Fruits and vegetables are a form of carbohydrates therefore when you digest it, they turn into sugar. Before you think smoothies are bad for you, you have to remember that the sugars in your smoothies from your fruits and vegetables are natural sources of sugar.
Specifically for the lemon kale blast, the sugars are coming from the honey, the banana and the coconut water. If you would like to reduce the amount of sugar in this recipe, try reducing the amount of honey added and always use unsweetened coconut water. Another alternative is to add 50% water and 50% coconut water to still give you the flavor without the extra sugars.