New research from scientists at Northwester University looked at the impact of juice-only diets, and the results showed that they can be harmful in only a short period of time. When people consumed only fruit or vegetable juices for three days, there were changes in the oral and gut microbiomes, and these microbial communities can have a major influence on human health. Some of the shifts in those microbiomes were linked to cognitive decline and inflammation. The findings have been reported in the journal Nutrients.
In this study, the investigators assessed groups of healthy volunteers that had three different diets for three days: one group only consumed fruit juice; another group drank juice and ate a regular diet; the final group drank juice and ate a vegetarian diet. Cheek swabs and samples of saliva and stool were taken to analyze the microbiomes of the individuals before they started the diet, while consuming it, and after the diet was over. Metagenomics was used to identify the microbial species in the samples.
The most significant changes were seen in the oral microbiomes, while the gut microbiomes remained more stable on the different diets. When it came to the oral microbiome, people who only drank juice showed the highest increase in bacterial species that have been linked to inflammation. Individuals who ate a regular diet and drank juice had some of these deleterious changes, but to a lesser degree. Those who ate a vegetarian diet and drank juice had beneficial shifts in their microbiomes, however.
The study authors suggested that a juice-only diet may interfere with the microbiome because it lacks fiber. These changes in the microbiome may also have lasting, negative consequences. More research would be needed to confirm that hypothesis, however.
"Most people think of juicing as a healthy cleanse, but this study offers a reality check," noted senior author Dr. Melinda Ring, director of the Osher Center for Integrative Health at Northwestern University Feinberg School of Medicine and a Northwestern Medicine physician.
"Consuming large amounts of juice with little fiber may lead to microbiome imbalances that could have negative consequences, such as inflammation and reduced gut health."
Juice tends to lack fiber that is found in whole vegetables and fruits, and this fiber boosts the beneficial microbes in the oral and gut microbiome. These beneficial bacteria can help reduce inflammation, and lower the growth of harmful microbes. Good bacteria are also better for maintaining the health of the gut lining, which keeps microbes and the molecules they produce sequestered from the rest of the body. If that lining becomes permeable, some of those compounds may escape and lead to inflammation.
The growth of harmful microbes may also be fueled by the readily available sugars that are found in juice.
"This highlights how quickly dietary choices can influence health-related bacterial populations," said Ring. "The oral microbiome appears to be a rapid barometer of dietary impact."
'The study authors suggested that this work highlights the importance of fiber in a healthy diet.
Sources: Northwestern University, Nutrients