Juice consumption can negatively affect the microbiota, especially the oral microbiota, by altering the bacterial balance and promoting the growth of microorganisms linked to inflammation. This suggests that, although juices can be a convenient way to increase nutrient intake, their excessive consumption, especially in exclusively liquid diets, can have negative impacts on health.
In recent decades, the number of people with chronic diseases such as diabetes, heart disease and certain types of cancer has increased worldwide. This growth is strongly linked to modern lifestyles, especially diet.
In industrialized countries, the typical diet tends to be high in sugar, fat and ultra-processed foods, but low in fiber and essential nutrients. This has led scientists to study in more depth how dietary habits influence the development of these diseases.
Scientific studies have shown that inadequate consumption of three essential dietary elements, whole grains, fruits and an adequate balance of sodium, may be responsible for more than half of diet-related deaths and two-thirds of the losses in quality of life caused by chronic diseases.
These findings were essential for the creation of global nutritional guidelines that encourage the consumption of a balanced diet, rich in natural and whole foods.
Among the most recommended foods are fruits and vegetables, which offer several health benefits. They have a low impact on blood sugar levels, promote greater satiety and help with weight maintenance.
In addition, they are sources of compounds called polyphenols, which can improve the body's sensitivity to insulin and influence the functioning of fat cells.
When consumed, these polyphenols are processed by the intestine and interact with the bacteria present there, bringing positive effects to immunity and reducing inflammation.
The fibers present in fruits and vegetables also play a fundamental role: in addition to aiding digestion, they serve as food for intestinal bacteria, promoting the production of substances that are beneficial for metabolism and immunity.
In view of these benefits, experts recommend that adults consume at least 1.5 to 2 cups of fruit and 2 to 3 cups of vegetables per day. However, many people find it difficult to reach this goal. Therefore, alternatives such as natural juices are gaining popularity.
In addition, practices known as “juice cleanses” or “juice fasts,” in which people consume only fruit and vegetable juices for a few days, have increasingly attracted followers, who seek benefits such as detoxification, weight loss, and improved digestion.
Recent reports show that around 26% of consumers have tried these diets, driving the growth of the juice market. Studies indicate that juices can provide important vitamins and antioxidants, such as beta-carotene, vitamin C, and vitamin E.
Some research also suggests that regular consumption of 100% natural juices can have positive effects on heart health, such as reducing blood pressure and improving cholesterol levels. However, the process of extracting the juice can eliminate essential fiber and change the way nutrients are absorbed by the body, impacting the balance of the intestinal microbiota, the set of beneficial bacteria present in the intestine.
Vitamin C is a substance that is sensitive to oxygen, light, and heat, so yes, it begins to degrade after the juice is extracted. At room temperature, orange juice can lose about 30% to 50% of its vitamin C in 12 to 24 hours.
B vitamins (such as B1 - thiamine) are also sensitive to oxygen, but they last a little longer than vitamin C. Vitamins A and E are more stable, since they are fat-soluble (dissolved in fat), and their degradation occurs more slowly.
Polyphenols and antioxidants can oxidize, but some remain active for several hours or even days.
While there are many studies on the effect of whole fruits and vegetables on the microbiota, few have analyzed how juice consumption directly affects these bacteria.
Another little-studied point is the impact of juices on the oral microbiota. Although most research on the microbiome focuses on the intestine, the oral cavity is the first to come into contact with the foods and beverages consumed.
There is a strong connection between the bacteria in the mouth and the intestine, and it is already known that alterations in the oral microbiota can be linked to inflammatory diseases, cardiovascular problems, insulin resistance and even neurological disorders, such as Alzheimer's. Some bacteria present in the mouth can also contribute to the development of autoimmune and metabolic diseases.
In periodontal disease, Porphyromonas species have been reported to induce the activation of the innate immune system, contributing to the development of rheumatoid arthritis, celiac disease, Alzheimer's disease, Crohn's disease and cardiometabolic disease.
To better understand how juice consumption affects both the gut and oral microbiota, researchers conducted a dietary intervention study. For three weeks, 14 participants followed one of three diets:
Only natural juices
A combination of juices and solid foods
A diet based exclusively on vegetables and whole foods
Researchers collected saliva, cheek swabs, and stool samples from participants before, during, and after the intervention. The samples were genetically analyzed to identify which bacteria were present and how their composition changed over the course of the study.
The results showed that the saliva microbiome underwent significant changes in the initial phase of the study, when the participants underwent a food elimination diet before the intervention.
The number of bacteria from the Firmicutes family, normally associated with a balanced microbiota, decreased, while the number of Proteobacteria, a group linked to inflammatory processes, increased.
After the consumption of the juice-based diets, there were further changes in the oral microbiota and in the mucosa of the cheek. Specifically, an increase in the presence of pro-inflammatory bacteria was observed, possibly due to the high intake of sugars and low intake of fiber, characteristics of the juices.
In the intestine, the researchers did not find significant changes in the general composition of the microbiota. However, an increase in bacteria associated with inflammatory processes and intestinal permeability was detected, a factor that may be linked to digestive problems, chronic inflammation and even cognitive decline.
Based on these findings, the scientists concluded that juice consumption may negatively affect the microbiota, especially the oral microbiota, by altering the bacterial balance and favoring the growth of microorganisms related to inflammation.
This suggests that, although juices may be a convenient way to increase nutrient intake, their excessive consumption, especially in exclusively liquid diets, may have negative impacts on health.
These results are important for refining nutritional recommendations and guiding healthier food choices. In addition, the study highlights the need for more research to better understand how different forms of food processing affect the interaction between diet, microbiota and human health.
READ MORE:
Effects of Vegetable and Fruit Juicing on Gut and Oral Microbiome Composition
Maria Luisa Savo Sardaro, Veronika Grote, Jennifer Baik, Marco Atallah, Katherine Ryan Amato and Melinda Ring
Nutrients, 2025, 17 (3), 458;
DOI: 10.3390/nu17030458
Abstract:
Background: In recent years, juicing has often been promoted as a convenient way to increase fruit and vegetable intake, with juice-only diets marketed for digestive cleansing and overall health improvement. However, juicing removes most insoluble fiber, which may diminish the health benefits of whole fruits and vegetables. Lower fiber intake can alter the microbiota, affecting metabolism, immunity, and mental health, though little is known about juicing’s specific effects on the microbiota. This study addresses this gap by exploring how juicing impacts gut and oral microbiome composition in an intervention study. Methods: Fourteen participants followed one of three diets—exclusive juice, juice plus food, or plant-based food—for three days. Microbiota samples (stool, saliva, and inner cheek swabs) were collected at baseline, after a pre-intervention elimination diet, immediately after juice intervention, and 14 days after intervention. Moreover, 16S rRNA gene amplicon sequencing was used to analyze microbiota taxonomic composition. Results: The saliva microbiome differed significantly in response to the elimination diet (unweighted UniFrac: F = 1.72, R = 0.06, p < 0.005; weighted UniFrac: F = 7.62, R = 0.23, p-value = 0.0025) with a significant reduction in Firmicutes (p = 0.004) and a significant increase in Proteobacteria (p = 0.005). The juice intervention diets were also associated with changes in the saliva and cheek microbiota, particularly in the relative abundances of pro-inflammatory bacterial families, potentially due to the high sugar and low fiber intake of the juice-related products. Although no significant shifts in overall gut microbiota composition were observed, with either the elimination diet or the juice intervention diets, bacterial taxa associated with gut permeability, inflammation, and cognitive decline increased in relative abundance. Conclusions: These findings suggest that short-term juice consumption may negatively affect the microbiota.
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