New research found that a three-day “juice cleanse” wasn’t as beneficial for oral and gut microbiomes as eating a plant-based diet

New Research Shows How Juice Cleanses Could Actually Affect Your Gut and Mouth—And the News Isn't Great Here's why

• In a new study, participants who did a three-day “juice cleanse” had more pro-inflammatory bacteria in their oral and gut microbiomes than participants who ate a plant-based diet.
• Juicing removes most of the fiber from fruits and vegetables, which is essential for feeding beneficial bacteria in the body.
• Experts said drinking juice can be a convenient way to get in nutrients, but it isn’t a replacement for a balanced diet.

Juicing fruits and vegetables is a popular way to take in nutrients—but new research reveals that the juice, as they say, might not be worth the squeeze.

A study published in Nutrients in January found that people who went on a three-day “juice cleanse” had higher markers of inflammation in their oral and gut microbiomes than those who followed a plant-based diet. 

Even before this study’s release, many experts have cautioned that juicing’s reputation as a way to remove toxins or lose weight surpasses its actual health benefits.

Others add that juicing is fueled more by social influence than science. “I believe diet culture significantly drives the popularity of juicing in the U.S.,” Lisa Froechtenigt, RD, senior program management associate in the Baylor College of Medicine Bariatric Surgery Program, told Health in an email. “This culture is heavily influenced by celebrities, social media, and the behaviors of friends and family.”

Fruits and vegetables are, of course, an integral part of a healthy, balanced diet—but it might be better for your microbiome to eat them whole and leave the juicer behind. Here’s why.

Juicing’s Effect on the Microbiome 

The oral and gut microbiomes are involved in numerous aspects of health.

The colony of bacteria, fungi, and viruses in the mouth has been linked to Alzheimer’s disease, obesity, autoimmune conditions, and more. The gut microbiome, meanwhile, is a major area of research for its impact on mental health, cancer, diabetes, neurological disorders, and other conditions.

It's no surprise, then, that the Nutrients study isn’t the first to look at the effects of juicing on these two critical areas within the body. 

Previous research from 2018 examined the impact of adding a juice regimen to a normal diet. This combination resulted in improvements in fecal microbiota after three weeks.

Another study from 2022 found that people who followed a three-day juice fast had decreased diversity of gut microbes—but a second group that supplemented their juice fast with fiber appeared to have an increase in bacterial diversity.

The January 2025 Nutrients study built upon this previous research, using a slightly different design.

Fourteen adults ages 18 to 35 were divided into three groups: one that drank only a “cleanse” of juiced fruits and vegetables for three days, one that consumed the same juice for three days but could add whole foods as desired, and one that ate a diet of plant-based foods with the same calorie content as the juice-only group. 

As participants ate and drank their way through the three days, researchers kept close tabs on their oral and gut microbiota.

“We collected saliva, cheek swabs, and stool samples from participants before, during, and after they followed the three diets,” study author Maria Luisa Savo Sardaro, PhD, a research associate in the Department of Anthropology at Northwestern University, told Health. “DNA was then extracted from these samples, and a specific bacterial gene was sequenced to identify the bacteria present—similar to scanning a barcode to identify a product.”

The researchers then used statistical tools to determine how much the subjects’ bacterial populations changed after the diets.

“We found that the exclusive juice group had the most significant increase in bacteria linked to inflammation and gut issues,” Savo Sardaro said. “The juice-plus-food group also showed changes, but they were less severe.” 

Meanwhile, the plant-based whole food group showed favorable changes, such as an increase in bacteria that help with gut health and inflammation control.

Why Juicing Might Not Benefit the Microbiome

The process of squeezing liquid from fruits and veggies, casting off its pulp, leaves one critical nutrient on the table (or, rather, in the blender): fiber. 

According to Amy Moyer, RD, director of culinary medicine at the University of North Carolina, Greensboro, juicing can result in the loss of around 90% of fiber.

Meanwhile, as fiber gets extracted, sugar remains. “Decreasing fiber from the fruits and vegetables effectively increases the overall sugar and carbohydrate proportion of the resulting juice,” Moyer said.

The combination of low fiber and high sugar likely explains juice’s apparent unsavory effects on gut bacteria. “Fiber is essential for feeding beneficial bacteria that produce anti-inflammatory compounds like butyrate,” Savo Sardaro explained. “Without fiber, the bacteria that thrive on simple sugars—often linked to inflammation—can multiply.”   

What’s more, the juice-only group underwent the most drastic changes to their diet, which may inherently disrupt the balance of microbiota, Froechtenigt pointed out.

“The human body is not designed to consume only one type of nutrient or food. It requires a balance of macronutrients (proteins, fats, and carbohydrates—including fiber) daily,” she said. “When important food groups are removed from someone’s diet, the body may go into a type of ‘survival mode.’”

To Juice or Not To Juice?

If you’re looking for a wellness jump-start that increases your fruit and veggie intake, there may be better options than juicing. 

“Although the research is limited, I continue to recommend blending fruits and vegetables into a smoothie rather than juicing,” Moyer said. “This way, you aren't leaving valuable nutrition in the peels, skins, and seeds in the compost bin or garbage can.” 

Another possibility: Think of juice as an addition to your daily diet, not a replacement for foods as part of a “cleanse.”

Juicing can be a good way to stay hydrated and obtain some vitamins and minerals, but experts stressed that it's also important to incorporate plenty of fiber and other nutrients throughout the day. “Having juice with a meal is more ideal,” Froechtenigt said.

Edited by Health with a background in health, science, and investigative reporting. Previously, she wrote full time about parenting issues for the app Parent Lab. Before that, she worked as a reporter for National Geographic covering wildlife crime and exploitation." tabindex="0" data-inline-tooltip="true"> Jani Hall Jani Hall Jani Hall is a news editor for Health with a background in health, science, and investigative reporting. Previously, she wrote full time about parenting issues for the app Parent Lab. Before that, she worked as a reporter for National Geographic covering wildlife crime and exploitation. learn more

This story originally appeared on: Health News - Author:Sarah Garone