. Some individuals may only consume water and electrolytes on these fasting days. Alternate day fasting can also refer to fasting every third day, or fasting on a more personalized schedule.
Modified Fasting describes a type of fast in which a person restricts calories by 20-30%, or reduces calories to 600 per day for a specified number of days per week. This type of fast is also called intermittent energy restriction.
Fasting Mimicking Diet (FMD) describes a ketogenic diet that is typically followed for five days once a month. This 5-day, very low-calorie, low carbohydrate, structured food plan has been shown in a limited number of studies to improve body composition and lower blood pressure after three consecutive cycles (3 months).2
