As long as it's very temporary then ok, and as long as it's not for a huge loss of pounds fine. I would say that you need something in terms of protein and fat though. Yogurt or peanut butter in those smoothes will at least make your day tolerable. If I do juice fasts it would send me running to 5bowls of spaghetti in a day or 2.
Have you tried eating salads as a meal? I have found salads to be really enjoyable to make and can prep them a day ahead and take them with me when necessary. I put in a whole head of romaine, some cukes, green peas, avocado,carrots, radish, peppers, grilled chicken breast or tuna, or chickpeas. It takes a long time to eat, crunch crunch crunch, which makes you eat slowly and get full. And no matter what, by the end of the day you at least know that you've already got your daily 5!
"No matter how developed you are in any other area of your life, no matter what you say you believe, no matter how sophisticated or enlightened you think you are, how you eat tells all." - Geneen Roth