Overview

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.

Fasting to lose weight.

Some people use fasting as a way to lose weight. There are different kinds of fasting for weight loss. They all require limiting food (or not eating at all) on certain days of the week or during certain times of the day. Experts don't agree on whether fasting is a healthy way to lose weight and keep it off over time.

Intermittent fasting.

This is a type of fasting that limits food on certain days or during certain times of the day. For example, one form involves eating only between the hours of 8 p.m. and noon the following day. People sometimes use intermittent fasting to try to lose weight. You may hear other terms used to describe it, such as alternate-day fasting or 5-to-2 (5:2) fasting.

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.