Fiber is as close to the magic pill of weight loss as you're going to get. It's what fills you up to prevent hunger so you end up eating less later on in the day. Fruits do offer fiber but only if you pick the right ones. Bananas are one of the most common smoothie ingredients, but half of one only offers 1.4 grams of fiber. Aim to include at least 10 grams in your smoothie by adding fiber-rich foods such as berries, kale (it has twice as much as spinach), avocado, kiwi, pear, beans, flax meal, chia seeds, and certain plant-based protein powders.