How To Do A Juice Fast Or Cleanse The Right Way, According To A Nutritionist

Written by Molly Knudsen, M.S., RDN

Molly is a registered dietitian nutritionist who holds a bachelor’s degree in nutrition from Texas Christian University and a master’s degree in nutrition interventions, communication, and behavior change from Tufts University.

Image by Tatjana Zlatkovic / Stocksy

What do you do when you really want to switch things up in your life? Chop all your hair off? Move to a new city? Do a juice fast?  

Many people opt to try juice cleansing or fasting as a way to change their diet's status quo with hopes of jump-starting their way toward better health, weight loss, and improved gut health. But is following this liquid diet effective or even safe? 

Here, we unpack everything you need to know about the benefits and side effects of juice fasting, and the safest way to do it.

What do most juice fasts and cleanses look like?

A juice fast, also known as a cleanse or detox, usually entails drinking DIY or premade juices made from vegetables, herbs, and fruit (and occasionally nut milks, like cashew milk containing whole blended cashews) in addition to ample water, tea, and sometimes clear broths. Juicing fruits and vegetables is different from blending because it isolates the liquid of the produce from the pulp and fibrous portion. Therefore, fruit and vegetable juices will have a more concentrated amount of vitamins, minerals, and phytochemicals but less fiber when compared to something like a smoothie. Juice fasts can be as short as 24 hours or as long as 10 days.

The benefits: Can juice fasting really help you lose weight, detox, or improve digestion? 

Juice fasting has many touted benefits that include reducing inflammation, improving sleep, clearing skin, promoting weight loss, ridding the body of toxins, and reducing sugar cravings. But are these juices really worth the hype? Most of these claims are unsubstantiated and anecdotal rather than science-based, but there may be some positives to note from short-term juice fasting.  

Only one study to date has investigated the effects of a juice fast on health. This study looked at how a three-day fruit and vegetable juice fast affected the gut microbiota, weight loss, and body composition of 20 healthy people. During the fasting period, people drank six 16-ounce bottles of juices that were a mixture of leafy green vegetables, roots, citrus, cayenne, and vanilla almond, totaling around 1,310 calories per day. After the fast, people could then resume their normal diet for two weeks. 

The results showed that people lost a significant amount of weight during the juice fast, and that weight loss persisted over the following two weeks (potentially due to changes in their gut microbiota). However, the weight loss may have resulted from lower calorie intake in general rather than from the juice specifically, and beneficial changes in people's gut microbiota may have been due to the overall increase of fruits and vegetables in the diet for those three days.  

So basically, this study shows that a juice fast of this composition and calorie count for up to three days is safe and can be somewhat beneficial. But those benefits can't necessarily be fully attributed to the juice itself. 

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Potential side effects

There are quite a few downsides to and side effects of juice fasting and cleansing, which is why many health professionals like dietitians and doctors don't recommend it—especially if a cleanse consists of fruit-only juices.

  • You may experience headaches and fatigue: Juices are higher in sugar and lower in fiber than whole foods, leading to a greater likelihood of spikes and dips in blood sugar. Some people say that headaches from juice fasting are due to the toxins leaving your body, but fluctuating blood sugar, in addition to the lower energy intake from the lack of protein and fat in the juices, are actually the root cause of headaches and fatigue.
  • You may feel socially isolated: Think about it; if you're wanting to do a longer juice cleanse of 10 days or so, that's 10 days when you'll be going to lunch with co-workers and won't be able to eat. That could be multiple dinners out when you can only sip on water. 
  • They can be seriously expensive: Juice fasts can be quite expensive, especially if you buy a pre-formulated cleanse. A three-day juice cleanse will often run you anywhere between $99 and $195. That would probably buy you two weeks' worth of groceries!
  • They can be difficult to maintain: All of these factors make juice fasts hard to maintain, even for just a day. And for some people, juice fasts can encourage a type of restrictive eating that may promote an unhealthy relationship with food.   

The best way to do a juice fast to minimize side effects.

If you want to juice fast (despite the potential cons), what's the best way to do it? Here are some tips I'd recommend for before, during, and after your juice fast/cleanse to minimize side effects and maximize benefits:

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Related Class

Before your juice fast.

Before you start a juice fast, take a moment to think about why you are doing this and set realistic expectations. Is it to lose weight? Curb sugar cravings? Reset your digestive system? Whatever your goal is, a juice fast may be a step in helping to reach that goal (depending on what your current eating habits are like), but it is not a fast track to wellness. Making sustained changes to your health and well-being takes time. 

Additionally, you'll want to think through when works best in your schedule to actually start a juice fast. My advice: Plan it for a low-key weekend at home where you can run to the bathroom as often as you need to (you will be peeing a lot!). Juice fasts require you to drink a lot of juice that is perishable, so it may not be best to juice fast when you're traveling either.

During your juice fast.

1. Aim to drink this much juice per day.

During a juice fast, you should aim to drink at least six 16-ounce servings of juice. That works out to one serving of juice every two hours from 8 a.m. to 6 p.m. You can also drink as much water and herbal tea as you want throughout the day. Adding one or two more servings per day is OK if you feel like you need more sustenance. This amount of juice is necessary to get enough calories so you are still meeting (or close to meeting) your body's basic energy requirements.   

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2. Make your juice with mostly veggies.

Aim to make most juices 80% veggies. That means 13 out of 16 ounces (or at least 1.5 out of 2 cups) of juice should be from vegetables. Good veggies to include: spinach, kale, cucumber, zucchini, carrots, beets, and celery. Good fruits to include: lemons, limes, blackberries, raspberries, blueberries, dark cherries, and kiwis. These fruits have lower sugar content and are loaded with anti-inflammatory antioxidants. For a boost of flavor, also consider adding in nutrient-packed herbs such as ginger root, turmeric root, basil, parsley, cilantro, and mint.

Here are two juice recipes to get you started: 

Cool Cukes Green Juice

  • 1 English cucumber, with skin
  • 1 cup spinach
  • 1 small or medium apple, with skin
  • ½ to 1 inch ginger root, peeled
  • Add a squeeze of lemon juice at the end

Berry & Beets Antioxidant Juice

  • 4 red beets
  • 4 medium carrots
  • 1 cup blackberries
  • ¼ cup fresh basil leaves

*Just run each fruit and vegetable through a slow juicer one at a time and enjoy. If you don't have a juicer, simply blend all ingredients and strain with a mesh sieve or cheesecloth (here's how).

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3. Don't feel bad if you have to add in some solids.

For a little more staying power, some people like to add in something with a bit of fat and/or protein. If you find yourself super hungry, consider including one serving of homemade cashew milk per day of your cleanse. You can also make one of your juices a smoothie instead or include a serving of celery and nut butter. There's nothing wrong with adapting your juice fast to meet your needs.

4. Avoid strenuous physical activity.

It would be a good idea to not participate in any strenuous physical activity (think HIIT workouts) during a juice fast, as you could become dizzy and fatigued more easily. And if you are constantly feeling tired, loopy, unable to concentrate, or your hunger pangs are taking over, it may be a sign that your juice fast is doing more harm than good. At this point, consider returning to a whole food diet.

5. Consider stopping after three days.

Research shows that it is completely safe for healthy people to participate in a juice fast for up to three days and then return to a regular diet. Doing a juice fast for a longer period of time can increase the likelihood of experiencing the negative side effects of juicing such as headaches, hunger, and blood sugar swings, and there is no proof of benefit of increased "detoxification" with a longer fast. 

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After your juice fast.

The first day after a cleanse, try eating smaller meals and snacks throughout the day, as a large meal might make you feel nauseous and uncomfortable. Salads, oatmeal, sweet potatoes, and whole fruits could help ease you back into solid foods again, but if you don't have a sensitive stomach, you may be able to resume eating your normal diet right away. After this short introductory period back to solid foods, it is important to incorporate high-quality nutritious foods back into the diet. Whole fruits and vegetables will add more fiber back into your diet. Whole grains like brown rice and quinoa, and protein-rich foods like lentils, legumes, and high-quality meats and poultry should also be added back to meals and snacks.

Who should NOT try a juice fast or cleanse?

There are several groups of people who should not participate in juice fasting. Children, adolescents, and pregnant and breastfeeding women need adequate amounts of energy and protein for growth, and juice fasting would not meet those needs. Elite and competitive athletes also have very high calorie needs, and juice fasting would not support that high energy expenditure or contain the nutrients necessary for optimal recovery. Lastly, people with diabetes, kidney disease, or liver disease should steer clear of juice fasting because of having an altered physiological response to food.

Are there better ways to get the purported benefits?

The most prominent health claim related to juice fasting is its potential to help detoxify, but if you have a functioning liver and kidneys, you really don't need to do anything extra besides eating a balanced diet high in whole, minimally processed foods to detoxify your body. You can achieve the purported benefits of juice fasting like weight loss and better digestion by simply adding more fruits and vegetables to your regular diet. Doing this will up your fiber intake, which is good for digestion, and replacing foods like refined carbohydrates with fruits and vegetables can help with weight loss. 

If you like the idea of drinking your fruits and vegetables, try making a smoothie as a meal replacer instead of juice. Smoothies allow more flexibility with the types of food you put it, especially protein-rich foods. Adding dairy or soy products, nut butters, chia seeds, or flaxseed meal to smoothies bumps up the protein and fat content, making that smoothie a filling meal containing everything you need to nourish your body and feel satisfied. 

Bottom line on juice fasts and cleanses.

Juice fasting and cleansing are essentially trendy, fad diets, and most of the reported health benefits of juice fasting are not backed by science. There are better and safer alternatives to juice fasting, like just adding more fruits and vegetables to your daily diet. But if you really want to try a juice fast or cleanse, keep the tips above in mind to minimize the potential side effects.

Ready to learn more about how to unlock the power of food to heal your body, prevent disease & achieve optimal health? Register now for our FREE web class with nutrition expert Kelly LeVeque.

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