Popcorn contains about 31 calories per serving. Popcorn does not contain any vitamin A, C or calcium, but it has 1 percent of the recommended daily value of iron per serving.
There is 1 gram of protein and 1 gram of fiber in one serving of popcorn. Popcorn is a whole grain, which means it keeps people full for a longer period of time than a simple carbohydrate. Three cups of popcorn equal one daily serving from the grain group. A small amount of folate is found in popcorn as well as 1 percent of the recommended daily value of niacin.