Yes and no. It's a special case. A third cup of corn kernels would be less than a full cob, which if eaten as corn, would be just a fairly empty calorie side dish and leave you still hungry.

As popcorn, it takes up much more volume in your stomach, and can give you a feeling of being full with far less calories and carbs than similar snacks such as potato or corn chips.

In short, it's one of the healthier snacks, but still need to watch for excessive fats from popping, if you didn't pop it yourself.