Juice-only diets may be harmful to health, according to new research.
Notably, juice-only diets increased the proportion of inflammation-causing bacteria in the mouth and gut.
The study, “Effects of Vegetable and Fruit Juicing on Gut and Oral Microbiome Composition”, was published in Nutrients.
Background
Juicing has gained popularity as a method for cleansing and detoxifying the body, prompting many people to start juice cleanse regimens for health benefits such as weight loss and improved energy levels.
Juicing can indeed be an effective way to increase the intake of fruits and vegetables, thereby boosting the consumption of essential vitamins like beta-carotene and vitamins C and E. Research also suggests that drinking fruit and vegetable juices may improve heart health by lowering blood pressure and enhancing lipid profiles.
However, unlike whole fruits and vegetables, juices are low in fibre. Fibre is crucial for promoting feelings of fullness, regulating blood glucose levels, and supporting gut health. The lack of fibre in juices could negatively impact gut health and overall well-being.
Oral health is an essential but often overlooked aspect of wellness. Studies indicate that oral health is linked to various health issues, including inflammation, heart disease, insulin resistance, and diabetes-related complications. Since the mouth is the first point of contact for the foods individuals consume, it is essential to consider how juicing might affect oral health.
Now, a team of scientists investigated how juice diets affect the oral and gut microbiome–the community of bacteria, fungi, and viruses that play a crucial role in health and disease.
How was the study done?
Fourteen individuals (seven males and seven females) with a mean age of 22.7 years participated in the study. For the first three days, they followed an elimination diet consisting of fresh fruits, vegetables, gluten-free whole grains, eggs, and water. During this period, participants were advised to avoid or eliminate alcohol, caffeine, sugar, processed foods, dairy, red meat, and gluten.
After the elimination period, they were randomly assigned to follow one of three diets for another three days: a juice-only diet, a combination of juice and regular food, and a plant-based, whole-food diet. After completing the dietary interventions, they engaged in a three-day reintroduction phase before returning to their usual diets.
The researchers collected various samples–stool, saliva, and check-swabs–at different time points: at the start of the study, after the elimination diet, immediately following the diet intervention, and finally, 14 days after participants resumed their usual diets.
What did the researchers find?
The oral microbiome was more sensitive to dietary changes than the gut microbiome. After the elimination diet, certain inflammatory bacteria in the mouth increased. However, alongside this, the number of beneficial bacteria that help eliminate harmful organisms increased, and bacteria associated with cognitive dysfunction decreased. Similarly, the elimination diet positively affected gut health by boosting the levels of bacteria that produce short-chain fatty acids, which are known to support both gut and immune health.
In contrast, juice diets raised the levels of bacteria linked to inflammation and various health concerns, such as colorectal cancer, cardiovascular disease, gingivitis, and periodontal disease, particularly in the mouth. Pro-inflammatory bacteria in the gut also increased after juice diets, although the changes were relatively minor.
“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,” Melinda Ring MD, senior author and director of the Osher Centre for Integrative Health at Northwestern University Feinberg School of Medicine said in a press release.
Interestingly, the oral and gut microbiomes generally returned to their typical composition 14 days after the juice diet. This suggests that a three-day juice fast may not be long enough to cause significant, long-lasting changes in the microbiome.
What are the implications of these findings?
Although juice-only diets are often marketed as a quick method for detoxification and weight loss, this research raises concerns about their potential drawbacks. These diets may increase in pro-inflammatory bacteria in the gut and mouth, likely due to their low fibre and high sugar and carbohydrate content.
“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, the first author and a research associate in the Amato Lab at Northwestern University, as well as a professor of food microbiology at San Raffaele University in Rome.
“If you enjoy juicing, consider blending to retain the fibre or pair juices with whole foods to balance their impact on your microbiome,” advised Ring.
It is essential to note that this study was short-term, lasting only about three days, so we cannot draw definitive conclusions about the long-term effects of juice diets. While juice diets may seem appealing, further research is necessary to fully understand their long-term impact on oral and gut microbiomes. Emphasising a balanced, whole-food diet may be more beneficial than a juice-only diet for maintaining adequate fibre intake and preserving gut and oral health.
The Take-home Message
Juicing can be a great way to boost your intake of essential vitamins and antioxidants. However, while it might lead to quick weight loss, its low fibre content may also pose risks to oral and gut health. Until more research is available, a whole-food diet is generally advisable. This means incorporating fresh fruits, vegetables, whole grains, nuts, seeds, and legumes to ensure sufficient fibre.
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