Table 1.

Main types of intermittent fasting.

Fasting Paradigms	Characteristics
Alternate Day Fasting (ADF)	Ad libitum feeding cycles for 24 h alternated with 24 h of total fasting (no caloric intake). Modified alternate day fasting (25% of caloric needs maintained; consumption of approximately 500 kcal on “fasting” days) is the predominant type of IF in the literature [30,31]
Two Days Fasting	Two consecutive or non-consecutive “fast” days, followed by five days of ad libitum food (a 2-day fast is popularly known as a 5:2 fast) [32]. Fasting days can be either full fasting or keeping to 25% of caloric needs. Also, they can be consecutive or non-consecutive [31,32].
Time-Restricted Feeding (TRF)	This type of fast limits food intake to a daily eating window of 4–10 h, promoting a fasting period of 14–18 h. This intervention reduces the opportunity to eat, tending to reduce food intake. However, it does not necessarily imply caloric restriction [33]. An early restriction of the feeding window involves shifting the feeding window to an earlier part of the day, from morning to mid- or late afternoon, aligning feeding periods with the body’s circadian rhythm [32].
Religious Fasting	Fasting is an ancestral practice, present in different religions. Although religious fasts have spiritual purposes, they can also impact physical and mental health in different ways [33]. The most extensively studied religious fast for health effects is the Ramadan fast (JR). Ramadan is one of the five pillars of Islam and occurs during the ninth month of the Islamic lunar calendar, in which healthy adult Muslims abstain from the consumption of food and fluids from dawn (el fajr) until sunset, for approximately 30 days. The duration of the daytime fast varies and is significantly impacted by location and season. In general, the typical duration of the fasting period is 10 h, but it can exceed 18 h [34].