Juice cleanses: Are they doing more harm than good? Study results are very surprising

Juice cleanses have long been marketed as a quick way to detox and boost health. Many people believe that replacing solid food with fruit and vegetable juices can flush out toxins and improve digestion.

However, a new study from Northwestern University suggests otherwise. The researchers found that even a short-term juice-only diet can lead to changes in gut and oral bacteria.

These shifts are linked to inflammation and cognitive decline, raising concerns about the long-term impact of juicing. While juices provide vitamins and antioxidants, they also lack fiber, which plays a crucial role in gut health.

Impact of juicing

To understand how a juice cleanse affects the body, Northwestern scientists conducted a study on three groups of healthy adults.

The first group consumed only juice, the second combined juice with whole foods, and the third ate only whole plant-based foods.

Scientists collected saliva, cheek swabs, and stool samples before, during, and after the diets to analyze bacterial changes using gene-sequencing techniques.

The study aimed to determine whether a juice-only diet truly supports health or if it disrupts the delicate balance of bacteria in the gut and mouth.

Many people assume that juicing is a natural way to reset the body, but the findings suggest that it may do the opposite.

Juice cleanse and microbiome imbalance

The results showed that the juice-only group experienced the most significant increase in bacteria associated with inflammation and gut permeability.

The plant-based whole food group, on the other hand, saw more beneficial microbial changes. The group that combined juice with whole foods showed some bacterial shifts, but these were less severe than those seen in the juice-only group.

“Most people think of juicing as a healthy cleanse, but this study offers a reality check,” said Dr. Melinda Ring, director of the Osher Center for Integrative Health at Northwestern University Feinberg School of Medicine.

“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.”

Role of fiber in gut health

One of the biggest concerns with juice cleanses is the removal of fiber. When fruits and vegetables are juiced, most of their fiber content is stripped away.

Fiber feeds beneficial bacteria in the gut, helping them produce anti-inflammatory compounds like butyrate. Without fiber, sugar-loving bacteria multiply, and the high sugar content in juice fuels their growth.

This imbalance can lead to gut dysbiosis, a condition where harmful bacteria outnumber beneficial ones. Over time, this can increase the risk of digestive issues, weakened immunity, and even mental health problems.

The study also suggests that reduced fiber intake may negatively affect metabolism, making it harder for the body to regulate blood sugar and energy levels.

Oral microbiome changes rapidly

The study revealed that while gut bacteria remained relatively stable, the oral microbiome responded quickly to the juice-only diet. Scientists observed a decline in beneficial Firmicutes bacteria and an increase in Proteobacteria, a group associated with inflammation.

“This highlights how quickly dietary choices can influence health-related bacterial populations,” said Ring. “The oral microbiome appears to be a rapid barometer of dietary impact.”

The shift in oral bacteria suggests that juicing may contribute to inflammation in the mouth and throat, which could have implications for overall health. A disrupted oral microbiome has been linked to conditions such as gum disease, cavities, and even cardiovascular problems.

Need for further research

While this study highlights the potential risks of juice cleanses, more research is needed to understand how different diets impact the microbiome, especially in children.

Many parents substitute whole fruits with juice, believing it offers the same benefits. However, this study suggests that juice may not be a suitable replacement due to its effects on gut and oral bacteria.

“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 Maria Luisa Savo Sardaro, first author of the study and a professor of food microbiology at San Raffaele University in Rome.

Future studies may explore whether adding fiber back into juices or pairing them with whole foods can help mitigate these effects.

Understanding the long-term consequences of juice cleanses is essential for creating dietary guidelines that truly support health.

How to make a juice cleanse healthier

Despite the concerns raised by this study, people who enjoy juicing do not need to eliminate it completely. Instead, they can take steps to make it healthier.

One option is blending rather than juicing, as blending retains fiber while still delivering the vitamins and antioxidants found in fruits and vegetables.

For those who prefer juicing, pairing it with whole foods can help balance its effects. Eating fiber-rich foods alongside juice may prevent harmful bacterial shifts and support a more stable microbiome.

Choosing lower-sugar vegetables and incorporating ingredients like chia seeds or flaxseeds can also help maintain fiber intake.

“If you love juicing, consider blending instead to keep the fiber intact, or pair juices with whole foods to balance the impact on your microbiome,” noted Ring.

Rethinking juice cleanses

The idea of a juice cleanse may sound appealing, but this study challenges the assumption that juicing is always beneficial.

While juices provide essential nutrients, they also remove fiber, which is vital for gut and oral health. The findings suggest that consuming only juice, even for a short period, may cause microbial imbalances linked to inflammation and other health issues.

Rather than relying on juice cleanses for health benefits, individuals may see better results by focusing on a balanced diet that includes whole fruits and vegetables.

The study’s findings emphasize the importance of fiber and highlight how dietary choices can rapidly influence bacterial populations in the body.

Juicing may still have a place in a healthy diet, but it should not replace whole foods. By making small adjustments, such as blending or consuming juice alongside fiber-rich meals, people can enjoy the benefits of fruits and vegetables while maintaining a healthy microbiome.

The study is published in the journal Nutrients.

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