You don't have to eat when you are closed to the outside world, but this is generally aimed at old practitioners and it is not recommended to do initial training. Generally, people who are closed to the outside world don't eat after noon, but strictly speaking, both Japan and China eat a meal and don't eat after noon. Adopting the above methods can reduce desire and improve practice. People who practice for one day and one night can skip meals for seven days and seven nights at most. For security reasons, it is generally not recommended.