Does Juice Fasting Work? What Nutrition Experts Need You to Know
Weight loss is one of the main reasons people try a juice fast, but this juice cleansing trend comes with health risks. Here's what the experts say.
Is juicing good for you?
It’s no secret: It’s smart to eat fruits and vegetables as part of a healthy diet to help lower your risk of chronic health conditions. However, some people try to drink their fruits and veggies by juicing, or consuming juice instead of the whole foods.
Others try juice fasting, where they limit food in general and consume only juice for a period of time.
People turn to juice fasts for various reasons, but usually for weight loss or an attempt to detoxify the body. But is it safe and healthy? Most nutritionists warn that juice fasting comes with some serious health risks and dubious benefits.
Juice fasts or juice cleanses involve consuming only juices from vegetables and fruits for a set period of time. “Juicing takes the pulp out of fruits or vegetables with a juicer, leaving many of the vitamins, minerals, and plant compounds,” explains Erika Laurion, a nutritionist in Hudson, New York.
Juice fasts can vary in terms of how long they last and the juices they include. Some only allow vegetable juices while others are fruit juice-based; others combine fruit and veggie juices for the fast. Popular juices include celery, beet, and spinach juice.
“Juices are not smoothies. They don’t have other ingredients,” Laurion stresses. There are many kits available that explain juice fasting and provide the juices, while in some cases people prepare the juice on their own.
Here’s what you need to know about juice fasting, its purported health benefits, and risks, according to our panel of health experts.
Juicing and juice fast methods
One approach is to do a juice fast just for one day each week on a semi-regular basis. This is a type of intermittent fasting.
People who do juice fasts usually opt to make their own juices at home or buy a pre-packaged cleanse online or at a health food store. Ambitious do-it-yourself juicers need to purchase a juicer. DIYers will also need to buy a lot of produce. It actually takes 6 to 8 large carrots to make one glass of juice, according to the National Center for Health Research.
There are two main types of juicers, explains Laurion. The centrifugal juicers use a high-speed spinning action to grind fruits and vegetables with a cutting blade. The spinning also separates the juice from the solids.
Cold-press or masticating juicers crush and press fruits and vegetables. These work more slowly than centrifugal juicers.
Laurion uses the centrifugal juicer, still, some prefer cold-pressed juicers. “They may say centrifugal juicers are not as pure as the cold-pressed because they might be creating heat and friction that could damage they nutrients in the fruit,” she says. This does not occur with cold-pressed juicers.
Calories and juice fasting
Calories vary based on the type of juice as well as what else is consumed during a juice fast, Laurion says. Some juice fasts may allow you to eat whole fruits and veggies too.
Ten ounces of carrot-apple juice contains 200 calories, while the same amount of spinach–cucumber–celery juice has 139 calories, according to recipes from Stanford University.
In general, most juice fasts total up to 1,000 calories per day.
What are the risks of a juice fast?
Experts caution that there are potential health risks to juice cleanses or fasts.
In general, juice fasting—like many other types of fasting—can cause fatigue and irritability. Another risk is diarrhea as juices can act like natural laxatives because sugars stimulate the gut to expel water and electrolytes.
Lastly, keep in mind that some people who should not attempt a juice fast, says Liz Weinandy, RDN at the Ohio State University Wexner Medical Center in Columbus, Ohio.
“People who are elderly or frail, growing adolescents and women who are pregnant or breastfeeding need more nutrients than these fasts provide,” she says. “Fasting is not advised if you have a history of eating disorders or disordered eating.”
Although some fans of juice fasts cite the lack of fiber as a positive, Weinandy says it is actually one of the risks.
“Besides staying regular, fiber feeds the beneficial or good microorganisms found in the gut, helping to maintain a healthy gut microbiome balance,” she says. When the bacteria is out of balance, you may feel bloated, be constipated, have diarrhea, or experience many other digestive ills. A well-balanced gut microbiome is believed to aid weight loss efforts and boost the immune system’s ability to ward off diseases.
The recommended amount of dietary fiber is 20 to 35 grams per day. Most people fail to hit this mark as it is, according to the Academy of Nutrition and Dietetics. (Here are some sure signs that you are not getting enough fiber.)
“Juices don’t have protein, which keeps you full and helps you maintain muscle mass,” Weinandy says. “If you go more than a few days without protein, fiber, and other nutrients that are not found in the juices, you can develop deficiencies,” Weinandy says. The longer the fast, the greater the risk for these shortfalls, she adds.
Juices should not be used as a meal replacement to encourage weight loss, stresses the National Center for Health Research. This can be harmful over the long term as juices can slow your metabolism because they lack protein and fat.
High blood sugar
Many juice fasters prefer fruit juices instead of vegetable juices because they taste better, says Weinandy.
This can be risky if you have diabetes, because juice can raise your blood sugar really quickly, she adds. The fiber is gone and it’s the fiber that slows the rate of absorption,” she explains. “This can cause blood sugar to soar.” If you have diabetes, talk to your doctor before trying any fast, including a juice fast.
Some of the juices in cleanses haven’t been pasteurized to kill bacteria, which can make you really sick, especially if you have a weakened immune system, the National Center for Complementary and Integrative Health warns.
How can you tell? “Raw” is a clue, the FDA warns. If fruits and vegetables are fresh-squeezed or used raw, they are not pasteurized and bacteria can end up in your juice.
Juice fasting may also increase risk for developing painful kidney stones, as some of the fruits or veggies used in juices are high in oxalates such as spinach and beets. Overdoing it on oxalates can increase the risk for kidney stones.
Potential health benefits of juicing
Rest your gut
Fruits and veggies are excellent sources of fiber, which improves your digestive health, improves cholesterol, and has loads of other health benefits. But the juicing process removes fiber.
Fiber takes a lot of energy to digest, so juice fasts may give your system a much-needed respite, Laurion says. “It gives a break to your body because it uses less energy to digest food and it can use that energy elsewhere to promote healing,” she says.
More fruits and vegetables
If you don’t get enough fruits and vegetables in your diet (and most of us don’t), juicing is one way to do it, says Weinandy.
However, you’re not getting the same nutrients that you get from whole fruits and vegetables because so many of them are in the skin or the flesh of the fruit.
Fans of juice fasts claim they help detoxify or remove unhealthy substances from your body, but this is a myth, Weinandy says.
“Our bodies and livers are all we need to detoxify,” she says. “The best way to detox is to eat whole foods and a mainly plant-based diet. It doesn’t have to be anything outlandish like drinking only juice for 10 days.”
What you don’t eat matters too when you are attempting to get rid of the toxins. “Avoid highly processed foods with preservatives,” she says.
Juice cleanses may produce weight loss, Laurion says.
When 20 healthy adults went on a three-day juice fast consisting of six bottles of fruit/vegetable juice blends per day, they lost between 3 and 4 pounds, and this weight loss was maintained over the following two weeks. The study appears in Scientific Reports. The study authors also noted that juice fasting also decreased lipid oxidation and increased nitric oxide levels, which may lead to improved heart health.
On the other hand, drinking a lot of juice can also cause weight gain and it can be dangerous for people with diabetes because of the concentration of sugar and calories. Even if you do lose weight, you are likely to gain it back, experts say.
Juicing—not juice fasts—provides more fluid to help keep your body hydrated, which can help your kidneys do what they need to do, the National Kidney Foundation notes. What’s more, the extra antioxidants from the fruits and vegetables may cool inflammation, which can be an aggravating factor in kidney disease.
Still, the foundation cautions, people with kidney disease or decreased kidney function may need to limit fluids and certain nutrients, such as potassium, Many juicing recipes contain fruits or vegetables that are high in potassium, and juicing can increase the concentration of such nutrients.
Some juicing recipes also use canned tomato or vegetable juice which can be high in sodium and can further tax damaged kidneys.
The last word
Juicing may seem like a quick and easy way to get your daily servings of fruits and vegetables. However, the best way to get those nutrients is through whole foods, such as eating an orange or adding a cup of broccoli to your meals. Also, there’s no evidence that juice fasts actually detox the body.
As always, check with your doctor before changing your diet drastically for more than a couple of days. Remember, juiced fruits and vegetables don’t have protein, fiber, and many important nutrients your body needs.
- Erika Laurion MS, CDN, CNS, a dietitian in Hudson, New York
- Liz Weinandy, MPH, RDN, LD, a dietitian at the Ohio State University Wexner Medical Center in Columbus, Ohio
- Scientific Reports: "Health benefit of vegetable/fruit juice-based diet: Role of microbiome"
- National Kidney Foundation: "To Juice or Not to Juice?"
- Academy of Nutrition and Dietetics: "Easy Ways to Boost Fiber in Your Daily Diet"
- National Center for Complementary and Integrative Health: "'Detoxes' and 'Cleanses': What You Need To Know"
- U.S. Food and Drug Administration: "What You Need to Know About Juice Safety"
- Stanford University Health Care: "Juicing Recipes"
- National Center for Health Research: "6 Things You Need to Know About Juicing Your Veggies"
- Harvard Health Publishing: "Juicing -- Fad or Fab?"