What does “16-8” or “5-2” mean? Posted on Friday October 13th, 2017Friday May 3rd, 2019 by Patrick These are the names of two well-known intermittent fasting methods. 16-8 means to fast for 16 hours and to eat for 8 hours. You can just skip breakfast, for example. 5-2 means to eat for 5 days and to fast for two whole days.