We specified air-popped popcorn because the popcorn that you get from the movies or out of the microwave traditionally are coated in heavy, unhealthy oils and butter that add a lot of unnecessary fat. Popcorn is high in fiber since it is a whole grain, but it can too easily be high in calories when made with oil and butter.
Air-popped popcorn is super easy to make in an air popcorn maker. To make it, all you have to do is add the kernels into the machine, turn it on, and wait for the kernels to start popping! Add salt to finish it off, or get creative with different seasoning blends that add a lot of flavor for not a lot of calories!