Juice fasting, a dietary approach that involves consuming only fruit and vegetable juices for a specified period, has garnered attention for its purported health benefits. Proponents suggest that it can clear toxins, aid in weight loss, and improve overall well-being. However, it's crucial to examine both the potential benefits and risks, with scientific evidence in mind.
What is Juice Fasting?
Juicing is a process that extracts juice from fruits and vegetables, often discarding the pulp and skin. Juice cleansing, a related practice, involves restricting one's diet to only fruit or vegetable juices for a period, typically ranging from three to ten days, while abstaining from solid foods.
Potential Benefits of Juice Fasting
While proponents of juice fasting tout various benefits, scientific evidence supporting these claims is limited. Some potential benefits include:
Increased Antioxidant Intake
Juicing may increase the bioavailability of vitamin C, flavonoids, and other beneficial phytochemicals. Studies have shown that consuming blended drinks leads to a higher availability of antioxidants and other active chemicals in plant foods compared to juicing the same fruits, such as apples, pears, mandarin oranges, and persimmons. These compounds may have antioxidant, immune-supporting, and antibacterial properties.
Weight Loss
Juice cleanses may lead to initial weight loss due to calorie restriction. A 2017 study found that participants on a 3-day juice-only diet experienced substantial weight losses. However, it's important to note that the participants consumed only 1,310 calories per day, which is below the recommended daily intake for weight maintenance. As such, being in a calorie deficit could lead to rapid weight loss.
Read also: 7-Day Juice Cleanse
Gut Bacteria Changes
Juice cleanses may help increase the number of healthy bacteria in your gut, which has been linked to weight loss. In a 2017 study, a 3-day juice-only diet altered the gut bacteria in 20 healthy adult participants.However, research shows that juice-only diets have a limited effect on gut bacteria composition.
Detoxification
Some detox treatments have been shown to improve liver detoxification and remove environmental pollutants from the body. An increase in fluid consumption can help kidney function, and some nutritional compounds may help in the removal of non-organic waste products in the body. However, the authors of a 2015 review suggest that these clinical studies have significant flaws in methodology and low participant numbers. Much of the promoted evidence also comes from animal research, which can’t necessarily be applied to humans.
Temporary Metabolic Changes
Juice fasting can cause some changes in body metabolism. Initially, the LDL level increases following the onset of fasting, but then decreases. There is a reduction in total cholesterol which lasts for about a week after fasting.
Risks and Downsides of Juice Fasting
Despite the potential benefits, juice fasting also carries several risks and downsides:
Limited Nutrient Availability
Juice fasting can lead to limited nutrient availability, as it may not provide enough proteins or fats, which are crucial for physical health, healing, and brain function. Eliminating food groups for extended periods may also lead to malnourishment. Juice cleanses are possibly unsafe, as they do not provide proper nutrition and can cause a person to develop nutritional deficiencies.
Read also: Explore the pros and cons of fruit juice detoxes.
High Sugar Intake
Pureed juice drinks contain a lot of sugar, in the form of glucose, and lack fiber. This can lead to many individuals feeling hungrier than usual, as their blood sugar levels spike and then drop. High blood sugar levels lead to stiffening of the red cell membrane, which hinders their passage through the body, increasing cholesterol deposits in the blood. Sugary foods and beverages like juice can cause pathogens that lead to cavities, but they can also trigger systemic inflammation throughout the body or affect the gut’s microbiome, says Tsang.
Loss of Muscle Mass
Juice fasting can lead to a loss of muscle mass due to the protein deficit. 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. Approximately two-thirds of the weight lost is lean mass, and one-third is fat mass. The excessive lean mass loss suggests that prolonged fasting may increase the breakdown of muscle proteins, which is a concern.
Unsustainable Weight Loss
Severe caloric restriction is not sustainable for most people and rarely leads to long-term weight loss. It may also increase a person’s risk of other complications. In most cases, a person will return to their starting weight quickly once caloric restriction ends.
Low Blood Sugar
Consuming an insufficient number of calories can cause a person to experience symptoms relating to low blood sugar, including fainting, weakness, dehydration, headaches, and hunger.
Dehydration
If a juice cleanse includes laxatives or other methods of bowel stimulation, a person could lose too many nutrients in their stool. This can lead to dehydration and imbalanced electrolytes.
Read also: Juice Cleanse: Benefits and Risks
Kidney Problems
Juice fasting has caused kidney problems in healthy people. People with existing kidney problems might be at increased risk for kidney injury from juice fasting. 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. 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.
Increased Risk of 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.
Negative Impact on Gut Microbiome
After a three-day, juice-only diet, participants in the 2025 study saw strains of bacteria associated with inflammation, gut lining issues, and cognitive decline increase in both their oral and gut microbiomes. "When you are juicing as opposed to having the whole fruits, you are eliminating most of the fiber,” says Dr. Rajapaksa. “And that is one of the really important nutrients that we get from fruits and vegetables that basically feeds and fosters the growth of a healthy microbiome.”
Not Suitable for Everyone
Juice fasting is possibly unsafe when pregnant or breast-feeding, as it does not provide adequate nutrition. Juice fasting does not provide balanced nutrition and might affect blood sugar levels and blood sugar control in people with diabetes. Anyone with kidney disease should not undergo a juice cleanse.
Prolonged Fasting: A Closer Look
Prolonged fasting, characterized by consciously eating little to no food or caloric beverages for several days to several weeks, has also gained attention for its potential metabolic health benefits. The main types of prolonged fasting are water-only fasting and Buchinger fasting.
Potential Benefits of Prolonged Fasting
- Weight Loss: Prolonged fasting for 5-20 days can produce mild to moderate weight loss of 2-10%.
- Blood Pressure Reduction: Systolic and diastolic blood pressure consistently decreased with prolonged fasting.
- Improved Glycemic Control: Reductions in fasting glucose, fasting insulin, insulin resistance, and glycated hemoglobin (HbA1c) were noted in adults with normoglycemia.
Risks and Downsides of Prolonged Fasting
- Lean Mass Loss: Approximately two-thirds of the weight lost during prolonged fasting is lean mass, which is a concern as it can lower resting metabolic rate and increase the risk of future weight regain.
- Variable Impact on Plasma Lipids: The impact of prolonged fasting on plasma lipids is less clear, with some trials demonstrating decreases in LDL cholesterol and triglycerides, while others show no benefit.
- Adverse Events: Metabolic acidosis, headaches, insomnia, and hunger have been observed in some studies.
Refeeding Effects
The metabolic benefits of prolonged fasting may not be sustained long-term. Studies have shown that 3-4 months after the fast was completed, all metabolic benefits were no longer observed, even when weight loss was maintained.
Alternatives to Juice Fasting
For those seeking to lose or maintain a healthy weight and support their body's natural processes, there are several 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. The recommended fiber intake varies based on age and sex, but a general rule of thumb is 25 to 30 grams of fiber per day, says Dr. Rajapaksa.
- 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.
- Smoothies: One delicious way to get the potential benefits of juicing, plus the natural fiber from these foods, is to enjoy fruits and veggies in smoothie form.