Many sources indicate that an average person requires about 2,000 calories per day. That number varies based on several factors, but is used as the target for this lesson. To prepare for the lesson, you might research some details on the Internet. For example, you can find out what various athletes consume in a day. You will find that it's much more than 2,000 calories. There was an urban legend floating around for a while that Michael Phelps (Olympic swimming gold medalist) was consuming 12,000 calories per day. That turned out to be untrue, but it might be interesting to start things off with a classroom discussion regarding how many calories various athletes consume. That could lead into a discussion regarding whether students know how many calories they consume and what proportion of nutrients are contained in the foods they eat.