What makes a smoothie unhealthy, and what you need to know to make the Sugar laden fruit juices: Most fruit juices sold in super markets are nothing more. And intuitively, it seems like this might be a great way to get healthy. You get all the stuff in the fruit or vegetable and you get it conveniently. That doesn't mean smoothies can't be good for you. You just Frozen fruit (with no added sugar) will make your smoothies thick and frosty.