Presented By
Danny Kim for TIME

Ah, the start of a new year! Gym memberships suddenly spike, bathroom scales get dusted off, and friends start discussing which juice cleanse to try. We are 100 percent on board with this uptick in well-intentioned motivation—but we think it’s important you always know what you’re getting into.

First thing’s first: Juice cleansing is a “detox” diet that can last from a few days to several weeks in which a person consumes only fruit and vegetable juices to obtain nutrition while otherwise abstaining from eating food. Many people swear by cleanses and report an improvement to their health, mood, and appearance. The scientific community, however, is less than enthusiastic about juice cleanses—many scientists, dietitians, and doctors regard detox diets as less effective than fasting with water, and, therefore, a waste of money. That said, if you’re going to do one anyway, we recommend consulting with your doctor—or at the very least going along with an “official” juice cleanse program. Simply drinking any ol’ juice from anywhere around town is not a good idea.

Now for the nitty gritty. We enlisted the help of several nutritionists to get a feel for the kinds of things that can happen to the human body when embarking on a juice cleanse. What they came back with is essential reading for you or anyone you know who is thinking about being the conspicuously abstaining-from-food friend for a few days. If you get through the list and decide maybe you’ve changed your mind, consider jump-starting your weight loss with our brand-new book Zero Belly Smoothies instead—or gulp down some detox water on the way home from your shiny new workout digs.

1. Your metabolism will slow

Once you stop eating enough food to meet your basic energy requirements, your metabolism will slow. For most people, that threshold of calorie intake is around 1,200 calories per day. “Your body goes into conservation mode because it doesn’t know when its next meal is going to be,” says nutritionist Ilyse Schapiro, founder of She reminds us that, even though cutting calories will lead to weight loss, going too low for too long can have the opposite effect. It’s one of the biggest takeaways on the list of 25 Things You’re Doing to Slow Your Metabolism!

2. You can discover what ails you

Since most juice cleanses eliminate dairy, wheat, gluten and fermented foods from your diet, you can gain a new perspective on whether any of these foods don’t agree with your body. “[Eventually] reintroducing them can help define which foods are causing problems for your body,” says Dr. Woodson Merrell, Chairman of the Department of Integrative Medicine, Beth Israel Medical Center and Author of The Detox Prescription.

3. You’ll be sensitive to cold temperatures

So far, it’s been an exceptionally warm winter for many people—but there’s no telling when our old friend the polar vortex might decide to show up. Winter isn’t a great time to start a juice cleanse because many people do look to hot foods and beverages to help maintain body temperatures during the colder months. Picture it: When it’s 20 degrees outside, a hot tea for weight loss may be a better choice than a cold pressed juice.

4. You may lose your spark

When consuming only fruits and vegetables via a juice cleanse, there is a decrease in the amount of calories being consumed regularly. “The body requires enough calories to be used as energy for normal body functions,” says Jim White, owner of Jim White Fitness & Nutrition Studios. “Without enough calories and energy, you could feel weak, have headaches, or have low energy.”

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5. You may experience caffeine withdrawal

If you’re fully committed to your juice cleanse, that means you’ll have had to cut out all caffeine. “Even if you normally drink only one cup a day, eliminating caffeine cold turkey may contribute to headaches, irritability, and difficulty with concentrating,” says nutritionist Amy Shapiro, founder of Even if you think you’ll have a different sort of energy from your juice, What Happens to Your Body When You Drink Coffee is a different experience.

6. You’ll drop water weight

Plenty of water is locked up in your muscles with glycogen. “When you eat a low-calorie diet, you use up those glycogen stores, and you lose the water weight with it,” says’s Seth Santoro. The excitement is temporary, though; Santoro adds that you’ll gain that water weight right back when you return to your normal diet. For non-cleansing ways to get rid of belly bloat, find out the 24 Ways to Shrink Your Belly in 24 Hours!

7. You may feel lightheaded

Whether its made from fruit or vegetables, the juice you’re drinking on a cleanse contains a high amount of sugar. “That will cause your body to produce insulin faster, making your blood sugar drop,” says nutritionist Leah Kaufman, founder of “This results in dizziness and feeling lightheaded.”

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8. Your skin can dry out and age more quickly

When eating a low-calorie diet, water stored in your muscles with glycogen gets used up—which causes your skin to feel dry. “Balance is the key,” says Antonia Burrell, associate lecturer in the chemistry of aromatherapy at the London College of Fashion. Burrell says that a prolonged juice cleanse can lead to a drier skin and potentially prematurely-aged skin because of the lack of essential fatty acids being consumed. Yikes! For more ways food and drink can cause wrinkles, check out the 20 Foods That Age You 20 Years.

9. Your appetite may calm down

Although juicing doesn’t actually shrink the stomach, it does temporarily eliminate the possibility to eat for comfort. The upshot of that is that you will feel satiated with less food than usual, immediately after you’re done with the cleanse. This situation can provide a big psychological boost that some people need to experience so that they can change their eating behaviors and stop sabotaging their weight loss.

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10. Your hair and nails won’t grow

When you’re on a juice cleanse, you’re not eating a diet that contains all of the nutrients found in a balanced diet. That will some significant consequences but one change you’ll notice first is that your hair and nails aren’t growing as quickly. “Protein, fats and carbohydrates. We need all of these for healthy skin, hair and nails,” says I. Schapiro.

Read the full list HERE. This article originally appeared on Eat This, Not That!

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