Hoddy suggests trying a plan for two weeks and keeping a record of how you feel and what you eat. You can switch to another one if it's making you grumpy, or you can modify it; when Hoddy fasted, she split one meal into two smaller ones on fast days so she could have dinner with her husband. Or follow a plan partway, says Peterson. "Any form of fasting helps burn fat, and extending your overnight fast a little—say, eating dinner earlier—is an overall health benefit."
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.