Scientists Find Juice Cleanses May Harm Your Gut and Boost Inflammation in Just 3 Days

The small study involved 14 people who followed one of three diets for three days: an all-juice diet, a diet of juice and food, or a plant-based diet. Participants provided stool, saliva, and inner cheek samples before and after going on the diets, as well as 14 days after they finished the eating plans.

Researchers found that people on the juice diet had “abundances” of inflammatory bacteria, which they linked to the high sugar, low fiber nature of the juice diet. Bacteria linked with gut permeability (the ability of the intestine’s lining to control what passes through into the bloodstream), inflammation, and cognitive decline also increased in the juice diet group.

“These findings suggest that short-term juice consumption may negatively affect the microbiota,” the researchers wrote in the conclusion.

The nutritionists we spoke with say they’re not shocked by what the study found. “These findings add to the growing evidence that short-term dietary interventions can significantly impact the microbiome,” says Scott Keatley, R.D., co-owner of Keatley Medical Nutrition Therapy.

Marie Borum, M.D., M.P.H., director of the division of gastroenterology at George Washington University Medical Faculty Associates, points out that this is a small study, which makes it hard to draw huge conclusions. “Nevertheless, this study demonstrates that importance of understanding the nutrient content of juices and prioritizing fiber intake in the diet,” she says.

Why might a juice cleanse negatively impact the gut?

There are a few potential reasons for this. “When you eat fruits and vegetables, you get fiber—which is great,” says Jessica Cording, R.D., author of The Little Book of Game-Changers. “But when you juice those foods, you miss out on the fiber for the most part. What’s left is primarily sugar.”

A high-sugar, low-fiber diet is “not a beneficial thing for health, including gut health,” Cording says.

Juicing also removes insoluble fiber, which adds bulk to stool and helps keep digestion regular, Keatley points out. Insoluble fiber “is essential for feeding beneficial gut bacteria and maintaining gut integrity,” he explains.

“The absence of fiber can lead to an increased abundance of bacteria that thrive on simple sugars, such as Proteobacteria, which are associated with inflammation,” Keatley continues.

For the gut microbiome, it’s important to consider the types and amounts of bacteria that thrive under healthy conditions, says Stephani Johnson, D.C.N., R.D.N., professor in the Department of Clinical and Preventive Nutrition Sciences at Rutgers University. “Beneficial gut bacteria rely on prebiotics and fiber—compounds indigestible by the human digestive tract—as their primary food source. Juice-only diets eliminate these crucial components, depriving these bacteria of essential nutrients.”

All of that sugar from juices can also fuel microbial populations that aren’t as good for you, he says. “Your gut microbiota is the ultimate ‘survival of the fittest,’ and it really becomes a mirror of whatever you eat,” Keatley says.

Are juice cleanses healthy?

No, juicing is not considered healthy. “I’ve been begging people not to do juice cleanses for 12 years,” Cording says. She calls the promise of fast weight loss and helping your body to detox “alluring,” but says results from juice cleanses are not what they seem.

“People lose weight when they do a juice cleanse because they’re eating less and peeing a lot, and they may even have more bowel movements,” she says. “But the weight they lose is mostly water weight.”

Not only may juice cleanses interfere with your gut microbiome, which helps with digestion and contributes to your immune system, Cording says that these are “terrible for your blood sugar,” because they can cause spikes and crashes. If you regularly experience blood sugar spikes and crashes, you could be at risk for developing a condition known as insulin resistance, which is a precursor to developing type 2 diabetes, Cording says.

But bodily inflammation is also a big concern. “This has been linked to chronic conditions like cardiovascular disease, diabetes, and neurodegenerative disorders,” Keatley says. “While a three-day juice diet may not cause lasting harm in healthy individuals, repeated or prolonged juice fasting could have cumulative negative effects.”

Can I still drink juice?

Keatley warns against using juicing as a main dietary strategy—but drinking juice is still okay, just not as your sole source of nutrients. “For those who enjoy fresh juice, pairing it with fiber-rich foods like nuts, seeds, or whole grains can help slow glucose absorption and support gut health,” he says. “But just eating the fruits and vegetables—even if it’s less than when you juice—is the best option.”

If you want to have juice, Dr. Borum suggests pairing it with whole foods. This “can balance the intestinal microbiome,” she says.

Johnson says you don’t need to avoid juice entirely, pointing out that there’s a big difference between having the odd glass of juice and a juice cleanse, where these drinks are your primary or only source of nutrition. “In moderation, incorporating a serving of juice can be a healthful and enjoyable way to boost micronutrient and antioxidant intake,” Johnson says. “However, juice-only diets are nutritionally inadequate, lacking essential fiber, protein, and healthy fats.”

The bottom line

Cording stresses that actual fruits and vegetables are still better for you. “Instead of a juice cleanse, consider how you might incorporate more nutrient-dense produce into your day and pair it with good, quality protein sources and healthy fat. Drink plenty of water, too,” she says. “These are things that can enhance the body’s natural detoxification systems, a.k.a. your kidneys and liver.”