It is unheard of to get fat from drinking nutritional juice. Unless you are drinking sugar added extracts from your local food store, then NO, you will not get fat. As a bonus tip for a healthy body, drinking more vegetable juice is healthy than fruit juice.
Juicing is a great way to get your body all the nutrients it needs. Once your body is satisfied, it will demand less food, and you will have fewer cravings to feed. It is a proven way of losing weight and staying under a nutritionist diet.