Juice cleanses have long been marketed as a quick and easy method for “detoxing” after periods of unhealthy eating or as a fast track to weight loss. Popular among wellness enthusiasts, these regimens often promise to flush toxins, boost energy, and reset the body.
However, a recent small-scale study offers a stark reality check about the potential health consequences of exclusive juicing diets, even those that last just a few days.
The findings suggest that these cleanses may disrupt the balance of beneficial bacteria in the mouth and gut, contributing to inflammation and potentially increasing the risk of long-term health complications.
Juice Cleanses May Trigger Harmful Microbial Changes
In a study led by researchers at Northwestern Medicine, a team set out to investigate how juice-only diets influence the delicate ecosystems of the human microbiome. Focusing on both the oral and gut microbiomes, the scientists discovered that a three-day juice cleanse could prompt significant and concerning bacterial shifts.
“Within just three days, we observed noticeable shifts in bacteria known to thrive on simple sugars and contribute to inflammation,” says the study’s senior author, Melinda Ring, MD, a physician at Northwestern Medicine and director of the Osher Center for Integrative Health at Northwestern University Feinberg School of Medicine in Chicago.
The study involved 23 participants, aged 18 to 35, with body mass indexes (BMI) ranging from 18.5 to 30. To maintain accuracy, anyone with a medical condition or on medications that could affect inflammation, blood sugar, or microbiome health was excluded. In the final microbiome analysis, 14 individuals—seven men and seven women—were studied in detail.
Participants were divided into three groups:
- One group consumed only cold-pressed juices.
- Another group followed a cold-pressed juice diet supplemented with whole foods.
- The third group ate a diet composed solely of whole plant-based foods, without juicing.
Saliva, cheek swabs, and stool samples were collected from each participant before the intervention, during the cleanse, and two weeks afterward. These samples were analyzed using advanced gene-sequencing techniques to evaluate changes in bacterial populations.
Significant Increases in Inflammation-Linked Bacteria
The group that consumed only cold-pressed juice experienced the most profound changes. There was a notable increase in bacteria associated with gut permeability—commonly referred to as “leaky gut”—and inflammatory responses.
According to the study, the shift was rapid and pronounced, raising concerns about the long-term or repeated use of juice cleanses.
“Most people think of juicing as a healthy cleanse, but this study offers a reality check,” Dr. Ring remarked.
Interestingly, the group that consumed whole plant-based foods without juicing exhibited favorable changes in their gut and oral microbiomes, underscoring the benefits of dietary fiber and whole food nutrition. The group that combined juice with whole foods showed intermediate results, with bacterial shifts that were less dramatic than the juice-only group but still notable.
The Oral Microbiome: The First Line of Defense
Perhaps most surprising was how quickly and dramatically the oral microbiome responded to the juicing intervention. The researchers found a reduction in beneficial Firmicutes bacteria and an increase in Proteobacteria, a group of bacteria associated with inflammation.
“The oral microbiome is the body’s first line of microbial exposure, playing a crucial role in the breakdown of food and interaction with the immune system,” Dr. Ring explains. “Changes in the oral microbiome can have cascading effects throughout the body.”
As harmful bacteria in the mouth proliferate, they can migrate to the gut, contributing to further imbalances and inflammation. This pathway may help explain why poor oral health is linked to systemic diseases such as heart disease, diabetes, and inflammatory bowel conditions.
“The connection between the oral and gut microbiomes suggests that maintaining oral health is integral to overall digestive and systemic health,” says Dr. Ring.
Is Short-Term Juicing Harmful?
Despite the concerning findings, nutrition experts like Jacquelin Danielle (J.D.) Fryer, RD, caution against overreacting. Fryer, a performance dietitian-nutritionist at Banner Sports Medicine High Performance Center in Scottsdale, Arizona, points out that a three-day juice cleanse isn’t likely to cause lasting harm for most people.
“In some situations, juicing could even be helpful,” Fryer says.
He explains, “For instance, a temporary fresh juice diet might be advantageous for stool impaction, autoimmune disorders, or skin conditions that require large boluses [single doses] of vitamins and minerals. Or someone who has just completed chemotherapy and lacks appetite and finds it challenging to eat enough of the nutrients that juicing can provide.”
However, Fryer stresses that the intervention in the Northwestern study was too brief to make any sweeping generalizations about long-term health impacts.
Why Fiber Is Crucial for Microbiome Health
The absence of fiber in a juice-only diet appears to be a key driver of the negative changes observed in the microbiome. Juicing strips away most of the fiber found in whole fruits and vegetables—fiber that is essential for feeding beneficial gut bacteria. These bacteria, in turn, produce anti-inflammatory compounds such as butyrate, which support gut health and help maintain the integrity of the intestinal lining.
Without sufficient fiber, sugar-loving bacteria can flourish. The naturally high sugar content in fruit juice may provide an ideal environment for the growth of harmful bacteria linked to inflammation and metabolic disorders. Moreover, fiber plays a vital role in slowing digestion and moderating the absorption of sugar into the bloodstream.
Proceed With Caution: Experts Advise a Balanced Approach
Given these findings, Dr. Ring advises people to be cautious about juice cleanses, especially if they are prolonged or performed frequently.
“While occasional juicing can supplement fruit and vegetable intake, the lack of fiber in a ‘juice-only’ cleanse can lead to imbalances in the microbiome and promote inflammation,” she says.
Instead of relying on juice cleanses to “detox,” Dr. Ring recommends a more sustainable and balanced approach.
“I advise patients to approach juice cleanses with caution, especially if they are prolonged or frequent,” she says.
“Instead of juice cleanses, I recommend whole-food diets rich in fiber, or if you enjoy juicing, consider blending rather than juicing to retain fiber. For those seeking ‘cleansing’ benefits, focusing on fiber-rich whole foods, hydration, and minimizing added sugars can be more effective and sustainable,” she adds.
Juicing for Weight Loss? Think Again.
For those turning to juicing in an effort to shed pounds, Alyssa Kwan, RD, of Stanford Health Care in California, offers a word of caution.
“The weight ‘lost’ is simply water weight that can easily be gained back,” she explains.
“I don’t usually recommend juicing, as it does not ‘detox’ the body; only the liver can do that,” says Kwan. “Not only does juice strip away fiber, it also lacks calories and protein important for muscle development.”
The Bottom Line: Moderation and Whole Foods Matter
While juicing may seem like an attractive option for a health reset or weight loss, the evidence suggests that its benefits are often overstated, and its risks are overlooked. Short-term juice cleanses may not cause lasting harm, but they can disrupt the balance of the microbiome in ways that contribute to inflammation.
The healthiest, most sustainable approach to supporting your body’s natural detoxification systems and maintaining a balanced microbiome is through a diet rich in whole, fiber-filled fruits and vegetables, adequate hydration, and limited added sugars.
However it’s important to remember before undertaking any extreme diet, it’s always wise to consult with a healthcare provider or registered dietitian.