The researchers found that it didn't seem to matter how much food was served -- the teens still took in about half of their daily calorie needs in that one meal. The researchers suggested that certain factors inherent to fast food might promote overeating:
It's low in fiber.
It's high in palatability (that is, it tastes good).
It offers a high number of calories in a small volume.
It's high in fat.
It's high in sugar in liquid form.