Combining bananas and blueberries with creamy, fat-free yogurt and a hint of agave nectar makes for a rich and satisfying smoothie that's also low in fat. Agave nectar comes from the agave plant–it's sweeter than honey and can be found in most grocery stores. This smoothie fuels you up with a healthy dose of potassium, vitamins C and B6, and plenty of antioxidants.