Do Fasting Diets Work?

Medically Reviewed by Jabeen Begum, MD on September 06, 2023
3 min read

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 long after you finish fasting.

If your goal is to detox your body, you should know that 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 foods. And on some plans, you fast every other day.

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 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 feel less hungry at first. But once you stop 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 lost weight, even when they ate all they wanted on days when they weren't fasting. But the weight loss didn't last over time.

Fasting for a few days probably won't hurt most healthy people, provided they don't get dehydrated.

Your body needs vitamins, minerals, and other nutrients from foods to stay healthy. If you don't get enough, you can have symptoms such as fatigue, dizziness, constipation, dehydration, and being unable to tolerate cold temperatures.

Other people who shouldn't fast include those who are pregnant or breastfeeding, anyone with a chronic disease, older people, and children.

Research on animals has shown that intermittent fasting—in which you don't eat for a certain time during every day or week—might have health benefits beyond those that come with weight loss. Early human studies show that fasting may help with health issues related to inflammation such as arthritis, stroke, asthma, and Alzheimer's disease, but more research is needed.

Juicing is a technique used to extract raw juice from fruits and vegetables. You put pieces of fruits or vegetables into a juicing machine. The machine uses force to turn the produce into pulp and then separates the juice from the remaining fiber.

Juicing is different from blending. When you blend fruits or vegetables to make a smoothie, the fiber from the food remains inside the beverage. It's also different than store-bought juice, which can contain added sugars and may be made from concentrate.

A juice fast usually lasts 1-10 days. There are different methods of following a juice fast. On some fasts, you drink only freshly pressed juice, while on others, you eat additional food during the fast.

Juice fasting benefits

Juicing and juice fasting may offer a few benefits. Most of these changes happen on a microscopic level inside your body.‌

  • May help gut health. A proper balance of bacteria inside the gut is essential for good health. One small study found that a juice fast could leave you with more of a type of "good" bacteria in your gut that promotes weight loss. ‌But other research found juice fasting had little effect on gut bacteria.

  • Helpful for people who struggle with eating fruits and vegetables. Juicing can be a good solution if you don't enjoy eating fruits and vegetables but still want to take advantage of their benefits.

Juice fasting risks

  • Short-term weight loss. You're likely to drop a few pounds during the fast,but expect them to come back once you resume your normal diet.‌

  • Possible protein deficiency. The CDC recommends 56 grams of protein each day for men and 46 grams per day for women. Although fruits and vegetables contain small amounts of protein, it's hard to get enough from juice alone.

  • Feeling hungry and tired. Although it can be delicious, freshly pressed juice doesn't leave you feeling full. You could have sugar spikes just after drinking juice that leave you feeling weak and sluggish.

‌Always check with your doctor before starting any new diet or cleanse. You can also ask your doctor for a referral to a registered dietitian, who can show you how to design a healthy eating plan.