Juicing does so many beneficial things for the body that it is hard to pin point the exact reason it is helping.
You're eating raw food with all the nutrition and enzymes intact. Antioxidants, vitamins, minerals, phyto nutrients, hormones, proteins and carbohydrates. This off the top of my head.
All in a concentrated form with no fiber to be removed.
Most of these diseases are caused by prolonged eating of cooked and processed foods. The body can no longer supply the enzymes to digest it. All the chemicals and preservatives also take their toll. Along with the GMO's and fake food. You will eventually get sick eating that garbage long enough, in large enough quantities.