Juice fasts have gained popularity as a quick way to lose weight, clear toxins, and improve skin condition. However, it's essential to examine both the potential benefits and risks associated with this practice. Juice fasting involves limiting consumption to only fruit or vegetable juices for a period, typically ranging from three to ten days, while abstaining from solid foods.
What is Juicing and Juice Cleansing?
Juicing is the process of extracting juice from fruits and vegetables, usually discarding the pulp and skin. Juice cleansing, on the other hand, is a specific type of short-term detox diet that involves consuming only fruit or vegetable juices. Some believe this process detoxifies the body.
Potential Benefits of Juice Fasting
While many people turn to juice fasts with the hope of experiencing various health benefits, it's important to approach these claims with a critical eye. While fruits and vegetables are indeed rich in beneficial compounds, the way they are consumed can impact their effects on the body.
Juicing for Health
Fruits and vegetables are packed with active compounds that promote overall health and help prevent chronic diseases. They are a good source of phenolic compounds, which possess antioxidant, immune-supporting, and antibacterial properties. Fruit juices may also contribute to lower blood pressure and cholesterol levels. In addition, the bioavailability of vitamin C, flavonoids and other useful phytochemicals is increased by juicing.
Juicing for Weight Loss
Juice cleanses may lead to weight loss. A 2017 study revealed that a 3-day juice-only diet altered the gut bacteria in participants, resulting in substantial weight losses that lasted after the study ended. The researchers suggested that these changes in gut bacteria may be responsible for the weight loss.
Read also: 7-Day Juice Cleanse
However, this study also noted that participants consumed only 1,310 calories per day, which is below the recommended daily calorie intake for adults. Therefore, being in a calorie deficit could lead to rapid weight loss regardless of whether it is achieved through juice cleanses or other means.
Juicing for 'Detox'
Some detox treatments have been shown to improve liver detoxification and remove environmental pollutants from the body. However, a 2015 review suggests that clinical studies on this topic often have methodological flaws and low participant numbers. Much of the evidence also comes from animal research, which may not be applicable to humans.
Juicing for Skin Health
Some studies suggest that consuming fruit juices may improve skin health by reducing inflammation and oxidative stress. However, these are both animal studies and more research with humans is needed before any conclusions can be drawn.
Risks and Downsides of Juice Fasting
Despite the potential benefits, juice fasting also carries several risks and downsides that need to be considered.
Insufficient Nutrient Availability
Juice cleanses often don't provide enough nutrition. Most people who do juice cleanses don’t eat enough solid food to meet their energy needs. This may lead to increased hunger and energy restrictions that could cause symptoms like tiredness, headaches, and irritability.
Read also: Explore the pros and cons of fruit juice detoxes.
Fruit and vegetable juices have virtually no protein and are very low in calories. While that can promote weight loss, it’s mainly because you’re losing water and muscle. When you resume your usual eating habits, you’re likely to regain weight lost during a short-term fast, according to the Mayo Clinic.
High Sugar Intake
Pureed juice drinks contain a lot of sugar, in the form of glucose, and lack fiber. This leads to many individuals feeling hungrier than usual, as their blood sugar levels spike and then drop. Blood sugar spikes can cause brief spurts of energy followed by slumps, manifesting as tiredness, headaches, and irritability.
Fruit juice is very high in sugar, which can cause high blood sugar in someone with diabetes or prediabetes.
Reduced Fiber Intake
Juices have less dietary fiber than whole fruits and vegetables. While some research suggests that less fiber facilitates your body to process and absorb the juice’s nutrients, dietary fiber also has many health benefits. It promotes blood sugar management, heart health, and gut health and is associated with a reduced risk of developing colorectal cancer.
A study published in 2025 found that juice diets lacking in fiber caused harmful changes to oral and gut bacteria after just three days. Meanwhile, low fiber intake could slow down your digestion, causing constipation.
Read also: Juice Cleanse: Benefits and Risks
Loss of Muscle Mass
Many studies have shown that lack of protein leads to the person not feeling full, creating a psychological pressure to eat more. In addition to the temptation to eat something rich and filling, there is also a loss of muscle mass due to the protein deficit, which means that after the diet the weight is regained. It’s important to note that after a few days of juice cleansing, you may also start to lose muscle mass. Maintaining muscle mass during weight loss is very important for your general health.
Potential for Eating Disorders
Juicing may increase the risk of eating disorders. For example, an obsessive preoccupation with health-promoting foods and an avoidance of foods considered “less healthy” can lead to orthorexia nervosa.
Kidney Health Concerns
Some foods are high in oxalate, a compound that can increase a person’s risk of kidney problems when consumed in high quantities. Foods high in oxalate include spinach and beets.
People living with chronic kidney disease may be at risk of oxalate nephropathy. In rare cases, healthy people may also be at risk of this. Oxalate nephropathy is a condition in which the body cannot excrete enough oxalate through urine, causing it to build up in kidney tissue. In rare cases, this can cause kidney failure.
Lack of Scientific Evidence for Detoxification
Scientific evidence doesn’t support juicing’s claim to detoxify the body or individual organs. The digestive system is self-cleaning and naturally removes toxins. The liver and kidneys remove toxins and waste. According to the University of Rochester Medical Center, your kidneys and liver do that job 24/7, so the best way to remove toxins is to support these organs with a healthy, balanced diet high in whole fruits, vegetables, and other high-fiber foods, and low in salt and added sugars, especially in ultra-processed foods and alcohol.
Social Isolation
The restrictive nature of a 21-day juice fast could mean three weeks of difficulty socializing over meals. During this time, you might lose out on the pleasure of enjoying food with others.
Juice Fasting and Weight Loss: A Closer Look
While juice fasts may lead to initial weight loss, it's essential to understand the nature of this weight loss and its long-term sustainability. A juice fast is not the best way to lose weight.
Water Weight and Muscle Loss
It’s possible to lose weight on a juice cleanse. However, this is likely to be water weight, rather than fat.
Fruit and vegetable juices have virtually no protein, and are very low in calories. While that can promote weight loss, it’s mainly because you’re losing water and muscle.
Unsustainable Weight Loss
Rapid weight loss isn’t usually lasting weight loss. Though a juice fast might melt away pounds quickly, it’s not a long-term solution - and could lead to a cycle of yo-yo dieting. Severe caloric restriction is not sustainable for most people and rarely leads to long-term weight loss. In most cases, a person will return to their starting weight quickly once caloric restriction ends.
Alternatives to Juice Fasting
For those seeking to improve their health, lose weight, or support their body's natural detoxification processes, there are several evidence-based alternatives to juice fasting:
Balanced Diet
Eating a balanced diet and staying adequately hydrated are the best ways to maintain a healthy weight and support the body’s removal of toxins.
Plant-Based Diets
Based on minimally processed foods, these diets are naturally rich in fruit and vegetables and are associated with reduced body weight. With good planning, a plant-based diet can provide all the nutrients necessary for good health.
Intermittent Fasting
This involves abstaining from eating for limited periods and eating a regular diet at other times. Reviews have linked intermittent fasting with weight loss and improvements in insulin sensitivity.
The 21-Day Juice Fast: A Detailed Examination
The 21-day juice fast is a more extended version of the typical juice cleanse, often involving a phased approach to reintroduce solid foods.
How the 21-Day Juice Cleanse Claims to Work
Some 21-day plans (usually those promoted by juice companies) recommend fruit and vegetable juices only for 21 days. However, most plans suggest juices for up to one week, followed by a week of vegetable soups and smoothies, followed by raw foods, but no meats or animal foods, to gradually get your digestive tract working again.
People may choose to adopt a 21-day juice fast for different reasons. For many, it’s a tool for weight loss, since consuming only juice (and raw, light foods in later phases of the diet) cuts calories down significantly. For others, a 21-day juice fast is intended to “detox” the body of heavy metals and other harmful substances. Still others use a 21-day juice fast as part of a spiritual practice, seeking the mental clarity that may come from fasting.
What You Can Eat on the 21-Day Juice Fast Diet
The parameters of a 21-day juice fast are quite variable. It’s largely up to you to determine what you will eat at different phases of the diet. That said, many plans involve the following:
- A seven-day phase of consuming only freshly made fruit and vegetable juices and water: Homemade juices are recommended, since commercially made juices may contain added sugars or other ingredients. Some people dilute their juice with equal parts juice and filtered water. Others drink 8 ounces (oz) of juice followed by 8 oz of water.
- A second phase of “light” eating: This often involves three to seven days of eating low-calorie, plant-based foods like soups, salads, and smoothies. Phase two is intended to allow your body to readjust to solid foods after a week of a liquid diet.
- A third phase of “raw” eating in which about 75 percent of your intake comes from fresh, raw foods: The other 25 percent can come from cooked foods. Meat and poultry are usually discouraged, as are cooking methods like frying and breading.
During the juices-only phase of the fast, you can drink juices with the following ingredients: Apples, Berries, Bananas, Citrus fruits, Kiwi, Pomegranate, Pineapple, Lemon juice, Watermelon, Bell peppers, Cucumber, Celery, Fresh herbs, Leafy greens like kale, spinach, and chard, Cruciferous vegetables like broccoli, cauliflower, and Brussels sprouts, Carrots, Zucchini.
Foods to Avoid include: Meats, including chicken, pork, beef, and lamb, Dairy foods like cheese, milk, and yogurt, Beans and legumes, Grains like bread, pasta, rice, oats, and quinoa, Nuts and seeds, Added fats like cooking oils, salad dressings, and mayonnaise, Sugar-sweetened beverages, Alcohol.
Potential Benefits of the 21-Day Juice Fast Diet (and Why They May Not Last)
By consuming only juice for a week (and very light meals for two additional weeks), you’ll trim your calorie intake considerably. For this reason, weight loss is likely during a 21-day juice fast, according to Houston Methodist.
However, Danahy cautions that juice fasting isn’t a healthy or sustainable path to long-term weight loss. Fruit and vegetable juices have virtually no protein, and are very low in calories. While that can promote weight loss, it’s mainly because you’re losing water and muscle. When you resume your usual eating habits, you’re likely to regain weight lost during a short-term fast, according to the Mayo Clinic.
Danahy says that the claim that a three-week juice fast will “detox” your body also doesn’t hold water. There is no scientific evidence that a juice diet helps you detox.
As for the mental and spiritual clarity purported to come from fasting, more scientific evidence is needed. In a small study published in 2023, men who did a water-only fast for eight days experienced no changes to their mental well-being.
However, another - older - small study looked at 52 young women who fasted for 18 hours. The women reported a variety of emotional impacts, from elevated positive feelings of achievement, reward, pride, and control to increased irritability.
While neither of these fasts looked specifically at 21-day juice fasts, they suggest that each person will have a unique mental, emotional, and spiritual response to fasting.
Risks of the 21-Day Juice Fast
Going on a 21-day juice fast isn’t without risks. Keep these in mind when considering this fad diet.
- Nutrient Deficiencies: Though fruits and vegetables have lots of important nutrients, they’re notably lacking in protein, fat, and certain micronutrients like vitamin B12, according to Houston Methodist. Going without these nutrients for too long could lead to deficiencies.
- Elevated Blood Sugar: Fruit juice is very high in sugar, which can cause high blood sugar in someone with diabetes or prediabetes, according to Diabetes.co.uk.
- Undesirable Changes from Low Fiber: A study published in 2025 found that juice diets lacking in fiber caused harmful changes to oral and gut bacteria after just three days. Meanwhile, low fiber intake could slow down your digestion, causing constipation.
- Unsustainable Weight Loss: Rapid weight loss isn’t usually lasting weight loss, according to the Mayo Clinic. Though a juice fast might melt away pounds quickly, it’s not a long-term solution - and could lead to a cycle of yo-yo dieting.
- Lack of Scientific Evidence: Scientific evidence doesn’t support juicing’s claim to detoxify the body or individual organs.
- Social Isolation: The restrictive nature of a 21-day juice fast could mean three weeks of difficulty socializing over meals. During this time, you might lose out on the pleasure of enjoying food with others.
Juicing vs. Blending: What's the Difference?
When it comes to incorporating fruits and vegetables into your diet in liquid form, it's important to understand the difference between juicing and blending.
Juicing involves using a machine to extract the liquid from fresh fruits or vegetables. The liquid contains most of the vitamins, minerals, and plant chemicals found in the fruit. During juicing, the pulp and fiber are separated from the juice.
Blending, on the other hand, involves breaking down the whole fruit or vegetable into a drinkable format. This means that the fiber remains intact in the final product.
Incorporating Juices into a Balanced Diet
Juicing can play a role in a balanced diet. If you are looking for high-fiber foods, whole fruits and vegetables are among the highest. Juices can complement your diet, but they shouldn’t replace solid food.