While there is no single definition for IF (also referred to as intermittent energy restriction, or IER), it essentially means restricting caloric intake for a certain period of time. There are three common ways fasting is implemented:

• Time-restricted feeding: Fasting 12 to 21 hours per day and having a specified eating window to consume food without restricting calories
• Alternate-day fasting: Going a full day without eating
• Modified fasting: Periods of severely limited food intake (5:2= 5 days normal eating, 2 days restricted intake)

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