Juice fasting has many touted benefits that include reducing inflammation, improving sleep, clearing skin, promoting weight loss, ridding the body of toxins, and reducing sugar cravings. But are these juices really worth the hype? Most of these claims are unsubstantiated and anecdotal rather than science-based, but there may be some positives to note from short-term juice fasting.

Only one study to date has investigated the effects of a juice fast on health. This study looked at how a three-day fruit and vegetable juice fast affected the gut microbiota, weight loss, and body composition of 20 healthy people. During the fasting period, people drank six 16-ounce bottles of juices that were a mixture of leafy green vegetables, roots, citrus, cayenne, and vanilla almond, totaling around 1,310 calories per day. After the fast, people could then resume their normal diet for two weeks.

The results showed that people lost a significant amount of weight during the juice fast, and that weight loss persisted over the following two weeks (potentially due to changes in their gut microbiota). However, the weight loss may have resulted from lower calorie intake in general rather than from the juice specifically, and beneficial changes in people's gut microbiota may have been due to the overall increase of fruits and vegetables in the diet for those three days.

So basically, this study shows that a juice fast of this composition and calorie count for up to three days is safe and can be somewhat beneficial. But those benefits can't necessarily be fully attributed to the juice itself.