Almost everywhere you look it’s promoted that juicing can reduce your risk of cancer, boost your immune system, remove toxins from your body, aid digestion and help you lose weight. However, there's no scientific evidence that extracted juices are healthier than the juice you get by eating the fruit or vegetable itself.
our bodies need fiber from whole food to get the nutrients we need. Juices are an insulin trigger that cause sugars to be rapidly digested. Your insulin receptors eventually lose their sensitivity which is the beginning of developing diabetes. The truth is, our body does not need help detoxifying. Our liver produces the enzymes to break down toxins and the kidneys handle water soluble materials.
liquid cleansing and juicing deplete the body of needed proteins and calories. Depriving the body in this way will cause metabolism to slow and send you into starvation mode. This will cause the body to use fat cells and proteins for energy, instead of glucose that we should be getting from Whole Foods.

https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/juicing/faq-20058020

sources: https://www.livescience.com/48887-juice-cleanse-dangers.html