How Juice Cleanses Could Damage Your Gut and Oral Health: What You Need to Know

Think your juice cleanse is healthy? A new study from Northwestern University might change your mind. It found that a diet made only of fruit and vegetable juice, even for just three days, can hurt your gut and mouth bacteria. This can lead to inflammation and even affect your brain health.

The researchers looked at three groups of healthy adults. One group drank only juice, another group had juice but also ate whole foods, and the third group ate only whole plant foods. They took samples of saliva, cheek cells, and stool before, during, and after the diets to track changes in bacteria.

The group that drank juice alone had the biggest increase in bacteria linked to inflammation. In contrast, the group that ate whole foods showed better bacteria balance. The juice plus food group had some bacterial changes, but they were less severe than in the juice-only group. This suggests that juicing without fiber can upset the gut environment, which may lead to health issues down the road.

“Many see juicing as a healthy option, but this study brings a new perspective,” said Dr. Melinda Ring, the study’s senior author.

Juicing removes fiber, an important part of fruits and veggies. Fiber helps good bacteria grow, which produce anti-inflammatory substances. When you drink juice, sugar-loving bacteria can thrive. The high sugar content in juice only adds to this problem, causing an imbalance in gut bacteria. This imbalance might also affect metabolism, immunity, and mental well-being.

Interestingly, the oral microbiome—bacteria in your mouth—changed quickly when people switched to a juice-only diet. Researchers found that good bacteria decreased while harmful bacteria increased, showing how swiftly diet affects oral health.

“This shows how quickly what we eat impacts our health,” Dr. Ring noted. “Changes in the oral microbiome reflect dietary shifts almost immediately.”

The researchers stress the need for more studies on how juice and similar diets affect the microbiome, especially in kids who often drink juice instead of eating whole fruits. The sugar and carbs in juice are crucial in affecting bacteria in both the gut and mouth.

Dr. Ring recommends that if you enjoy juicing, try blending instead to keep the fiber. Mixing juices with whole foods can help balance your gut health and keep those beneficial bacteria thriving.

Source: Luisa, M., et al. (2025). Effects of Vegetable and Fruit Juicing on Gut and Oral Microbiome Composition. Nutrients. doi.org/10.3390/nu17030458.