What is fasting?

Fasting means choosing to go without food, drink, or both for a period of time. It can mean going without any food or going without certain types of food. People may fast before a medical test or surgery, for religious reasons, or to try to lose weight.

What are the types of fasting?

Types of fasting include:

• Medical fasting. You may be asked to fast for a certain amount of time before a medical test or surgery, often 8 hours or more.
• Religious fasting. Many people fast as part of their religion. For example, people may eat nothing on certain days, eat nothing from sunrise to sunset for a certain month, or not eat foods like meat, dairy, and eggs for several weeks at a time.
• Fasting to detoxify the body. Some people fast because they believe it rids the body of toxins. But there is no evidence that toxic substances build up in a person whose liver and kidneys are normal.
• Intermittent fasting. This is a type of fasting that is often used for weight loss. There are different ways you can do this. One way is to limit the time you eat to a certain number of hours each day. For example, you might eat only between noon and 8 p.m. After 8 p.m., you wouldn't eat until noon the next day. Another way is to limit the number of calories you eat on certain days, like Tuesdays and Thursdays. Then you eat your usual amount on the other days of the week.

Is fasting safe?

For people who are healthy, some fasting is probably safe. But for people with some health conditions or who are pregnant or nursing, it might be harmful. It's a good idea to talk to your doctor before you start any new diet or weight-loss plan.