It's possible to lose weight while fasting -- if you don't eat anything for a day or two, you'll probably weigh in several pounds lighter on the scale, according to Cornell University. However, you won't lose that weight in fat. Instead, you'll lose water and muscle tissue while fasting, and you'll probably regain that weight almost immediately once you start to eat again.
Fasting Facts
Most people burn around 2,000 calories per day or more, so when you fast -- and fail to eat any calories to maintain your weight -- you should in theory lose some fat, according to Columbia University. One pound of fat equals 3,500 calories, meaning you need to burn 3,500 calories more than you eat to lose that pound. However, once you start to fast your body slows down its metabolism in response to what it sees as a threat of starvation, sabotaging your weight loss.
Liquid Fasts
If you want to lose weight, you potentially can counter this "starvation mode" response by your body by taking in some calories, potentially in the form of liquid protein shakes. Physician-supervised weight loss programs use this form of modified fasting to induce fast weight loss in obese patients that need to lose significant weight, according to Thomas Jefferson University. Commercial liquid diet shake programs offer another option, although you should check with your physician before following one.
Research
If you fast for a day or two, you probably won't overeat to compensate once you begin eating normally again, according to Cornell University. In fact, if you fast for one day every week -- as opposed for fasting for longer periods less often -- you might actually lose some weight over time. It takes up to two weeks for the body to recover the muscle and water weight lost during a one-day fast, so once-weekly fasts could lead to ongoing, sustained weight loss.
Considerations
Fasting potentially can cause health problems, most of which represent inconveniences but some of which could be serious, according to Columbia University. For example, you may experience constipation, dizziness or even nausea while fasting. In addition, some people who fast for longer periods experience gallstones and heart rhythm malfunctions, according to Vanderbilt University. Check with your doctor before starting any diet, especially a fasting program.
References
- Columbia University: How Many Calories Does It Take To Lose One Pound?; Nov. 17, 2007
- Columbia University: Can Fasting Help Purge the Body of Toxins?; Nov. 11, 2008
- Cornell Chronicle: Fasting and Diets; Ted Boscia; March 26, 2010
- Thomas Jefferson University: Weight Management: What To Expect
- Vanderbilt University: Liquid Diets Complete
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