The amount of food served at most restaurants has gotten bigger over time. While it may seem like "getting more for you money" is good, your mind can trick you into eating more than you realize -- and more than your body needs. A reasonable portion of fries is about the size of a baseball, or 10 fries. While people's calorie needs vary based on activity, gender and age, active male teens age 14-18 need as much as 3200 calories. A moderately active women needs about 2000 and a moderately active males would need 2,600. When you get 610 of those calories from fries, you've already eaten a significant portion of your calories for the day, leaving less room for more nutritious foods.