The fibre-free form of dieting favoured by celebrities including Beyonce and Coleen Rooney may increase inflammation-linked bacteria in the gut and mouth, new research suggests
Juice cleansing, a dieting trend popular among celebrities like Beyonce and Coleen Rooney, can have negative effects on your health in as little as three days, according to new research.
Scientists warn that this fibre-free diet may increase bacteria linked to inflammation in the gut and mouth. A US study, published in the journal Nutrients, found that a diet consisting only of vegetable and fruit juice for three days can cause changes in gut and oral bacteria associated with inflammation and cognitive decline.
Researchers at Northwestern University in Illinois studied three groups of healthy adults. One group consumed only juice, another juice with whole foods, and a third ate only whole plant-based foods.
The team collected samples before, during, and after the diets 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 and gut permeability, while the plant-based whole food group saw more favourable microbial changes.
The “juice plus food” group experienced some bacterial shifts, but they were less severe than the juice-only group. The researchers suggest that juicing without fibre may disrupt the microbiome, potentially leading to long-term health consequences.
Dr. Melinda Ring, the study’s senior author and director of the Osher Centre for Integrative Health at Northwestern University Feinberg School of Medicine, has warned that juicing may not be as healthy as people think. She said: “Most people think of juicing as a healthy cleanse, but this study offers a reality check.
“Consuming large amounts of juice with little fibre may lead to microbiome imbalances that could have negative consequences, such as inflammation and reduced gut health.” Dr Ring explained that juicing removes much of the fibre from fruits and vegetables, which is essential for feeding beneficial bacteria that produce anti-inflammatory compounds like butyrate.
Without fibre, sugar-loving bacteria can multiply, and the high sugar content in juice further fuels these harmful bacteria, disrupting the gut and oral microbiome. The research also suggests that a lack of fibre can affect metabolism, immunity, and even mental health.
The team found that while the gut microbiota remained relatively stable, the oral microbiome underwent “dramatic” changes during a juice-only diet. They discovered a decrease in beneficial Firmicutes bacteria and an increase in Proteobacteria, a bacterial group linked to inflammation.
Dr Ring added: “This highlights how quickly dietary choices can influence health-related bacterial populations. The oral microbiome appears to be a rapid barometer of dietary impact.”
The study’s lead author, Professor Maria Luisa Savo Sardaro from Northwestern University and San Raffaele University in Italy, has emphasised the significance of juice diets’ nutritional content, particularly their sugar and carbohydrate levels, on the microbiome. She stated: “The nutritional composition of juice diets – specifically their sugar and carbohydrate levels – plays a key role in shaping microbial dynamics in both the gut and oral cavity and should be carefully considered.”
Dr Ring further highlighted the importance of fibre in our diets, suggesting, “If you love juicing, consider blending instead to keep the fibre intact, or pair juices with whole foods to balance the impact on your microbiome.”
