whay is the daily recommended dietary allowance in USA (in serving)?

Answer 1

Because most people don't carry scales around.

Answer 2

The discretionary calories allowance is based on estimated calorie needs by age/sex group. Physical activity increases calorie needs, so those who are more physically active need more total calories and have a larger discretionary calorie allowance. The discretionary calorie allowance is part of total estimated calorie needs, not in addition to total calorie needs. The chart gives a general guide.

Age and sex Not physically active* Physically active**
Estimated
total
calorie
need Estimated
discretionary
calorie
allowance Estimated
total
calorie
need Estimated
discretionary
calorie
allowance

Children 2-3 years old 1000 calories 165*** 1000-1400 calories 165 to 170

Children 4-8 years old 1200-1400 calories 170*** 1400-1800 calories 170 to 195

Girls 9-13 years old 1600 calories 130 1600-2200 calories 130 to 290

Boys 9-13 years old 1800 calories 195 1800-2600 calories 195 to 410

Girls 14-18 years old 1800 calories 195 2000-2400 calories 265 to 360

Boys 14-18 years old 2200 calories 290 2400-3200 calories 360 to 650

Females 19-30 years old 2000 calories 265 2000-2400 calories 265 to 360

Males 19-30 years old 2400 calories 360 2600-3000 calories 410 to 510

Females 31-50 years old 1800 calories 195 2000-2200 calories 265 to 290

Males 31-50 years old 2200 calories 290 2400-3000 calories 360 to 510

Females 51+ years old 1600 calories 130 1800-2200 calories 195 to 290

Males 51+ years old 2000 calories 265 2200-2800 calories 290 to 425

Answer 3

For adults:
Dairy - 2-3 servings
Meats (or high-protein vegetable sources) 2-3 servings
Fruits - 5 servings
Vegetables 5 servings
Grains - 6-11 servings
Fats - 1

Food pyramid site has a chart by gender and age.