Mar 04, 2025 07:00:00

Drinking only fruit and vegetable juices for just three days can be detrimental to your health

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Juice cleansing ,' which involves not eating solid food for a certain period of time and supplementing nutrients only with juice, has been attracting attention as it is expected to give the digestive system a rest, increase metabolism, restore internal organs, and improve immunity. However, new research has shown that replacing all meals with only vegetable and fruit juice may have a negative impact on health.

Effects of Vegetable and Fruit Juicing on Gut and Oral Microbiome Composition
https://www.mdpi.com/2072-6643/17/3/458

Juicing may harm your health in just three days, new study finds - Northwestern Now
https://news.northwestern.edu/stories/2025/02/juicing-may-harm-your-health-in-just-3-days-new-study-finds/

Just 3 Days of a 'Juice Fast' Could Be Doing You More Harm Than Good : ScienceAlert
https://www.sciencealert.com/just-3-days-of-a-juice-fast-could-be-doing-you-more-harm-than-good

In recent years, juice cleanses, which involve replacing meals with juice and avoiding solid foods, have been gaining attention among health and beauty conscious people. There are also people who don't like eating vegetables as part of their meals, so they make up for it by drinking vegetable and fruit juices.

However, since much of the insoluble dietary fiber is removed during the process of juicing vegetables and fruits, it is possible that the health benefits inherent to vegetables and fruits may be lost. Therefore, a research team from Northwestern University and the University of Illinois at Urbana-Champaign in the United States had subjects spend their time on a juice-only diet and investigated what changes would occur in their bodies.

The research team recruited 14 healthy volunteers aged 18 to 35 years and randomly assigned them to one of three groups: a group that consumed only cold-pressed juice made from vegetables and fruits, a group that consumed both cold-pressed juice and a regular diet, or a group that consumed only a plant-based diet.

The flow of the experiment is summarized in the diagram below. First, the subjects were assigned to three groups: 'Exclusive Juice', 'Juice plus Food', and 'Plant Base Food'. Before starting their diet, all subjects followed a diet centered on 'vegetables, fruits, gluten-free whole grains, and eggs' for three days. After that, they continued their assigned diet for three days, and then continued a diet centered on 'vegetables, fruits, gluten-free whole grains, and eggs' again for three days. The research team collected saliva and stool samples from the subjects at each time point and analyzed changes in the subjects' bacterial flora.

The results of the experiment showed that the group that only consumed juice had a significant increase in oral bacteria associated with inflammation and intestinal permeability. Although the changes in gut bacteria were not as significant as those in the oral bacteria, the proportion of bacteria associated with inflammation and cognitive decline was still higher after the three-day intervention.

The graph below shows the balance of oral bacteria in the following order from the left: 'group that consumed only a plant-based diet', 'group that consumed juice and meals', and 'group that consumed only juice'. The three graphs are 'pre-intervention', 'post-intervention', and 'post-intervention-14-days' from the left. Because the number of samples is small, the oral bacterial balance before the intervention is different, making it somewhat difficult to compare, but in the 'group that consumed only juice', it can be seen that the inflammation-related

Proteobacteria (pink) increased more after the intervention, and the beneficial ' Firmicutes (yellow-green) ' was greatly reduced. On the other hand, the change was small in the 'group that consumed only a plant-based diet', and the 'group that consumed juice and meals' was an intermediate change between the two. In addition, the bacterial balance returned to normal in all groups 14 days after the intervention.

The research team believes that the reason why a juice-only diet had a negative effect on the body's microbiome may be related to the loss of dietary fiber during the juicing process. Fiber serves as food for bacteria that produce anti-inflammatory compounds, and a lack of it can lead to the proliferation of bacteria that prefer sugar instead of fiber. The high sugar content of juice further encourages the proliferation of these harmful bacteria.

'The findings highlight how quickly dietary choices can affect health-related microbiomes,' said Dr. Melinda Ring of Northwestern University, co-author of the study. 'Consuming large amounts of low-fiber juice can lead to imbalances in the microbiome, which can have adverse effects such as inflammation and poor gut health.' For those who like juice, she recommended blending it in a blender to retain fiber or combining it with regular vegetables and fruits.