Maintaining certain time frames for eating can make fasting easier. One type of fasting is known as a 12-hour fast. Here’s how it works: Once you stop eating at night, you wait 12 hours until you eat again. For example, if you finish dinner at 9 p.m., you should not start eating breakfast until 9 a.m. This fasting method is great for people who want to try fasting but have fluctuating schedules and need the flexibility.

A diagnostic fast refers to prolonged fasting from 8–72 hours (depending on age) conducted under observation to facilitate the investigation of a health complication, usually hypoglycemia. Many people may also fast as part of a medical procedure or a check-up, such as preceding a colonoscopy or surgery. Fasting may also be part of a religious ritual.