From my research ( mainly what tv dieticians/doctors have to say on sugar), is that refined sugars are the most unhealthy types. Sugars from fruit are much better for you however when you mash them in a smoothie 2 things happen. The first thing is that you tend to use a lot more fruit and consume it much more quickly thus you are getting a lot more sugar in 1 go, and secondly something to do with the sugar coming outta the fruit and how your digestive systems absorbs it is much more unhealthy for you than if you were to eat the fruit as a solid.