Table 1.

Human fasting regimens (by intensity, frequency, and duration).

Intensity of Food and Drink Restriction	Frequency and Duration of Fasting Periods	Common Combinations Used in Human Studies
“Pure” fasting (no food or drink, often in the context of religious practices)	Time-restricted feeding (daily four-to-twelve hour eating window)	Water/fluid-only time-restricted feeding
Water-only fasting (only water is permitted, plus salt and micronutrients)	Alternate-daily fasting (fasting every other day)	Water/fluid-only alternate-daily fasting
Fluid-only fasting (water-only fast plus calorie-free fluids, such as tea and black coffee)	Two-days-per-week fasting (fasting two consecutive days per week)	Limited calorie intake two-days-per-week fasting
Limited calorie intake fasting (up to 250–500 kcal per day, via vegetable or bone broths)	Periodic fasting (fasting periods two days to three weeks in duration)	Limited calorie intake periodic fasting