Many years ago, I wrote about the benefits of juicing. While it retains the nutrients of the produce, as time went on I realized that this may not be the best way to maximize what fruits and vegetables have to offer. That’s because juicing removes one key component from plant-based foods — dietary fiber, which is essential for optimal digestive health.
Study Reveals the Downsides to Juicing Fruits and Veggies
In a study published in Nutrients, researchers examined how juicing fruits and vegetables affect the composition of both gut and oral microbiomes, which are two important components for overall health. Specifically, they examined the consequences of removing fiber — which happens when juicing fruits and vegetables — and how this impacts microbial diversity and overall gut function.1
• Setting up the framework — Participants in the study included healthy adults with varying dietary habits, split into three groups. The first one consumed only juice, the second consumed juice plus whole foods and the third group only ate whole, plant-based foods. To analyze their oral and gut microbiomes, gene-sequencing methods were used on saliva, cheek swabs and stool samples before, during and after trials.2
• Creating a baseline — In addition, a three-day elimination diet was performed to create a baseline for all participants, which consisted of “organic fresh fruits, vegetables, gluten-free whole grains, eggs and eight glasses of water a day.” All of them were also instructed to avoid alcohol, caffeine, sugar, processed foods, dairy, red meat and glutenous foods.
• Results of the study — Based on the data collated, participants who consumed higher amounts of fiber saw an increase in beneficial microbes associated with gut lining protection and anti-inflammatory properties, while lower fiber intake led to a decrease in microbial diversity and an increase in bacteria linked to inflammation and metabolic dysfunction.3
What Happens When You Take Out Dietary Fiber?
In the juice-only group, researchers noted increased levels in the following bacterial strains in the gut — Porphyromonadaceae, Rikenellaceae, Coriobacteriaceae, Alcaligenaceae and Erysipelotrichaceae.
• Impact of inflammatory bacteria strains — These five strains are linked to pro-inflammatory effects that affect your health in different ways. “The Alcaligeneceae family has been positively correlated with cognitive impairment. The Porphyromonadaceae, Rikenellaceae and Coriobacteriaceae families have also been found to be overrepresented in stressed mice induced into a depression-like state.
Finally, Porphyromonadaceae and Odoribacteraceae have been correlated with anxiety-like behavior and increased gut permeability and inflammatory markers in aged mice,” the researchers said.4
• The elimination diet already provided benefits — Another notable discovery was how the elimination diet affected the Bacteroides and Firmicutes populations in the participants’ guts. Specifically, the researchers noted a slight increase in Bacteroides uniformis.5
• Improved athletic performance — In a different study, increasing the presence of Bacteroides uniformis led to an increased endurance in long-distance runners, as well as better fitness in test mice. While the study wasn’t able to trace the exact mechanism of how this occurs, the researchers theorized that the increased presence of Bacteroides uniformis works by mediating hepatic endogenous glucose production.6
The Lack of Fiber Affects SCFA Production and Gut Permeability
Beyond bacterial composition, the study also examined how the different diets they tested influenced SCFA (short-chain fatty acid) production. The researchers found that participants consuming more fiber had significantly higher SCFA levels (particularly the elimination diet), whereas those with lower fiber intake showed reduced SCFA production.7
• The role of SCFAs — SCFAs help regulate inflammation and maintain a healthy gut barrier. Without them, your gut becomes more susceptible to harmful bacteria and inflammatory responses.
• Importance of butyrate — The elimination diet increased Faecalibacterium prausnitzii, a strain that produces butyrate, which is an important SCFA that nourishes your gut in several ways. As noted by the researchers, “Butyrate is a main energy source for the colonocytes with protective properties against colorectal cancer (CRC) and immune-inflammatory chronic diseases like inflammatory bowel diseases (IBD) and Crohn’s disease.”8
• Lack of fiber negatively impacts gut integrity — Participants in the juice-only group had noticeable changes in their gut microbiome, specifically increased pathogenic bacteria. Moreover, “the gut microbiota also showed an increase in taxa associated with gut permeability, inflammation and cognitive decline.” What makes this worse is that these changes occurred in just three weeks.9
• Increased fiber intake benefits gut barrier integrity — Participants with a higher fiber intake had stronger gut barriers,10 reducing the risk of leaky gut syndrome,11 a condition where harmful substances pass through the intestinal wall into the bloodstream, triggering immune responses and systemic inflammation.12
According to the researchers, much of the barrier’s strength comes from the increase in probiotics that ferment dietary fiber, thus increasing the butyrate levels in the gut.13
Taken altogether, this study provides strong evidence that fiber is foundational for gut health, in large part by supporting beneficial bacteria and SCFA production. Removing fiber, as happens with juicing, disrupts these critical processes, creating an environment that favors inflammation and metabolic dysfunction.14
Is It Time to Reconsider Juicing?
Within the context of the study, it’s clear that dietary fiber is an important component to digestive health, and juicing instantly negates all the benefits. A lack of fiber in the diet has been linked to dysbiosis, an imbalance in gut bacteria that contributes to inflammation, metabolic disorders and weakened immune defenses.
• The verdict on juicing — According to their official press release by the authors, “Juicing strips away much of the fiber in whole fruits and vegetables, which feeds beneficial bacteria that produce anti-inflammatory compounds such as butyrate. Without fiber, sugar-loving bacteria can multiply.
The high sugar content in juice further fuels these harmful bacteria, disrupting the gut and oral microbiome. The study also suggests that reduced fiber intake may impact metabolism, immunity and even mental health.”15
• The role of fiber in gut health — Fiber acts as a prebiotic, meaning it feeds the probiotics (beneficial bacteria) living in your gut that ultimately contribute to improved digestive health.16
When you strip fiber away by juicing, you shift the microbiome’s balance, despite taking in the vitamins, minerals and bioactive compounds found in the juice. Other beneficial probiotics not mentioned in this study, such as Akkermansia muciniphila, also rely on fiber to maintain gut lining integrity, as well as producing butyrate.
The Impact of Juicing on the Oral Microbiome
Like your gut, your mouth also contains a mixture of microbes, both good and bad, and dietary factors such as lack of fiber affect this balance as well. Moreover, the oral microbiome experiences shifts faster than the gut microbiome since it immediately interacts with food, according to the Nutrients study.
• The importance of beneficial bacteria on oral health — The elimination diet, which consisted of whole, healthy foods, had a positive effect on the oral microbiome. “Despite the potential health risks observed with the elimination diet in the oral microbiota with increased Proteobacteria, an inflammatory microbe, Neisseria sp. and Haemophilus parainfluenzae were both also detected at higher levels.
These taxa are both commonly isolated from the mouth of healthy individuals and are not typically associated with oral disease, with Neisseria sp. also reported to have a possible physiological role in preventing colonization of potential pathogens,” the researchers said.17
• The science behind the downsides of juicing — The researchers theorize that the shift is due to the sudden increase of simple sugars, leading to an increase in pathogenic bacteria as well.18 Juiced veggies flood the mouth with sugars without the natural buffering effects of fiber. This environment promotes bacterial overgrowth, increasing the risk of cavities and gum disease. In contrast, whole foods require chewing that stimulates saliva production.
Strategies to Support Your Gut and Oral Microbiome
Based on the published research, juicing alters both oral and gut microbiomes, which have clear implications for your health. To support these two crucial systems, adding dietary fiber is essential. Removing it by juicing disrupts the delicate balance of beneficial bacteria, weakens gut barrier function and increases inflammation.
To counteract the lack of fiber, start with the most obvious step first — Prioritize eating whole fruits and vegetables over juicing. Whole fruits and vegetables give your body everything it needs — dietary fiber, polyphenols and structured water that hydrates without causing blood sugar spikes. Chewing also stimulates saliva production, which protects your oral microbiome from bacterial imbalances that lead to cavities and gum disease. Here’s are some other recommendations as well:
1. Blend your fruits and vegetables instead — Dr. Melinda Ring, co-author of the study, says blending is a viable alternative to juicing because it retains dietary fiber. But, if you still like to juice, Ring says that you’ll need to supplement it with whole foods “to balance the impact on your microbiome.”19
Also, if you juice fruits and veggies, don’t be too eager to finish your drink. Swallowing it too fast floods your system with sugar, overwhelming your microbiome and setting off inflammatory responses. Instead, sip juice slowly over time to avoid blood sugar spikes.
2. Increase fiber intake gradually to avoid digestive discomfort — Dietary fiber is an important component to nourishing beneficial gut bacteria and strengthening your gut lining. If you’ve been drinking juiced produce for a while, you’re likely low in fiber, so you’ll need to bump up your intake again, but don’t suddenly load up on it.
An imbalanced gut microbiome needs time to adjust. Start with easier-to-digest options like ripe bananas, cooked carrots and well-cooked white rice before moving on to raw vegetables. Slowly increasing fiber intake prevents bloating, gas and discomfort while allowing your gut bacteria to rebuild.
3. Make pulp-containing juices — Another way to enjoy juiced fruits and veggies without changing their essence is to add pulp. It contains fiber, and retaining some of it in your drink will help your gut microbiome. Again, pulp-free juice delivers a sugar surge without the buffering effects of fiber, which disrupts your gut and oral microbiomes.
4. Focus on microbiome-supporting foods — Support your gut microbiome with probiotic-rich foods that nourish the beneficial bacteria already living in your gut. I recommend sauerkraut, kimchi and grass fed raw dairy (if tolerated), such as kefir and yogurt.
Once your gut is able, add fiber sources, such as apples, sweet potatoes and squash to help nourish your gut microbiome. Also remember to avoid vegetable oils and ultraprocessed foods and drinks, as these damage your microbiome.
Frequently Asked Questions on the Impact of Juicing on Oral and Gut Health
Q: How does juicing affect gut health?
A: Juicing removes dietary fiber, which is essential for a healthy gut microbiome. A lack of fiber leads to an increase in pro-inflammatory bacteria associated with gut permeability, metabolic disorders and even cognitive decline. In contrast, consuming whole plant-based foods supports beneficial gut bacteria, increases short-chain fatty acid (SCFA) production and strengthens the gut barrier, thus reducing inflammation.
Q: What are the downsides of juicing compared to eating whole fruits and vegetables?
A: Without fiber, pathogenic bacteria multiply, leading to inflammation, metabolic dysfunction and gut microbiome imbalances. Additionally, juicing floods the system with sugars without the natural buffering effect of fiber, which leads to blood sugar spikes and increased harmful bacterial growth in the mouth and gut.
Q: How does juicing impact the oral microbiome?
A: Juiced fruits and vegetables introduce a high sugar load into the mouth without fiber, which fuels pathogenic bacteria. This increases the risk of cavities, gum disease and oral microbiome imbalances. In contrast, chewing whole foods stimulates saliva production, which helps maintain a healthy oral environment and prevents bacterial overgrowth.
Q: What are healthier alternatives to juicing?
A: Blending fruits and vegetables is a better option than juicing because it retains dietary fiber. Another alternative is making pulp-rich juices, which help slow sugar absorption and support gut health. If juicing is still preferred, it needs to be balanced with its whole food counterparts to maintain fiber intake and minimize negative effects on the microbiome.
Q: How can you improve your gut and oral health if you have been juicing frequently?
A: To restore gut and oral microbiome balance, gradually increase fiber intake with whole foods like bananas, cooked carrots and squash to avoid digestive discomfort. Incorporate probiotic-rich foods like sauerkraut, kimchi and kefir to nourish beneficial bacteria. Avoid vegetable oils and processed foods, which harm gut health.
