Cathy Sager, age 13, of McAllen, Tex., for her question:

HOW MANY CALORIES DOES A PERSON REALLY NEED EACH DAY?

Calories are units of energy supplied by food. The amount of calories a person needs each day depends on the person's sex, age, body build and degree of physical activity.

Children and young people up to 19 years of age need an average of 850 to 3,070 calories each day, depending on age, weight and sex. A husky, athletic girl or boy needs more calories than does a slight built, inactive student.

It is estimated that a moderately active man of average weight needs about 3,000 calories each day. A moderately active woman of average weight needs about 2,200.

Daily calorie intake by people in the poorest developing countries average under 2,000 calories, according to United Nations estimates. This is less than most people require. In many developed countries, daily calorie consumption averages over 3,200, more than most people really need.