We all have varying levels of taste when it comes to sweetness. For me personally, as I've incorporated less sugar into my diet over time, I've gotten used to things tasting less sweet. Bananas are great natural sweeteners and they are often more than enough when you're making a smoothie. If you don’t like bananas, applesauce is a great substitute or you can sweeten up your smoothie with dates, honey, real maple syrup (not cheap table syrup), stevia or molasses.