Why is it that men are supposed to eat 2500 calories every day, and women only 2000?

Question: Why is it that men are supposed to eat 2500 calories every day, and women only 2000?
- Keywords:
  calorie,
  difference,
  gender
Asked by maddiec to Christina, Jess on 28 Jun 2013.
- Jess Bean answered on 28 Jun 2013:
  
  In general men are usually taller and heavier then women, and naturally have more muscles. All of these factors mean that they need more calories to run their bodies than women.
- Christina Pagel answered on 28 Jun 2013:
  
  you can work out how many calories *you* need a day by measuring your basic metabolic rate (how efficiently your body uses food to make energy) and then adjusting that to take into account how much exercise you do – so i need about 2300 calories a day and a male olympic swimmer up to 12000! But children and teenagers need more calories than adults because they’re growing lots and also learning so much!

Question: Why is it that men are supposed to eat 2500 calories every day, and women only 2000?