Simply put, intermittent fasting (IF) is a type of eating pattern in which you eat and fast within specific time windows. There are a variety of ways to do IF, with 12:12 (you eat within a 12-hour window and fast for 12 hours) and 16:8 (eating in an eight-hour window and fasting the other 16) being two of the most popular methods. Unlike other ways of eating, you don't have to restrict what you consume when following IF.