Many people swear by their periodic juice cleanses saying they make them healthier, but a new study shows the opposite may actually be true. Researchers at Northwestern University found even just three days of a juice-only diet can negatively affect the gut and oral bacteria and trigger inflammation consistent with cognitive decline.
NU scientists worked with a group of study subjects and divided them into three groups. The first had only juice, which was a combination of fruits and vegetables. The second had juice with some whole foods and the third ate only whole plant-based foods.
Researchers gathered saliva samples, stool samples and took cheek swabs before during and after the study period. And those samples were analyzed using gene-sequencing techniques to check for changes in bacterial composition.
The juice-only group saw a significant increase in bacteria associated with inflammation and gut permeability. The juice plus group saw some negative changes, but they were much less severe than those who only had juice. And the whole-food group saw positive changes in bacterial composition.
That led researchers to conclude that consuming juice without the fiber normally associated with the fruits and vegetables can negatively impact the gut and mouth microbiome.
"Most people think of juicing as a healthy cleanse, but this study offers a reality check," said senior author Dr. Melinda Ring. "Consuming large amounts of juice with little fiber may lead to microbiome imbalances that could have negative consequences, such as inflammation and reduced gut health."
Juicing takes away the fiber associated with fruits and vegetables that feed the beneficial bacteria responsible for producing anti-inflammatory compounds like butyrate. That leaves sugar-loving bacteria free to multiply. The high sugar content in juice also contributes to the problem.
The oral bacteria showed the quickest and most dramatic changes with the juice-only diet. There was a reduction in Firmicutes bacteria and an increase in Proteobacteria, which is associated with inflammation.
"This highlights how quickly dietary choices can influence health-related bacterial populations," Ring said. "The oral microbiome appears to be a rapid barometer of dietary impact."
The scientists from Northwestern said the study shows the need for more research on how juice impacts the microbiome, especially in children who often have juice as a substitute for fruit.
"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," said researcher Maria Luisa Savo Sardaro.