Juice cleanses may cause changes to gut and mouth bacteria linked to cancer, a study warns.
Around a quarter of American adults are thought to have tried a juice cleanse, which sees people only consume juices from fruits and vegetables for a set amount of time.
They are popular for their claim to detox the body and drop weight, and have been used by Beyonce, Gwyneth Paltrow, and Gigi Hadid, the impacts on the gut and oral microbiome can raise the risk of developing certain cancers of the mouth and colon.
Researchers from Northwestern University found within three weeks, juice cleanses rapidly altered the body’s microbiome, the collection of healthy bacteria, and encouraged the growth of bacteria associated with inflammation and immune suppression.
When only consuming juices, people miss out on the fiber in whole foods, which promotes digestive health.
Additionally, subsisting on fruit and vegetable juices, which are often high in sugar, can cause rapid blood sugar spikes. They also lack protein and fat, which can lead to muscle loss and fatigue.
All the while, the body’s delicate balance of good and bad bacteria shifts toward the bad.
Dr Melinda Ring, lead study author and director of the Northwestern Medicine Osher Center for Integrative Health, said: ‘Most people think of juicing as a healthy cleanse, but this study offers a reality check.
‘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.’
For the study, published in the journal Nutrients, researchers experimented on 14 people with an average age of 22.7 years.
Participants were randomly assigned to one of three diet interventions for a three-day period: a juice fast (800-900 calories) consisting solely of cold-pressed juice; a combination of cold-pressed juice plus a regular diet; or a plant-based, whole-food diet (800-900 calories).
Researchers took stool, saliva, and cheek cell samples before diet changes, after completing the diet on day seven and two weeks after finishing the diet on day 21.
The biggest changes in the balance of good and bad bacteria were observed in the mouth, compared to the gut.
The researchers said: ‘The saliva microbiome was highly sensitive to diet variation, with rapid and significant changes in response to both the elimination and intervention diets.
‘In contrast… the gut microbiome changed very little in response to any of the diet treatments.’
When the balance of bacteria shifts toward the ‘bad’ kind, a series of negative effects can take shape.
Some bacteria can turn foods or substances into harmful compounds that damage DNA or encourage cancer growth. When the balance of bacteria is off, it can lead to the production of these dangerous compounds.
In the cheek microbiome, the juice-only diet increased Proteobacteria, a bacteria that has been linked to an increased risk of oral cancers.
An overgrowth of Proteobacteria can also cause chronic inflammation. This persistent inflammation can damage tissues over time, leading to genetic mutations that promote cancer development.
Over time, it also promotes abnormal cell growth, and weakens the immune system. This means cancer cells can persist and grow unchecked.
The juice-plus-food diet resulted in a decrease in Firmicutes bacteria, though less pronouncedly than juice-only, suggesting the hybrid diet may be a milder alternative.
Firmicutes play a significant role in digestion, particularly breaking down carbohydrates and producing proteins that are beneficial for gut health. Some strains are also instrumental in maintaining a healthy balance of the gut microbiome.
An imbalance in bacteria in the mouth and gut can compromise the gut lining, allowing harmful substances and bacteria to enter the bloodstream and trigger an immune response.
The microbiome plays a crucial role in maintaining the integrity of the intestinal barrier, though more studies are needed to better understand how an imbalance in the oral bacteria contributes to the development of cancer.
If you insist on juicing, however, Dr Ring said: ‘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.’
