When its blended its too easy to eat to much fruit. For an average sized smoothie most people would use a couple of bananas and a load of strawberries, so where you would usually only eat one banana at one time, now it is too easy to eat 2 or 3 times that amount in one sitting. Thats SW's theory on the matter. Though when you read about it, once fruit is blended or mashed it releases a lot of its natural sugars, so when you eat a piece it doesn't have time to excrete its sugars and its digested pretty fast, in a smoothie the sugars are released before you swallow it, making the calories higher. it's somethiing like that from what I remember, been a while since I looked into it.