The Truth About Juice Fasts: The Sweet Spot and the Danger Zone

Thursday Mar 19 | BY |
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Healthy Juices

A juice fast may help jolt you into healthier eating, but it can also be dangerous.

They’re trendy. They’re supposed to be healthy. But do they do everything fans say they do?

Turns out that it may depend almost entirely on how many days you stay on the fast. What is the sweet spot for health benefits, and how long is too long?

What is a Juice Fast?

A juice fast, or “cleanse” as some call it, is a diet in which the individual consumes only fresh vegetable and fruit juices. The focus is typically on freshly made, unpasteurized juice (not bottled juices). Most people purchase a juicer and make their own.

The juice fast can last anywhere from a day or two to several weeks, depending on the person and his or her chosen diet or cleanse.

Advertised Benefits of a Juice Fast

Fans of juice fasts say they:

  • Help you lose weight
  • “Reset” the digestive process, reducing problems like bloating and gas
  • Flush “toxins” and other impurities from the body; give the liver a break
  • Help you think more clearly
  • Give you more energy
  • Reduce your appetite
  • Help you break unhealthy eating patterns
  • Flood the body with vitamins, minerals, and antioxidants that help fight disease
  • Encourage optimal functioning of body cells
  • Give you clearer, more radiant skin
  • Reduce problems like headaches, rashes, and general aches and pains

Could just drinking juices for a few days really do all that?

Talk to people who have actually gone through a juice fast and you’ll get a variety of responses. For some, it seems they do provide most of the benefits above, but for others, it’s a different story.

“I woke up on day 3 feeling rested and unaware of the hunger pangs I experienced the night before,” writes Allison Norton, associate editor at “My skin was glowing, my eyes were sparkling, and I felt light and lean.” She adds she gained a “sense of accomplishment” after completing her fast, and that it motivated her to “stay on a healthy path for weeks afterward.”

The experience was a little different for Tracy Russell, creator of a program for energy and weight loss. “I felt amazing during the first two days,” she writes. “Waking up on day two with the feeling of nothing inside my body felt great.”

She also suffered headaches, though, and found making the juices time consuming. “All in all, I enjoyed my 5-day juice fast,” she says. “After completing it, though, I really don’t feel I need another one.”

“I think of it as a voluntary colonoscopy prep without the actual procedure,” writes Linda Flanagan in Huffington Post. She did a juice cleanse with her daughter for one day. “Vaguely queasy and a little grumpy, I consider all the delicious food in the cupboards while my stomach lurches in hunger. When will this day be over?”

Is There Any Scientific Evidence Juice Fasts Work?

Considering the variety of reactions, we may wonder: Have any of the so-called benefits of juice fasting been proven?

I did some research. The truth is, there aren’t very many studies on juice fasts. In fact, I found only one, and it was extremely small.

  • Juice fasting may lower cholesterol temporarily: A small 2003 German study (of only 5 people) seemed to suggest that juice fasts may help lower cholesterol. Researchers had five healthy men drink only 150-300 calories worth of vegetable and fruit drinks for five days. They took blood tests on days 2, 3, and 8 during fasting, and again on days 2 and 8 after fasting. Results showed that after eight days, participants experienced a slight decrease in total cholesterol (9 percent), but one week after the fasting ended, all levels returned to normal, so any potential benefit to cholesterol levels didn’t last.

Look up regular old fasting (without the juice), and you find more science. A 2014 study review, for instance, from the National Institute of Aging, found that intermittent fasting may help prevent obesity and associated modern-day diseases.

But that’s not what we’re talking about here. This post is about juice fasts. Is there any way to tell if they have any true benefits at all?

What a Juice Fast May Do for You

Until we have more studies, we can’t prove that juice fasts do any of the things fans say they do. That means that it’s up to each individual to determine whether drinking only fruit and vegetable juice for one or more days will do any good.

How to do that? We can weigh the pros and cons, based on what we know so far.

The Possible Pros of Juice Fasting

1. Break the cycle of dependence on unhealthy foods.

This is probably the most important benefit of a short-term juice fast. Committing yourself to a diet of only healthy, fresh fruits and vegetables means that for a certain amount of days, you will avoid all the unhealthy stuff. That includes processed foods, refined sweets, junk foods, saturated fats, and high-fat and high-salt items. That one thing alone can make a big difference in your diet and your health, as it acts like a wake-up call.

CrossFit Pacific Coast founder Traver H. Boehm writes about his 10-day juice fast in Breaking Muscle, where he describes days one through three as “pure hell,” but also as eye-opening.

“Eye opening in that as the days went on, I became less and less ‘hungry’ but more and more ensconced in this idea that I needed to eat every 10 minutes or so. My desire to eat…was less about becoming satiated…but more so to satisfy the habit of eating….I simply wanted to put something in my mouth, chew it, swallow it and derive the familiar pleasure from doing so. I am addicted to eating!”

If you can stay disciplined through the first initial tough period of your juice fast (and it will be tough for most people), you, too, may gain an increased awareness into your usual eating habits, and how they may have gotten off track.

A quick, weekend juice-cleanse of no more than three days can help you reset your body and mind and get you back into healthy eating again. You’ll gain insight into when you usually eat, what you eat, and why, and you can then can use that information to improve your habits after the fast is over.

2. Find a way to get more fruits and veggies into your diet.

We all know that fruits and vegetables are good for us, and that we need to get more into our daily diets. Guidelines recommend 5-13 servings a day, depending on your caloric intake, which amounts to about 2.5 to 6.5 cups.

Are you getting that much?

Most of us aren’t. A juice fast can make that abundantly clear, and it can also whet your appetite for more. Once you’ve finished the fast, you may find yourself craving fruits and vegetables in a way that motivates you to eat more of them. Maybe you’ll add more to your meals, or even stick with an added juice on a daily basis.

What about the claim that juice fasts can cure disease? We have no evidence of this, and actually, when taken too long, a juice fast can result in a loss of nutrients. (See below.) It’s best not to count on any extreme diet long-term to cure you of anything. Instead, let the short-term juice fast get you into the habit of buying, preparing, and eating more fruits and vegetables—that’s your best bet for avoiding disease and arming your body with what it needs to stay as healthy as possible.

3. Help you think more clearly.

This one is questionable, but many people have reported this benefit after a juice fast. It probably depends on what sort of diet you were on before starting the fast. If you regularly tanked up on caffeine, sugar, and alcohol, ridding your body of these things may very well help your brain function better, so that you feel like you’re thinking more clearly.

Studies have shown, for example, that sugar can affect brain function. In a 2012 perspective in the Journal of Physiology, the authors referenced a number of studies showing that high sugar intake coupled with a deficiency of omega-3 fatty acids was associated with a lower cognitive score.

If your juice fast helps you break sugar cravings, you may find that it leads to clearer thinking in the future.

The Possible Cons of Juice Fasting

What about all the other supposed benefits? Aren’t juice fasts supposed to help rest and repair the digestive system? Help you lose weight? What about the detox effect?

1. Weight loss may turn into weight gain.

Most people do lose weight on a juice fast, but it’s usually water weight. The danger is that depending on how long you are on the juice fast, when you go back to eating your regular diet, you may gain more weight than you lost.

The problem is that most juice fasts are low in protein. If you fast for more than a few days, your body will start cannibalizing your muscle tissue for that protein, which means when you go back to your regular diet you have less muscle to burn calories. That could result in more of your food being stored as fat.

“[W]ithin three or four days,” Leslie Schilling, R.D., told The Daily Beast, “you’re going to see somebody potentially tap into other stores once their body realizes it’s not getting the energy it needs from sources like fat and protein.” Weight loss can come at the expense of muscle loss.

Prolonged fasting also tends to slow your metabolism. Too many or too long of a juice fast can confuse your body, making it harder to lose weight in the future.

“You can alter your metabolism and slow it down,” Laren Blake, registered dietician with the Ohio State University Wexner Medical Center told US News. “These cleanses cause your body to cling to every calorie because it doesn’t know when it’s going to get its next dose of energy.”

Finally, because the body has a hard time registering liquid calories, you can actually consume more during your juice fast than you usually do without realizing it.

2. Spikes in blood sugar can leave you feeling badly.

Will you feel good on a juice fast?

Maybe not.

Most people don’t consume the pulp from the fruits and veggies, which means they’re getting little fiber. The body doesn’t have to work to digest the juice, so it goes almost immediately to the bloodstream, spiking blood sugar levels. The crash comes a few hours later.

These ups and downs affect the body. Fasters may suffer from headaches, fatigue, irritability, and mood swings.

3. You may have a hard time sticking with the diet for long.

Fiber and protein help keep you satisfied for longer. Most juice fasts are low in these two nutrients, which means they’re likely to leave you feeling hungry. That feeling may get worse the longer you stay on the fast.

A standard juice fast is essentially a high-carb, low-protein, low-fiber, and low-fat diet. Your body also doesn’t register liquid calories as well as solid ones, so even though you may be consuming the same amount of calories as usual (or close to it), you may experience a lot of hunger, even to ravenous levels that make it difficult to stay with the fast.

4. You may experience digestive problems.

Juice fasts are advertised as giving your digestive system “a break.” When you take the fiber out of the veggies and fruits by juicing them, you allow the body to absorb the nutrients without much help from the stomach or intestines.

The truth is, though, that your digestive system operates best when you consume enough fiber. On a juice fast, you consume a lot of liquids, but often little to no fiber. That can result in diarrhea because of the excess liquid (which many people experience on a juice fast), as well as constipation over time, as the digestive system has no fiber to help absorb and move waste.

In addition, a lot of fruits like pears, sweet cherries, peaches, and apples, have a natural sugar called “sorbitol” that can cause bloating and gas. If you add a lot of these types of fruits to your juices, you could experience more digestive discomfort than usual.

5. You will likely feel tired.

If you’re doing just a weekend juice fast, you can take your time and rest and enjoy the experience.

If you go longer than that, prepare to be tired. Too tired to exercise, which can actually derail your health and weight-loss goals.

“[A]fter a hard workout,” says Boehm, “I would find myself for all intents and purposes feeling mildly drunk.” When symptoms like forgetfulness and dizziness got worse, he added foods back to his diet, including protein-rich eggs and healthy-fat-filled avocados.

Natalie Jones, spokesperson for the British Dietetic Association, seconds this opinion on juice fasts and exercise. “You might be getting a quick sugar rush,” she tells the Daily Mail, “but you’re not consuming any carbohydrates, so exercising, or even normal daily life is going to be almost impossible. You’ll feel light-headed and exhausted.”

Cynthia Sass, R.D. and sports nutrition consultant to the New York Rangers, adds, “doing both exercise and a cleanse can leave you feeling tired, dizzy, and nauseous. It can also result in breaking down muscle mass, which can up your injury risk and lower your metabolic rate, the exact opposite result of what you’re aiming for.”

6. Don’t count on a detox—you may even suffer from a lack of key nutrients.

So far, we don’t have any evidence showing that juice fasts reduce internal toxins. Most health experts, including doctors and scientists, will tell you that our kidneys and liver do just fine at ridding the body of waste and that they don’t need any help.

“Your body does a perfectly good job of getting rid of toxins on its own,” says Dr. Nasir Moloo, gastroenterologist in Sacramento, California.

Like a colonic, a juice fast may help flush out your system, but does that really get rid of any chemical buildup in the body? We don’t have any studies showing that it does, so it’s hard to tell.

In addition, realize that as long as you are on the juice fast, your body is likely missing some important nutrients, like vitamin D, calcium, protein, and essential fats. Longer fasts can also lead to electrolyte imbalances (potassium and sodium).

7. It may lead to foodborne illness.

Raw fruits and vegetables may be contaminated with bacteria, which if not handled correctly, could lead to foodborne illness.

Juicing alone doesn’t kill these pathogens, and the longer you store the juice, the more time the bacteria have to grow. Foodborne illness can result in unpleasant symptoms like vomiting and diarrhea. Women who are pregnant or breastfeeding are especially at risk, as well as those with autoimmune diseases.

Proper cleansing of the produce before juicing helps, as does drinking it right away.

8. It’s likely to make your skin and hair worse.

Healthy fats are critical to good-looking skin and hair. A juice fasts rarely gives you enough (if any). Over time, that can dry out your skin and hair, and may even damage the outer layer, increasing risk of eczema. If you juice for longer than a few days, you may notice increased hair loss, dryness, and accelerated signs of aging like wrinkles and fine lines.

Without these fats, the body also has a hard time absorbing fat-soluble vitamins like vitamin A, D, E, and K. Keep in mind, too, that if you add too many items rich in carotenes (think yellow fruits and veggies like carrots, cantaloupe, and apricots) your skin could actually take on a yellow tinge.

9. It may damage your teeth.

Juices are high in acid from both fruits and vegetables, which can wear down the enamel that protects your teeth. (Read our post about the raw food diet and teeth.)

“Juice from vegetables and especially from fruits,” says Dr. Uchenna Okoye of London Smiling, “which tend to have a higher acid content, can damage the enamel of your teeth in exactly the same way that a fizzy drink would.”

Even though fruits have natural sugars, these can still feed the bacteria in the mouth, and may increase the risk of cavities and gum disease.

10. It could be dangerous for some populations.

Juice fasts can be dangerous for certain populations, including diabetics (because of the blood sugar spikes), the elderly (who may already be low in nutrients), children and teens (because nutrients affect growth and development), and those going through chemotherapy treatments (who need things like fiber, protein, and other nutrients to help the body withstand the drugs).

Tips to Help You Enjoy a Successful Juice Fast

Being aware of the previous 10 potential problems can help increase your odds of enjoying a healthy, feel-good juice fast. If you’re still game on trying one, consider the following tips to increase your odds of experiencing the health benefits you want.

  • Keep it short: Limit your fast to 1–3 days—this seems to be the “sweet spot” for enjoying the benefits without causing additional problems.
  • Pain isn’t gain: Listen to your body and mind—if something doesn’t feel right, stop. You can always try the fast again at another time.
  • Choose the right time: Conduct the fast on a weekend or during a time when you don’t have a lot of expectations on you. You want to be able to relax and rest.
  • Wash everything: To reduce risk of pathogens, wash everything before you juice it. Drink the juice the same day, and always wash your juicer after each use with warm water and soap.
  • Keep an eye on sugar content: Fruits taste good in juices, but they have a higher sugar content than veggies. Try to use juicing recipes that include more veggies and less fruit to keep your sugar content under control.
  • Add protein and fiber: Some people don’t like to do this because they want to give the digestive system a break. If you find yourself suffering a lot of hunger or cravings, though, feel free to add in some fiber and protein through powders, flaxseeds, yogurts, nut milks, hemp seeds, pulp added back in, and other ingredients.
  • Start out feeling strong: During an illness is not the best time to start a juice fast. Instead, choose a time when you’re feeling healthy and strong, or at least well rested and free of illnesses.
  • Protect your teeth: Use a straw to consume your juice, and don’t brush for at least an hour afterwards. (The acid weakens enamel, and brushing will make it worse if you do it too soon.) You can rinse with water afterwards to cut down on bacteria in the mouth, and you can also brush before drinking your juice if you like.

Have you tried a juice fast? How did you feel while you were on it? Did it have the health benefits you hoped for?

* * *

Linda Flanagan, “The Secret Ingredient of the Juice Cleanse: Nausea,” Huffington Post, March 29, 2012,

Tracy Russell, “My 5-Day Green Juice Fast Experience,”

Allison Norton, “Detox Diary: My 3-Day Juice Cleanse,”, January 29, 2013,

Huber R, et al., “Effects of one week juice fasting on lipid metabolism: a cohort study in healthy subjects,” Forsch Komplementarmed Klass Naturheilkd, February 2003; 10(1):7-10,

Mark P. Mattson, “Meal frequency and timing in health and disease,” PNAS, November 24, 2014; 111(47):16647-16653,

Traver H. Boehm, “10 Day Juice Fast: What Does it Feel Like?”,

Jill N. Barnes and Michael J. Joyner, “Sugar highs and lows: the impact of diet on cognitive function,” The Journal of Physiology, June 2012; 590(12):2831,

Kate Parham, “Is a Juice Cleanse Good for You?” Real Simple Magazine,

Amir Khan, “Juice Cleanses: Health Hocus Pocus,” US News, June 6, 2014,

Cord Prettyman, “The Dangers of Juice Fasting,” Pikes Peak Courier, January 27, 2012,,129004.

Claire Coleman, “Juicing can wreck your looks: Flaking skin, hair loss and rotting teeth. The latest A-list diet crazy has some ugly side-effects,” Daily Mail, July 4, 2012,

Kristen Domonell, “Is Your Juice Cleanse Doing More Harm Than Good?” The Daily Beast, February 11, 2014,

Colleen M. Story

Colleen M. Story

Colleen M. Story, a northwest-based writer, editor, and ghostwriter, has been creating non-fiction materials for individuals, corporations, and commercial magazines for over 17 years. She specializes in the health and wellness field, where she writes and ghostwrites books, e-books, blogs, magazine articles, and more.

Colleen is the founder of Writing and Wellness. Her fantasy novel, “Rise of the Sidenah,” was released with Jupiter Gardens Press in September 2015. Her literary novel, “Loreena’s Gift,” is forthcoming in spring 2016 from Dzanc Books. She lives in Idaho.

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