A new Northwestern University study found that a juice-only diet can trigger shifts in gut and oral bacteria linked to inflammation and cognitive decline. The three-day diet was more detrimental to the microbiome than one with whole foods, highlighting the importance of fiber in maintaining balance.
Northwestern scientists studied three groups of healthy adults on different diets: juice only, juice with whole foods, and whole plant-based foods. They collected saliva, cheek swabs, and stool samples to analyze bacterial changes using gene-sequencing techniques. The results showed that the juice-only group had the most significant increase in bacteria associated with inflammation, while the plant-based whole food group saw more favorable microbial changes.
The juice plus food group had some bacterial shifts but less severe than the juice-only group. These findings suggest that juicing without fiber may disrupt the microbiome, potentially leading to long-term health consequences. The study’s senior author, Dr. Melinda Ring, notes that consuming large amounts of juice with little fiber can lead to microbiome imbalances, inflammation, and reduced gut health.
Fiber is crucial in maintaining a healthy microbiome, as it feeds beneficial bacteria that produce anti-inflammatory compounds. Without fiber, sugar-loving bacteria can multiply, disrupting the gut and oral microbiome. The study also suggests that reduced fiber intake may impact metabolism, immunity, and even mental health.
The oral microbiome responded quickly to the juice-only diet, showing a reduction in beneficial Firmicutes bacteria and an increase in Proteobacteria, a bacterial group associated with inflammation. The study highlights the need for more research on how juice and other diets impact the microbiome, especially in children.
To minimize potential harm, Dr. Ring recommends blending juices instead of consuming them straight or pairing them with whole foods to balance the impact on the microbiome.
Source: https://news.northwestern.edu/stories/2025/02/juicing-may-harm-your-health-in-just-3-days-new-study-finds