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Do Fasting Diets Work?

Some people fast as a way to lose weight. Others fast to try to detox their bodies, or for religious reasons.

If you're fasting to lose weight, you may want to reconsider. The weight loss may not last after you finish fasting.

If your goal is to detox your body, you should know that there's no proof that it works. Your body naturally detoxes itself.

Fasting diets aren't all the same. Some allow only liquids like water, juice, or tea. Others cut calories drastically, but don't completely ban food. And on some plans, you fast every other day.

Why Fasting for Weight Loss Can Backfire

When you eat less than you need and you lose weight, your body goes into a starvation mode. To save energy, your metabolism slows down.

When you're done fasting and you go back to your usual diet, you may regain the weight you lost, and then some.

On a fast, your body adjusts by curbing your appetite, so you will feel less hungry at first. But once you have stopped fasting, your appetite revs back up. You may feel hungrier and be more likely to overeat.

Fasting every other day has similar results. It helps people lose weight, but not for long.

In one study, people who fasted every other day shed weight, even when they ate all they wanted on days when they weren't fasting. But the weight loss didn't last over time.

Is Fasting Safe?

Fasting for a few days probably won't hurt most people who are healthy, provided they don't get dehydrated. But fasting for long periods of time is bad for you.

Your body needs vitamins, minerals, and other nutrients from food to stay healthy. If you don't get enough, you can have symptoms such as fatigue, dizziness, constipation, dehydration, and not being able to tolerate cold temperatures. Fasting too long can be life-threatening.

Don't fast, even for a short time, if you have diabetes, because it can lead to dangerous dips and spikes in blood sugar.

Other people who should not fast include women who are pregnant or breastfeeding, anyone with a chronic disease, the elderly, and children.

Before you go on a new diet, particularly one that involves fasting, ask your doctor if it's a good choice for you. You can also ask your doctor for a referral to a registered dietitian, who can show you how to design a healthy eating plan.

WebMD Medical Reference

Reviewed by Brunilda Nazario, MD on March 20, 2014
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