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9 Things That Happen to Your Body During a Juice Cleanse

A weight loss expert reveals how a juice cleanse can harm your body—here's what you need to know about this potentially dangerous fad.

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What is a juice cleanse?

Pretty much exactly what it sounds like—you live on mostly juice for a certain period of time. Some people do a juice cleanse to drop weight, while others use it as to "detox their body," with the belief that the approach can flush chemicals and noxious substances from the body. Every cleanse is different: Some people use a juicer to make their own drinks; others subscribe to a program that delivers the juices. Unfortunately, there's a lot of misinformation about what a juice cleanse can do for your body—and not everyone realizes how dangerous they can be. Anthony Auriemma, MD, medical director of AMITA Health's Alexian Brothers Weight Loss Solutions near Chicago, IL, explains to Reader's Digest just what happens when you choose this extreme approach. (You've heard of juicing, but here's what happens during a souping cleanse.)

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Your blood sugar will fluctuate

Fruit is a natural source of sugar, and too much sugar—even fructose—can be unhealthy. If all you're doing is guzzling fruit and vegetable juices for days, your blood glucose levels will skyrocket. "One concerning aspect of a cleanse is the large amounts of sugar found in juices, which causes a rapid rise in blood sugar," explains Dr. Auriemma. "This can cause a large release of insulin from the pancreas to counteract the blood sugar, which can be extremely dangerous for people with diabetes." Even if you don't have diabetes, the sugar rush can trigger dizziness, headaches, shaking, difficulty concentrating, and boost your hunger. Here are some other sneaky things that raise blood sugar.

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Your gut is deprived

An irony of juicing is that although you're getting more produce—in liquid form—you're missing out on one of produce's major benefits: Fiber. "Juicing robs you of the fiber in fruits and veggies. Fiber is an important part of digestion—it slows the rise in blood sugar, helps feed gut bacteria, and improves bowel function," he explains.

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Your heart suffers

You may know the dangers of high blood pressure, but did you know that low blood pressure can harm you as well? "Cleanses can cause a significant drop in blood pressure because of the loss of water. This is bad for the heart," Dr. Auriemma says. This sharp drop is particularly dangerous for anyone taking medication to treat high blood pressure. Symptoms of low blood pressure include lightheadedness, jitteriness, lack of concentration, and mood changes.

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Your metabolism slows

Most people trying to lose weight know that their metabolism is key to burning calories. A juice cleanse can sabotage your metabolism, though. Your tummy may look and feel trimmer while you're on a cleanse, but that constant flow of juice is missing the necessary protein and healthy fats your body needs. "Juicing slows the metabolism because your body doesn't understand why it's not getting enough calories, so it slows down the breakdown of food into energy," Dr. Auriemma says. If you're self-conscious about your waistline, make sure you avoid these bad habits for belly fat.

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Your muscles will shrink

"Due to the lack of protein in cleanses, your body will start to lose lean muscle mass," says Dr. Auriemma. If dropping pounds is your goal—especially over the long term—look out: "Losing muscle works against you because muscle burns more calories than fat."

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Your body is depleted of water

Weirdly, liquid-based diets can actually strip your body of liquid, partially due to increased urination. "This can lead to a dangerous condition called hyponatremia, which means there's not enough sodium in the blood; in its most severe form, this can lead to seizures," Dr. Auriemma cautions. Here are some other sneaky ways you can become dehydrated.

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You'll be tired all the time

Lack of calories, dehydration, and lost muscle mass will zap your body of energy, says Dr. Auriemma. Once the sugar rush from the juice wears off, you'll crash and feel sluggish. Eat to beat fatigue with these energy-boosting foods.

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You'll lose weight, but only temporarily

Although your scale may indicate your shedding pounds, "it's likely due to the loss of water or muscle," says Dr. Auriemma. Once you start eating solid food again, any lost weight will come right back—though the valuable, calorie-burning muscle you lost on the cleanse will be much harder to regain. Here are signs you might be drinking too many calories.

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You're putting your body at risk

The bottom line is that juice cleanses are unhealthy—whether you're trying to lose weight or jumpstart a clean diet. "I would never recommend a juice cleanse for health benefits. There's no scientific evidence that a juice cleanse is healthy, and by nature, they're too restrictive to be good for the body," says Dr. Auriemma. Adding fresh squeezed fruit and vegetable juices to a balanced diet of lean protein, whole grains, and plenty of whole produce is a much healthier approach to weight loss or maintenance. These are the best superfoods for losing weight.