Key Highlights
- Short-term juice cleanses, typically lasting between three and seven days, are widely promoted for their supposed health benefits, such as detoxification, weight loss, and improved digestion.
- These cleanses involve consuming only fruit and vegetable juices, which are often homemade or purchased as costly commercial products.
- Despite widespread claims, scientific evidence supporting these health benefits is minimal, and a new study suggests they might have unintended negative consequences.
- Research indicates that even a brief three-day juice fast can disrupt the oral microbiome by increasing inflammatory bacteria while reducing beneficial bacteria, potentially leading to adverse health effects.
The Rise of Juice Cleanses: A Trend with Questionable Benefits
Juice cleanses have gained immense popularity in recent years, fueled by celebrity endorsements and social media influencers promoting them as a quick and effective way to detoxify the body, lose weight, and enhance digestion. These regimens typically involve consuming only fruit and vegetable juices for a designated period, often ranging from three to seven days. Proponents argue that by eliminating solid foods, the body can focus on flushing out toxins, resetting the digestive system, and promoting overall wellness.
Advocates of juice cleanses claim that they offer a variety of health benefits, such as:
- Purging harmful toxins from the body.
- Encouraging rapid weight loss.
- Positively altering gut bacteria to support metabolic health.
However, most of these claims remain anecdotal rather than scientifically proven. Health professionals, including those from the U.S. Food and Drug Administration (FDA), have expressed concerns about juice cleanses. They warn that such regimens might not supply sufficient energy and essential nutrients, leading to fatigue, nutrient deficiencies, and, in some cases, potential harm for individuals with pre-existing medical conditions like diabetes. Furthermore, the FDA has highlighted that some detox products are misleadingly marketed and may contain unregulated or harmful ingredients.
Now, a new study has provided further evidence that juice cleanses may not only be ineffective but could actually be detrimental to health. Even when using freshly made, natural fruit and vegetable juices, a juice-only diet for as little as three days can negatively impact the microbiome, particularly in the mouth.
Study Examining the Effects of Juice Cleanses on the Microbiome
A recent study, published in MDPI Nutrients, investigated the effects of juice cleanses on the oral and gut microbiomes. Researchers found that even a short-term juice cleanse altered the composition of bacteria in the mouth, increasing those associated with inflammation while decreasing beneficial bacteria. These findings suggest that juice cleanses may have unintended and potentially harmful effects on health.
Megan Mehnert, a UK-registered dietitian based in Bristol, emphasized the need to interpret these findings cautiously, stating: “It is difficult to draw meaningful conclusions from the study; as the researchers suggested, the sample size was small, intervention was short, and [the] population group is not representative of the wider population,” she told Medical News Today.
Despite these limitations, the study provides an important starting point for further research into the impact of juice-only diets on microbiome health.
Comparing Three Different Plant-Based Diets
The study aimed to assess how different dietary interventions influence the microbiome over a short period. Fourteen healthy participants, with a mean age of 22.7 years, were recruited for the 21-day study. To prepare their bodies for the intervention, participants first followed a three-day elimination diet. This diet consisted of organic fresh fruits, vegetables, gluten-free whole grains, and eggs while restricting caffeine, alcohol, sugar, processed foods, dairy, red meat, and gluten. Each participant was instructed to drink eight glasses of water daily.
After this preparatory phase, participants were divided into three groups, each following a different three-day dietary regimen:
- Group 1 (two males, three females) followed a juice-only diet, consuming 800-900 kcal per day from cold-pressed fruit and vegetable juices.
- Group 2 (two males, two females) maintained a regular diet but supplemented it with cold-pressed juices.
- Group 3 (three males, two females) adhered to a plant-based, whole-food diet with an intake of 800-900 kcal per day.
After the three-day intervention, participants followed a reintroduction diet for three days before resuming their usual eating habits. Researchers collected saliva, cheek swabs, and fecal samples at various points: before the study, after the elimination diet, at the end of the dietary intervention, and 14 days post-intervention. DNA analysis was conducted to identify changes in bacterial composition.
Increased Inflammatory Bacteria in the Oral Microbiome
The study found that the elimination diet had little effect on microbiome composition. However, after the three-day dietary intervention, those who followed the juice-only diet exhibited notable changes in their oral microbiome.
Analysis revealed an increase in Proteobacteria, a bacterial group linked to various inflammatory conditions, including gut disorders. At the same time, there was a decrease in Firmicutes, which play a crucial role in fermenting dietary fiber and supporting gut health. Similar but less pronounced changes were observed in the other two groups.
Interestingly, no significant changes were detected in the gut microbiome of participants in any of the groups. However, the researchers noted an increase in bacteria associated with inflammation in the juice-only group. Fortunately, most participants’ microbiomes showed signs of returning to their baseline composition within two weeks of resuming a normal diet.
Potential Health Risks Associated with Microbiome Changes
The researchers expressed concern that the changes observed in the juice-fasting group could have negative implications for overall health. They noted: “Many of the taxa that increased in relative abundance in response to the juice and juice-plus-food diets have been identified as potential critical risk factors for their involvement in increasing inflammatory markers, colorectal cancer, cardiovascular disease, gingivitis, and periodontal disease.”
Mehnert echoed these concerns, explaining that while juice cleanses may be rich in certain vitamins and minerals, they lack other essential nutrients necessary for optimal health: “Juice cleansing diets are often low in calories (and may not provide enough energy for our daily needs), and although they may be high in vitamins and minerals, they tend to lack a variety of other important nutrients that the body needs.”
Should You Try a Juice Cleanse?
Despite the widespread popularity of juice cleanses, experts caution against viewing them as a shortcut to better health. Mehnert specifically warned that they could be particularly harmful to individuals vulnerable to restrictive eating patterns.
“People with eating disorders may be vulnerable to restrictive diets, and a diet which doesn’t meet their energy needs, is low in protein, carbohydrates, fiber, fat, and dairy could further compromise their health and increase fear of food,” she stated.
Furthermore, she emphasized that detoxification is a natural process managed efficiently by the liver and kidneys, making extreme dietary interventions unnecessary. She added: “Generally, there is no quick fix to improve health, and for most of us, our liver and kidneys do a good job at detoxing the body. Fruit and vegetable juices can be part of a healthy balanced diet—UK Public Health England recommends that a small glass of fruit juice (150ml) a day counts toward your ‘5 a day,’ but no more, as juices are high in free sugar.”
Final Thoughts
While juice cleanses continue to be promoted as a way to detoxify and rejuvenate the body, this study suggests they may have unintended health consequences. The findings indicate that even short-term juice fasting can negatively impact the microbiome, increasing inflammatory bacteria and potentially raising the risk of various diseases.
Rather than adopting restrictive diets, experts recommend maintaining a balanced diet that includes a variety of whole foods. As Mehnert advised: “Aim to have balanced meals and snacks regularly throughout the day, with a focus on including a variety of different foods from all food groups. Any type of restrictive diet (including low-calorie diets) can make it difficult for us to get the right balance of nutrition to keep us healthy.”