Eric Uthus. Popcorn is relatively high in fiber-a cup of air-popped popcorn contains just over a gram of fiber. It also contains 1 gram of protein and 6 grams of carbohydrate. It contains no cholesterol, it is virtually fat-free (only 0.1 g per cup) and contains only 100 to 150 calories in a serving of 5 popped cups.opcorn is relatively high in fiber-a cup of air-popped popcorn contains just over a gram of fiber. It also contains 1 gram of protein and 6 grams of carbohydrate.