Study changes 3-day fruit juice diet with unhealthy gut bacteria

According to a new Northwestern University study, the charm of juice cleaning is often more fictional than the facts. Studies show that three days of a fruit juice diet can significantly change bacteria in your intestines and mouth, potentially paving the way for inflammation and even affecting cognitive function.

The study, published in Nutrition, brings wrench into the popular concept of juice squeezing as a healthy detox. “Most people think juice is a healthy cleaning, but this study provides a realistic check,” Dr. Merida Lin, senior author of the study and director of the Osher Center for Integrated Health at Northwestern University Feinberg School of Medicine, Northwestern University (Melinda Ring) said. Medical doctor.

The study divided healthy adult participants into three groups: one consumed only juice, the other consumed juice with whole foods, and the third juice contained an entire plant-based diet. The researchers carefully collected saliva, cheek swabs and feces samples before, mid- and after dietary interventions, using advanced gene sequencing techniques to analyze bacterial changes.

The results are surprising. The bacteria in the pure juice group experienced the largest changes with increased inflammation and intestinal permeability. In contrast, the entire plant-based food group showed more favorable microbial changes. The juice plus food group is somewhere in between, showing some bacterial changes, although not as severe as the pure juice group.

So, what is the culprit? fiber. Juicing eliminates most of the fiber found in the entire fruit and vegetables. Fiber acts as a key food source for beneficial gut bacteria, which in turn produces anti-inflammatory compounds such as butyrate. Without fiber, bacteria that like sugar will multiply. These harmful bacteria often packed with sugar, which can additionally boost and destroy the delicate balance of the gut and oral microbiome. The study also suggests that this reduced fiber intake may have a broader impact on metabolism, immunity and even mental health.

Interestingly, the oral microbiome seems to be faster than the gut. A juice-only diet leads to a surge in bacteria and protein bacteria in the mouth, a group associated with inflammation. “This highlights how dietary choices affect the speed of the bacterial populations associated with health,” Ring explained. “The oral microbiome appears to be a fast barometer for dietary effects.”

The first author of the study, a research assistant at Northwestern University’s Amato Laboratory and a professor of food microbiology at the University of St. Raff, Rome, highlighted Maria Luisa Savo Sardaro, who emphasized the juice diet The importance of nutritional content. “The nutritional components of the juice diet (especially their sugar and carbohydrate levels) play a key role in making up the microbial dynamics in the gut and mouth and should be considered carefully,” Sardaro noted.

The research team stressed the need for further study on the effects of juice and other specialized diets on the microbiome, especially among children, who often use juice as a substitute for the whole fruit. They also pointed to the wider impact on dietary guidelines and food production, advocating priority to fiber.

For those who like juice, Ring recommends a simple tweak: “If you like juice, consider keeping the fiber intact or pairing the juice with whole foods to balance the impact on your microbiome.”

This study is not without limitations while raising important questions. The researchers acknowledged that the dietary intervention had a smaller sample size and a short duration, which may limit their ability to detect more subtle changes in the microbiome. They also noted that the study focused on healthy adults and the results may not be generalized to other populations. Future studies with larger and more diverse participants are needed to confirm these findings and explore the long-term health effects of juice squeezing.

Despite these limitations, the study can have valuable insights into the complex relationship between diet, microbiome, and health. This reminds people that even seemingly healthy diet options can have unexpected consequences, and a balanced diet rich in fiber remains the cornerstone of physical health.

The study, titled “The Effects of Plants and Juices on Intestinal and Oral Microbial Components,” was published online in the journal Nutrition on January 27, 2025. The study was funded by Northwestern University’s Oskhe Center for Integrated Health.